(Note: This Monograph has been reproduced by kind permission of the Commission for the New Towns now known as English Partnerships. It is published for general interest and research purposes only and may not be reproduced for other purposes except with the permission of English Partnerships who now hold the copyright of LDDC publications)

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Foreword

Docklands in 1981 presented a rare opportunity for engineers to display their full array of skills on a unique scale within a major urban conurbation. More than any other part of London, Docklands required the provision of extensive and major infrastructure on a massive scale - the expansion of basic utilities such as gas, water, electricity, the provision of drainage both surface and foul, as well as the construction of new roads and tunnels and rail and other transport networks.

Apart from new provision and investment, the condition of existing structures both on and below the ground had to be assessed including marine structures such as dock and river walls, lock gates and related infrastructure. All this as well as other elements had to be extensively surveyed before decisions could be made on what to renovate, repair or replace before the task of regeneration could commence.

In looking back it can be seen that London Docklands in 1981 was an untested market and much of the engineering design work had to be made in advance of known development requirements or private sector responses. Such circumstances posed a number of engineering challenges particularly in the early phases of the overall regeneration programme.

This monograph, one in a series published by the Corporation in its final year of operation, outlines how the Corporation's engineers together with their consultants contributed to the regeneration and physical transformation of London Docklands.

LDDC
March 1998

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Introduction

"At the beginning of 1981 London's Docklands bore the scars of 20 years of decline and neglect. Dock closures commencing in 1967 had led to the disappearance of related industries. New industry did not take the place of the old and 10,000 jobs were lost in the three years between 1978 and 1981. A shrinking and increasingly elderly population found itself isolated among wide tracks of derelict land and buildings.

"Conventional local government solutions failed to halt the accelerating decline. A new approach was needed. The London Docklands Development Corporation was created in July 1981 and charged with the regeneration of the area."

These words were written in 1986 by Nicholas Ridley, the then Secretary of State for the Environment in an article for "The New Civil Engineer" and they sum up exactly the situation which engineers and project managers found when work started in London Docklands in 1981.

As a result of the Corporation's initial investigations, a comprehensive programme of land acquisition, land reclamation, infrastructure provision, community support and marketing was put in place. This publication solely addresses the provision of infrastructure along with land reclamation programmes. Other issues are discussed elsewhere.

Part of the raison d'etre for establishing Urban Development Corporations (UDCS) and the London Docklands Development Corporation (LDDC) in particular was that the finance to support the infrastructure and land reclamation programmes on the required scale could only be funded by a Government agency using public money. it would have been impossible for any one developer or a consortia of developers to have funded the infrastructure and land reclamation programmes and justified economically the subsequent development.

Other programmes were also put in place, for it was seen as vital to provide not only the required infrastructure, but to enhance all aspects of the environment. The result of this was that certain buildings were listed and renovated. The fabric of churches e.g. the Nicholas Hawksmoor churches, St George in the East and St Anne's Limehouse, were restored and parks were created, together with community programmes.

The scene was therefore set. The Corporation would fund and provide the infrastructure and land reclamation and the private sector would provide and finance the developments.

The Corporation, early in its life, took the decision to employ in-house consultants to assist the chief officers and permanent staff in delivering its programmes. In the field of engineering and project management in 1981 there was initially only one permanent engineer.

The contract for managing the Corporation's Project Programme was awarded to W.A. Fairhurst & Partners, through competitive tender, who were employed in June 1982 and have retained the contract to March 1998. W.A. Fairhurst & Partners also provided many of the professional engineering staff. The in-house Quantity Surveyor consultants from 1982 to 1984 were Gardiner & Theobald. In 1984 following a competitive tender process McBains Cooper vvere appointed and likewise retained the contract until March 1998.

This structure was strengthened in 1990 when Bechtel International were appointed for a three year period to assist in the management, with W.A. Fairhurst & Partners, of major engineering projects under construction at the time, including the Limehouse Link Tunnel, the East India Dock Link Tunnel, the Lower Lea Crossing and work to Aspen Way, together with a major tunnel sewer project.

During its lifetime the Corporation has spent £2.3 billion on regeneration of which £1.86 billion was in Government grant and the remainder from property sales. Of this more than 50% was the responsibility of the Engineering and Project Management teams.

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Provision of Services

Of all the tasks facing the Corporation at the outset in July 1981, the provision of services was one of the most difficult. What level of development would they have to support? No one knew, indeed the whole venture was speculative. A development corporation on the scale of London Docklands had not been tried anywhere in the world and therefore had no precedent to give a guide.

Further, it was clear that the provision of services and other infrastructure would have to take place concurrently with development, this was especially true in Wapping and the Isle of Dogs, the latter of which housed the Enterprise Zone, for ten years from 26th April 1982. To have provided the infrastructure first in these areas would have taken several years and the whole momentum, which was vital if this venture was to prove a success, would have been lost. Simply the problem was, what would be required? What capacity of services would be required and what were the logistics of providing them 'cheek by jowl' with development.

However, in spite of there being no precedent, development frameworks were produced by the Corporation's planners in which assumptions were made about the type and density of development. Based upon these assumptions the services i.e. drainage, water supply, power and communications were sized. In the case of the Royal Docks and Southwark the capacity of these planned services were sufficient for the subsequent and planned development.

In 1984 it was thought that up to 8 million sq.ft (743,000 sq.m.) would be accommodated on the Isle of Dogs, attracted by the financial incentives and relaxed planning regime of the Enterprise Zone. However, by 1986 the LDDC had agreed in principle the proposed Canary Wharf development of some 12 million sq.ft. (1.1 million sq.m.). A complete rethink regarding the capacity of the services was required. By this time five years from the start of the LDDC some of these services had already been installed.

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Services in the Isle of Dogs - 

Drainage

By the 1850's the lack of a proper drainage system for London posed a serious health problem and diseases such as cholera had become endemic. In the Summer of 1857 Parliament rose early, due to the stench emanating from the river Thames and in 1858 the engineer, Joseph Bazalgette, later to become Sir Joseph Bazalgette, was commissioned by Parliament to design an effective drainage system for the whole of London.

Bazalgette's plan was to intercept the existing sewers, which at that time discharged directly to the Thames, prior to their entry into the river. These new sewers would drain by gravity to pumping stations, which in turn would pump them up to a high level sewer known as the Northern Outfall Sewer, which itself drained by gravity to Beckton. The site at Beckton was chosen because foul drainage discharged at that point would not be carried on the tide up as far as London. Since that time Beckton has become the home of a major treatment works and now only clean water is discharged into the Thames. The system designed by Bazalgette was based upon a combined system with both foul and surface water discharging into common sewers. In times of storm this system has the distinct disadvantage that if flooding ensued then an element of the flood water would be made of foul sewage. However, to prevent flooding as far as possible, the system has an in-built safeguard which either allowed for the overflow to discharge via weirs to the Thames or a pumped overflow to the River, neither of which is an ideal solution.

Figure 1 shows the strategic drainage system which had in the main been in existence since the 1860s.

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In the early 1980s the Corporation commissioned a study of the capacity of the existing system, set against the development predictions at that time. This was prior to the advent of Canary Wharf.

Due to the development predictions for the Isle of Dogs it became clear that the capacity of the existing system would be exceeded by both foul and surface water discharges - the foul, due principally to the increase in residential development, and the surface water, due to the construction of highways and hard standing such as car parking areas and so on.

Following this study two options emerged, the first and the one which was eventually constructed was to enhance the drainage to the Isle of Dogs and take it north to Abbey Mills, via the new Northern Drainage Scheme Phase 2, as shown on Figure 2. From Abbey Mills it would be pumped into the Northern Outfall sewer and thus discharged at the Beckton Treatment Station.

The second, and more imaginative scheme, was once more to enhance the drainage of the Isle of Dogs, but to pump across the River Lea and discharge it into the then planned drainage at the south west corner of the Royal Victoria Dock. It would have then been routed to the planned North Woolwich (Store Road) Pumping Station from where it would be pumped to Beckton. However, due to the development forecasts at that time it was not considered economic. However, with the coming of Canary Wharf, it quickly became obvious that this scheme would have had distinct advantages. By the time Northern Drainage Phase 2 was constructed in 1990, it was too late to pursue the second option, since the Royal Docks station which had been installed did not have the capacity to take this extra flow.

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The strategy for the first option was to incorporate the enhanced drainage system into the existing system and where possible separate the foul and surface water discharges. The discharge of as much surface water as is possible to the Thames is important in terms of energy saving in that it obviates the need to drain it from the Isle of Dogs to Beckton, a distance of some 5 miles (10 km), and then treat it. To implement the building of this system required the construction of two Pumping Stations, one at Stewart Street on the Isle of Dogs and the other at Abbey Mills.

The Stewart Street Pumping Station designed by Sir William Halcrow & Partners, with John Outram architects, was built by Peter Birse Ltd while the Abbey Mills pumping station was designed by Halcrow and built by Miller Civil Engineering. Halcrow were the principal consultants for Northern Drainage while the main contractors were Millers and Lilley Construction.

The Stewart Street pumping station pumps the surface water from the eastern trunk sewer in Marsh Wall and, in times of storm, it pumps the excess combined flows to the river. In normal circumstances all flows are collected in a "mega manhole" in the centre of Prestons Road Roundabout from where they flow northwards to Abbey Mills, either in the old low level No. 1 Isle of Dogs branch sewer built in 1860, or the new Isle of Dogs low level No.1 sewer constructed in 1993.

To choose a route for this new major sewer presented a difficult task. For safety reasons the building of the sewer required the construction of 15 shafts, the positions of which in the main predetermined the route of the sewer. The construction of many of the shafts resulted in the diversion of services, changes to traffic flows and some inconvenience to the local community. However, with careful planning, the co-operation of the Police, and the local residents, the disruption was kept to a minimum. The route itself commences adjacent to the manhole in Prestons Road, from there it goes north crossing under the A102 north of the southern entrance to Blackwall Tunnel, from there it proceeds northwards under Gillander Street to the main construction shaft at Twelvetrees Crescent. From Twelvetrees Crescent it proceeds northwards crossing under a main water course and ring at Abbey Mills. The construction of the sewer took place at a lower level than the existing low level No.1 sewer to take advantage of the presence of London Clay, a material ideally suited to tunnelling.

Northern Drainage Phase II was a major infrastructure project and the first addition to the existing foul drainage of London built since the 1860s.

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The construction of the tunnel employed the use of two different types of tunnel lining, the section south of Twelvetrees Crescent consisted of an expanding one pass lining, that is the rings are held in place by the presence of a horizontal keystone, the placing of which expands the other segments of the ring against the London Clay. The second type of lining i.e. that north of Twelvetrees Crescent was constructed at the interface of the London Clay and the Woolwich and Reading Beds, a water bearing strata. This section of the tunnel was constructed under an air pressure of 1 bar and employed the use of bolted segments which were later relined.

Electricity

As with drainage the level of electric supply to the island was insufficient for the forthcoming development. The first upgrading to the existing system took place in 1984 and as a result a new 1 1 KV transformer station was constructed at Simpsons Road in Poplar. This substation took its 132 KV feed from the nearby Brunswick Power Station and the construction of Aspen Way gave the opportunity to lay the feed cable with the road construction, thus minimising disruption to the area. The second phase of upgrading took place as a result of the Canary Wharf development. The agreement between Olympia & York and the Corporation required the Corporation to supply electrical power at 11 KV, and resulted in the construction of an 11 KV substation at Ontario Way. This substation took its 132 KV feed from the West Ham power station.

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Gas

The gas distribution in 1981 for the Isle of Dogs was based upon a low pressure system. With the predicted flows it was impossible to satisfy the demand using a low pressure system. Since the existing pipes could not sustain an upgrading to medium pressure these pipes had to be replaced. Once more to minimise disruption, the installation of new pipes was, where possible, undertaken together with works to the highways.

The main supply to the Isle of Dogs was taken from two 48" mains located in the A13 trunk road, but with the new demand it was necessary to tap into the high pressure system on the east side of the River Lea and to bring a feed across the river via a pressure reduction station.

Telecommunications

The major provider of telecommunications was, and is, British Telecom, however following privatisation other companies entered the market including East London Telecommunications, Mercury and City of London Telecommunications.

During the road building programme, the opportunity was taken to lay banks of ducts, generally in the footpath. Each of the companies were allocated dedicated banks of ducts and the opportunity was also taken at this time to lay ducts for general traffic signalling throughout the area. In deciding the number of layout of the ducts close co-operation was undertaken with the various companies to satisfy their demand.

Ron Berry C.Eng., M.I. Struct. E.
LDDC Head of Engineering
(formerly W.A. Fairhurst & Partners)

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Strategic Sewerage and Services in the Royal Docks

The Royal Docks are situated in the eastern part of the LDDC's area and comprise the predominantly residential area of Beckton in the north, and the former Port of London area - the docks - in the south. The Royal Docks system formed by the Royal Victoria, Royal Albert and King George V Docks is impressive, both in scale and its visual impact, but despite these attributes, provided the greater challenge to sewerage and servicing provision. These principal development areas are illustrated on Figure 1 (151k) , together with the details of the sewerage and services discussed in this section.

Development of the Beckton area commenced early on in the life of the Corporation, carrying on work already started by the London Borough of Newham. Development has been carried out on land formerly used by Beckton Gasworks, along with allotments and existing waste ground. Servicing of development sites by new sewerage and the other services has been successfully achieved by the new provision and reinforcement of existing services within, and at the boundaries of, the area. Sewerage and services construction has followed a conventional approach with appropriate measures taken in recognition of areas of contamination, consequential on previous land use. Beckton (as at 1998) has capacity for further development, and any additional services provision for the few remaining sites will be generally met by connection to the existing network of sewers and utilities.

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Services in the Royals

The LDDC's acquisition from the Port of London Authority in the mid 1980s of the Royal Docks presented a challenge to sewerage and services provision, principally due to the relative positions of the dock water and adjacent land area. The principal feature of the docks system, which subsequently dictated the configuration of the eventual sewerage and services layout, is the vast impounded area of dock water amounting to some 100 ha., surrounded by the quay side development area of 140 ha.

The linear shape of the docks, which have a total length of 4.5 km from the western to the eastern extremities with a depth of dock water up to 9 metres, formed the main constraint which influenced sewerage and services designs. The water areas bisect the development land into the north and south side areas. The width of the dock waters varies from 180 metres, to a much narrower width where the Royal Victoria Dock and Royal Albert Dock meet at the Connaught Cut channel linking the two docks. The Royal Albert Dock and King George V Dock to the east of the Connaught Cut are separated by the London City Airport runway.

Alignments and the locations of the future sewerage and services runs were also significantly influenced by the linear shape of the development areas they were to service and by the barriers created by the dock water.

The level of provision of sewerage and services was determined initially with reference to the Corporation's Royal Docks development framework, prepared in 1985, by the LDDC with the Richard Rogers Partnership.

The LDDC has laid foundations for the successful future development of the Royals. Most of the infrastructure schemes have been completed, a number of high profile developments have been agreed and work on some of these schemes has started.

The development strategy proposed a variety of uses including commercial, residential, office, retail and leisure facilities. In 1986 with more detailed information available, and with the emergence of major development schemes in the Royals, the fundamental requirements to enable design of sewerage and services were established. The volume and scope of the proposed new development was much different than the existing land use, as an area for handling cargoes and an enclosed dock system. Quay side buildings, in this former use, included large warehouses and shipping offices, grain silos and flour mills, together with railway yards. The requirements and demand for sewerage and servicing needed to reflect the different conditions which would prevail after redevelopment. The docks, during their operational period, had been continuously redeveloped and, as a consequence, the underground sewerage and services had been sequentially adapted and modified to suit the changes. The process envisaged by the Corporation was therefore not new, but would require fundamental review of the existing sewerage and services infrastructure.

The run down of the docks during the 1970s and cessation of shipping activity resulted in the Royal Docks area becoming derelict. The combination of age and neglect of the buildings equally applied to the sewerage and services which, as a consequence, could not give the flexibility, the scope and the capacity to meet the requirements of the regeneration proposals envisaged by the Corporation.

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Sewerage and Drainage Network

The increase in services required for the proposed development could not be accommodated by existing sewerage infrastructure feeding out of the proposed new development area or services feeding into the area. The existing infrastructure had not been designed to meet the increased demands created by the planned increased volume of development. Much of the existing sewerage outside the Royals, which could potentially drain the new development and which was operated by the water authority, Thames Water, did not have the capacity to provide for the existing development and would need to be improved, irrespective of the redevelopment proposals. The existing sewerage network and sewerage proposals were examined in detail in conjunction with Thames Water prior to committing to design and construction. A similar exercise was undertaken for services with the other public utility authorities i.e. gas, electricity and so on. As with the existing sewerage and drainage within the docks system, the services infrastructure was formerly owned and operated by the PLA as a private network and in general would not meet the specification and standards of construction required by the statutory water and public utility authorities.

Redevelopment on the scale envisaged, to a programme determined to a great extent by market forces, would see a piecemeal provision of sewerage and services infrastructure over time by individual developers, unless a co-ordinated approach was adopted. The decision was taken by the Corporation to provide main sewerage and services in a co-ordinated manner as advance construction and as a means of enabling and encouraging development in a pump priming exercise. The costs to developers of procuring infrastructure in a piece-meal and less economic approach was thus obviated and development sites would be able more or less to 'plug-in' to a 'ring-main' arrangement. The 'ring-main' comprising the sewerage and services passes through a substantial portion of the Royal Docks to enable the principal sites to be serviced.

The fundamental requirements, which dictated the form of the new sewerage, were determined by the decision not to allow discharge of surface water run-off into the dock water, as had been allowed by the PLA and by the increase in foul sewage discharges as a consequence of the enlarged development. The separation of surface water and foul sewage discharges by means of separate foul and surface water sewerage systems, would enable less sewage to be pumped to and treated at the main Thames Water sewage treatment works at Beckton and would therefore reduce costs and place less burden on treatment capacity.

Surface water would be dealt with by discharge to the River Thames, thus maintaining the quality of water in the Royal Docks water area, being a large body of still water and not capable of being recycled by flushing. In addition, the land area adjoining the dock water lies at just above or below the impounded dock water level and cannot, therefore, discharge by gravity into the dock water.

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Pumping Stations

Two pumping stations have been built and are connected independently to the foul and surface water sewerage systems. The Tidal Basin Pumping Station, designed by Richard Rogers Partnership, is located on the north-west of the Royal Victoria Dock and pumps surface water to the River Thames via gravity mains and with a discharge capacity of 8 cubic metres per second. The station has been handed over to Thames Water Utilities.

Foul water is pumped via the North Woolwich (Store Road) Pumping Station, which is located in the south-east of the Royal Docks area. This pumping station, designed by Nicholas Grimshaw & Partners, was constructed under a joint venture between the Corporation and Thames Water Utilities. The flow from the station is directed through rising mains to the Thames Water Northern Outfall Sewer which then discharges to the main Thames Water Treatment Works at Beckton. The North Woolwich Pumping Station is more complex than the Tidal Basin Pumping Station in that it has three separate and specific functions. The first is to pump sewage flows from developments in the Royal Docks. The second is to pump a redirected combined sewage flow, arising from the existing communities to the south of the Royal Docks area - Silvertown and North Woolwich - previously served by an old pumping station at Barge House Road and operated by Thames Water. The third function is to deal with excess incoming flows from the existing combined sewerage systems under storm surcharge conditions, which discharge flows via storm overflow gravity mains to the River Thames. The capacity of this station under normal operating conditions is 2.4 cubic metres per second and under storm surcharge conditions can pump at the rate of 4.8 cubic metres per second discharging the excess flow to the River Thames, via the gravity mains. Surface and foul water discharges are conveyed to the two pumping stations via tunnels varying in size from 1.8 metres diameter to 2.4 metres diameter laid at depths down to 15 metres below surface level. The total length of tunnels within the Royal Docks connected to the pumping stations is 10 km with an additional 3 km of trench constructed sewers forming the upstream and shallower lengths. The alignments of this sewerage as far as practicable, have been selected to maximise development areas so as to create flexibility in future development layouts and to minimise encumbrance on building layouts.

The depths of the tunnels have been influenced by the need to link the north and south side development areas below the dock water bed and also to satisfy hydraulic requirements in relation to the areas being drained and the distances to the pumping stations.

Tunnelling has been carried out using a range of tunnel boring techniques, through a variety of different strata, including the Flood Plain Gravels, Woolwich and Reading Beds, London Clay, Thanet Sands and Chalk. Tunnels have been constructed by pipejack and segmental construction, to suit the variability of ground conditions encountered. The tunnelling was not without disruption and was affected in different ways. In one case, siltstone at the base of the tunnel drive caused the buckling of the tailskin of the tunnel boring machine and caused difficulty in maintaining direction of the machine and line of the tunnel. The resulting effect of this was to complete the work after some delay to progress. Considerable additional cost was incurred and compressed air working, following the removal of the damaged tailskin, was required.

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On another drive, passing under the western end of the London City Airport, the tunnel boring machine settled, causing a termination of tunnelling at this location as the machine became lodged. The drainage system, as a consequence of this problem, had to be redesigned and constructed as an alternative alignment to meet the future drainage requirements for development. The shell of the trapped machine remains buried with all the removable internal parts taken out.

Despite some of the difficulties encountered, due mainly to the variability of the ground conditions encountered, the Royal Docks is now fully serviced with trunk sewerage facilities. Negotiations to transfer the sewerage system to Thames Water Utilities are in hand and it is anticipated that this will occur during 1998.

The principal consulting engineers involved in the design of the sewerage and drainage network in the Royal Docks were Sir William Halcrow & Partners and the London Borough of Newham. The major contractors were Miller Civil Engineering, Nuttails, Streeters and Donelan.

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Strategic Services

The strategic services comprise the public utilities equipment, which include within the items provided, the trunk water and gas mains and ductwork through which cabling may be drawn for electricity supplies and telecommunication cables by the respective service providers. These might include the regional electricity company and telephone/cable companies. To service the Royal Docks area, the route of the services generally follows the peripheries of the Royal Victoria Dock, Royal Albert Dock/south of the King George V Dock area in the form of two circular routes joined at the Connaught Crossing to create a figure of eight circuit, combining at this intersection to create a maximum service provision and flexibility of operation for the principal development sites. All the services are kept together in a single corridor, where possible, to minimise the impact of the corridor on developable areas. The general width of services in the corridor is maintained at around 6 metres.

The water mains are connected to external supply mains at the periphery of the area and are generally interconnected with two way feeds to maintain security of supply. Gas mains are connected via two gas governors, positioned at the east and west extremities of the Royal Docks and are also linked to a Pressure Reduction Station at Connaught Crossing. This station is fed by a high pressure primary main, bringing gas from outside of the core area.

Telecommunication cables include British Telecom and Cable & Wireless links, comprising a mixture of copper cables and fibre optic. The development of fibre optic technology and increasing adoption of its use has modified the requirement for ductwork laid in the ground. The original proposals for supply in the late 1980s, demanded upwards of 18 to 24 ducts for copper cable to be laid, in order to accommodate the number of lines required for anticipated development. Future provision of ductwork, where not yet provided, will reduce in quantity to reflect the current technology of fibre optic cable connections.

As regards electricity supply, a base shortfall in primary supply was identified at the planning stage in the late 1980s. This shortfall was established on the level of development proposed and associated demand for electricity.

Although there had been decline in riverfront industry, only 30 megawatt (mw) surplus capacity could be made available from the local substations to supply development in the core area. The shortfall in supply, however, of 140mw had been identified at the planning stage, which at that time would have involved a contribution by the Corporation of £20 million to procure a supply via a new primary substation to be located at the eastern end of the core area. This large cost would be offset by rebates, thus reducing the large capital contribution. However, the means of achieving the rebate depended on power consumption being achieved within an agreed time frame. This method assumed development to occur during a specific period following construction of the substation. The risk of not achieving development within the prescribed time frame meant that the Corporation would forego the rebates.

The decision was taken to defer the substation project as a consequence of the downturn in development in the early 1990s, which vindicated this action. However, although the level of development may not, in the current development strategy, be quite as dense and consumptive of power as perhaps considered previously, there will still be a requirement to reinforce electricity supply for the development proposals.

The current approach to this problem is being pursued via alternative energy solutions to manage demand on a more economic level. Combined heat and power plants are being promoted together with an alternative electricity provider.

The principal consulting engineers involved in the design of strategic services in the Royal Docks were WSP Graham Development Ltd. Major contractors were Nuttall, Peter Birse Ltd, May Gurney and Co. Ltd, Cementation Construction Ltd and Norwest Hoist Construction Ltd.

John Barratt C.Eng., M.I.C.E.
Senior Engineer
W.A. Fairhurst & Partners

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Geoenvironmental Issues

The correct awareness of geotechnical and environmental issues has been a central factor in the development of Docklands. The formation of the LDDC gave an opportunity to undertake a systematic appraisal of the regional conditions to provide support to its redevelopment. The centralised approach of regional appraisal contrasts to the usual situation where such factors are restricted to specific and often relatively short term aspects of each engineering project. The LDDC, aware of the importance of a comprehensive understanding of the ground conditions within its area included geotechnics and environmental engineering geology as a central function within the renewal procedure and retained Dr A F Howland of A F Howland Associates to advise on such matters.

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The Geological Setting

The Docklands area lies on part of the flood plain of the River Thames within the geological province of the London Basin.

The availability of some 5,500 borehole records collated in the Docklands area allowed a revision of the local geology and in particular demonstrated that the large structural dislocation of the Greenwich Fault did not cross the area, as traditionally understood to be the case. The principal geological units of the area are shown in Table 1. These are gently folded so that subsequent erosion has caused various of the units to be present in different parts of the region (Figure 1).

Water well records show the Chalk is approximately 200 metres thick. It is a weak limestone characterised by a whiteness and purity. It forms the main aquifer of the London Basin.

The Thanet Sand is the oldest of the sediments which infill the London Basin. It lies unconformably on the Chalk and in Docklands is about 16 metres thick. In an unweathered state the Thanet Sand has a noticeable green colour, due to the presence of the mineral glauconite, but on weathering changes to a pale yellow brown. It comprises a quartz sand over most of its thickness although minor fractions of clay are found, and occasional thin clay laminae are present. The basal layer of the Thanet Sand is called the Bullhead Bed and is characterized by dark green rounded flint pebbles in a silty clay matrix.

The Woolwich and Reading Beds rest unconformably on the Thanet Sand and overstep them to the west of London to lie directly on the Chalk. They have a similar thickness to the Thanet Sand but form a much more varied sequence. In Docklands seven distinct facies have been identified which reflect the variability of the environment at the time of deposition.

After the Woolwich and Reading Beds a deep water marine environment developed across south east England which resulted in the deposition of the London Clay. Over its greater thickness the London Clay is a dark grey or purplish grey fissured clay with varying proportions of silt and some sand. On a regional scale, there is evidence that the coarse fraction increases towards the west in the direction of the source of sediment supply.

The formations of the solid geology are overlain by much younger superficial materials of Quaternary age which can be separated conveniently into the Thames Gravels and Alluvium.

The Thames Gravels form a distinctive suite of siliceous sand and gravel which extend throughout the middle and lower Thames valley. They were deposited during the colder phases of the Pleistocene under braided conditions following episodic periods of high stream discharge and can be separated into a series of local terraces.

After the last glacial period an overall rise in sea level allowed the deposition of alluvial muds and silts with subordinate and locally extensive peats across the present flood plain of the Thames. This deposition has continued to the present day. In Docklands the present distribution and condition of the alluvium has also been markedly influenced by the effect of man in the historical past. Across much of the urbanized parts of the flood plain the alluvium has been surcharged by made ground placed above it, or has been partly or completely excavated.

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Contamination

The previous use of the Urban Development Area (UDA) means that it is potentially contaminated by chemical pollution. The effects of such contamination are usually permanent, or at least very long lived so that even where there is no evidence of the original cause of the contamination the problem can be sufficiently severe to represent an immediate or long term hazard to human health, to vegetation or construction materials.

The source of the contamination is related invariably to human activities and can arise from a variety of causes so that the development of most sites has not been possible without adequate reference to the possibility of pollution being present. A detailed understanding of the condition of this is essential if a remediation strategy which would allow safe development could be adequately assessed or correctly formulated.

LDDC commissioned a Register of Historic Land use from A F Howland Associates. This had similarities to the philosophy of the register of contaminating use then proposed under section 143 of the Environmental Protection Act, but took the principle further in that, not only was the presence of a contaminating use established but, the history of the site was also recorded. This was supplemented by three other systems which dealt with the data collected from within the area. Together these have provided a systematic approach to the assessment and appreciation of ground conditions able to deal with areas of even gross contamination. A number of treatment programmes have been instigated by LDDC and it has also overseen others by virtue of its powers as local planning authority.

The remedy which may be necessary for any situation is related to the sensitivity of the proposed end-use. In broad terms the options fall into one of three categories:

• removal and replacement,
• treatment, including;

~ physical (solvent leaching, flotation etc.)

~ chemical (oxidation, hydrolysis, neutralization etc.)

~ thermal (direct heating, steam stripping etc.)

~ microbial (selected microorganisms, vegetation etc.)

~ stabilization/solidification (cement or resin based systems)

• containment.

Removal and replacement is by far and away the easiest option. It eliminates the problem in a simple and easily understood way. It does however, suffer from the scale of works that may be necessary to remove significant amounts of contaminated soil from any one site. Removal and transport of the material must be strictly controlled and it must be disposed of within current legislation. The disposal of contaminated material can only be to a licensed site and any such disposal reduces a finite capacity of the disposal resource.

Treatment of contaminated material has scientific elegance but suffers in that no single system is able to deal with the full range of contaminants which may be found on any one site. In fact the mix of substances may affect or reduce the effectiveness otherwise achieved by some processes. Unless a single suite or family of chemicals is present, as may be found after contamination by a single event such as a spillage, then a complex series of procedures may be necessary. The time required by some of the processes can also be lengthy so that the need to protect the site during the treatment process may be as great as if the contamination was left in place. Finally, residual contamination on complex sites often means that subsequent removal or containment may still be necessary.

Containment of the polluted material ensures that contact with it, and any migration of it, is prevented. The procedure often relies on a surface capping to provide a physical barrier between the end user and the contaminated material. The thickness and type of barrier is determined by the proposed end use. Where there is a concern that migration from the site may occur a perimeter barrier can be installed. However, if migration is likely, the principal migration pressure will result in a downward movement and the installation of such barriers below sites with historical industrial contamination is not possible without the initial removal of the contaminated soil itself.

In Docklands many sites have been developed with traditional residential housing on areas where contamination has been proved to be present. In all cases the approach adopted has been for containment. Two prime examples are the Winsor Park Estate in Beckton and Thames Barrier Park, Woolwich.

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Hydrogeology

Two aquifers have an influence on the hydrogeology of Docklands. A lower aquifer comprises the Chalk, together with the overlying Thanet Sand and more sandy basal units of the Woolwich and Reading Beds, and an upper aquifer consists of the Thames Gravels. Over part of the area these are separated by the relatively impermeable London Clay or the cohesive units of the upper units of the Woolwich and Reading Beds, so that the lower aquifer is confined and the conditions in the two are unrelated. Over the remaining part of the area the Thames Gravels lie directly on the lower aquifer such that it becomes unconfined and there is a resulting hydraulic continuity between the two.

In a natural state the hydrogeology of the area has a stability which is a function of both the local and regional geology. In the historical past this natural balance has been upset by the influence of man (Figure 2). Groundwater abstraction in central London during the past 200 years has caused a cone of depression up to 85m deep which spread into the Docklands area (Figure 3). By the 1960's the piezometric surface in the lower aquifer fell from Ordnance Datum south of the Thames at Woolwich, to -8 metres OD on a line which crossed the Royal Docks and the southern Isle of Dogs and deepened rapidly westwards to -60 metres OD through Wapping. A general rise in groundwater has been recorded since the major abstraction ceased. This is also evident in the Docklands area where the piezometric surface in the Southwark area has risen at up to 1.2 metres/yr, although this has possibly been enhanced by leakage from the Docks system. In the east of the Docklands area the groundwater appears to be in equilibrium with the natural situation, although again leakage from the docks has a marked local influence.

The hydrogeology of the area is presently in a state of transition and will vary within the timescales of modern development. Nonetheless, there remains a basic relationship between the various controlling factors to allow an understanding of the overall situation.

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Thames Barrier Site

The Thames Barrier Park forms a plot of land of 9 ha. which lies adjacent to the River Thames. It lies in a stretch of land along the river frontage which has had various heavy industry for about the last 150 years. The site and immediate adjacent areas have had a variety of industrial activities which include:

• rubber works
• telegraph works
• petroleum distillation plants
• manufacturers of treated timber, including

~ production of creosote oils and

~ other tar products

• chemical works manufacturing

~ oleum

~ sulphuric acid

~ hydrochloric acid

~ alkalis and

~ chemical fertilizers

~ "specialist" chemicals'

• Dye works
• Tar refinery producing -

~ phenols and cresols

The Ordnance Survey map of 1893 shows the intensity of industrial activity on the site (Figure 4 - 152k) . None of these structures are present today. Some of these were tanks and reservoirs and therefore are the likely sites of significant infill.

Initial remediation of the site involved the removal of mass concrete substructures and draining of buried tanks and smoothing of the land profiles. The concrete was crushed and graded to form a protective layer to the site while the final development layout was determined. Once this was finalised the existing crushed concrete was stripped and further cut and fill undertaken to form the required contours. Following removal of any further visibly contaminated material the crushed concrete was replaced and a capillary break layer laid above this. This was protected by a geotextile filter before the final depth of subsoil and topsoil was spread on top.

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Winsor Park Development

Beckton housed one of the largest gasworks based on coal carbonisation in Europe. It produced gas from 1870 and finally ceased operation in 1968 (Figure 5 - 150K) . It also had a large chemical by-products works situated adjacent to the main production area. The area south west of the works acted as a marshalling yard for the storage of coal and coke. It also accumulated large amounts of waste from the works.

A succession of investigations showed that contamination was present over much of the area including various liquors and tarry products. Surface water ponding on the area was also shown to be highly acidic and contaminated with oil-tar material.

The waste products were to depths of 4 metres and included substances which are both toxic and carcinogenic even at very low concentrations. In addition many of the contaminants are also corrosive and therefore damaging to construction materials.

The LDDC became involved in the site through a compulsory purchase order. This went to public enquiry at which the LDDC argued that the area should be developed for housing and that the contaminated nature required a total and managed approach to the treatment of the area as a whole. It was argued that this would optimise the resources available and lead to a better control of the attendant operations than would otherwise be possible if the total area was developed on a piecemeal basis.

Consideration of the whole site would also allow a greater flexibility of approach to its reclamation. The level of contamination classified the material as special waste under the then Control of Pollution Act 1974. The large volumes of material involved meant that its total removal and disposal was impractical.

Treatment of the material was largely impractical because of the variability of material present and timescales required for the completion of the process.

It was concluded that the only viable approach to the reclamation of the area was by a containment system (Figure 6 - 63k). This had the advantage that no material needed to be removed from site and the system was instantly available once the engineering works were complete. In view of the degree of contamination it was felt that the barrier should consist of a minimum of a metre clean imported material.

Dr AI Howland MSc, PhD, D.I.C. C.Eng.,
FIMM CGeol FGS
A.F. Howland Associates 

Note by Webmaster:  For more on the work of A.F.Howland in Docklands visit the company web site at http://www.howland.co.uk

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Construction of the Docklands Highways

Click here for Location Plan - 182k

London Docklands is now served by the Docklands Light Railway (DLR), a network of new four lane highways, improved roads, existing roads including a major trunk (the east-west A13), two tunnels crossing the Thames - the Blackwall and the Rotherhithe Tunnels - London Underground in the west, an airport, ever improving bus services, British Rail and construction work nearing completion on the Jubilee Line Extension, scheduled to open in Spring 1999. 83,000 people live in the area and 85,000 work here.

Seventeen years ago the area was served by the one main road - the A13 - the two Thames tunnels, and a series of local roads skirting high dock walls and, on these roads, an infrequent bus service. Local minicabs played a major role in moving the 39,400 residents to and from the London Transport network, mainly at Mile End tube station on the Central and District lines. The working population was 27,200 and declining.

When the LDDC was set up in 1981 with the task of securing the lasting physical, economic and social regeneration of the area it was faced with large areas of land that nobody wanted to buy, no new private investment and nothing to trigger growth. The housing was predominantly rented, mostly by the local Councils, deteriorating and quite often considered undesirable and, more importantly, the outdated infrastructure needed major public investment.

It was recognised from the outset that the area could only generate new opportunities if it was opened up and access dramatically improved. The challenge was to achieve this by creating a public/private sector partnership and by levering in new investment.

The Corporation was given planning control powers; powers to buy and sell land; and an annual grant voted by Parliament. It was not to be a housing authority, a highway authority nor an environmental health authority. The apparent impotence imposed by the lack of these powers, particularly in building roads, required the LDDC to liaise in detail with the relevant boroughs and other authorities.

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In April 1982 part of the area - on the Isle of Dogs - was given Enterprise Zone status with all the inherent financial incentives for developers and investors. Within two to three years low rise buildings and light industrial workshops had been attracted. The transport needs were to be met by a series of new and improved local roads together with the Greater London Council's (GLC) Docklands Northern Relief Road, a good bus network and a light rail system, the DLR, which would operate on new and old viaducts previously used by trains servicing the docks. The decision to build the DLR (from Tower Gateway to Island Gardens and up to Stratford) was taken in 1982. Construction commenced in 1984 and the railway opened to the public in 1987. Roads serving the Enterprise Zone were built by 1984 and a two lane road, parallel to and south of Poplar High Street was completed by 1986. The latter had in fact been devised as a stage of the Docklands Northern Relief Road by the GLC in the mid 1970s.

As late as 1984 the highest estimate for the level of activity in the Isle of Dogs forecast a maximum of 8 million sq. ft (743,000 sq.m.) of commercial development. However, by 1986 outline approval had been given for a single 12 million sq. ft (1.1 million sq.m.) development on Canary Wharf in the heart of the Enterprise Zone and other large scale proposals amounting to a proposed 40 million sq. ft (3.7 million sq.m.) were being considered on the Isle of Dogs. The property boom of the mid 1980s and the tax advantages of the Enterprise Zone saw a fourfold increase in the development projections for the area within a short timescale.

In the light of the enhanced development expectations, the Corporation formed a transport strategy with the following key objectives:-

• to provide good access to the development areas from the major road and public transport networks;
• to reduce the barrier effect of the River Thames and the River Lea and improve links within Docklands;
• to provide an integrated public/private transport network with the capacity sufficient to meet the proposed increased demands from new developments, but with the emphasis on public transport;
• to improve local transport facilities and access, for existing and new residents, to employment and leisure facilities.

An extension of the DLR to Beckton in the east was proposed, in parallel with the extension to Bank in the west, which was to be jointly funded by Canary Wharf developer, Olympia & York, and London Transport.

To integrate with the DLR and other public transport modes, the Corporation initiated a strategic highways network, comprising ten major schemes running west to east through Docklands, known as the Docklands Highways.

For a full description of the Corporation's transport strategy see the LDDC's publication "Starting From Scratch".

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Docklands Highways

The first three schemes constitute in effect a variation on the Docklnds Northern Relief Route which was incorporated into the Docklands Highways programme to ensure that it was built as the abolition of the GLC in April 1986 had further placed it in jeopardy. Proposals for the Docklands Highways were approved by the LDDC Board in mid 1986. Just over three and a half years later most of the major schemes were on site and all had been completed by May 1993 at a total construction cost of some £570 million.

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Limehouse Link

The 1.8 km four lane tunnel links The Highway, at the junction of Butcher Row and Narrow Street, to Westferry Road and to North Quay on the Isle of Dogs. The road passes under the north side of Limehouse Basin, turning south to pass underneath Limekiln Dock and Dundee Wharf and joins with Westferry Road and the Poplar link. The scheme also included the widening of Westferry Road from Westferry Circus to West India Dock Road. Construction started in November 1989, and the road opened in May 1993.

Contractor: Balfour Beatty AMEC Joint Venture
Consulting Engineers: Sir Alexander Gibb & Partners

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Poplar Link (Aspen Way)

Built in phases over two and a half years the Poplar Link upgrades a road already built along this corridor by the Corporation. The west side of the scheme included improvements to West India Dock Road, along with the realignment of the junction with the A13 Commercial Road. The 1.4km varies from a four to six lane road and its alignment continues from West India Dock Road, eastwards across the north of the Isle of Dogs to Prestons Road Flyover. A major new roundabout at Prestons Road links with the East India Dock Link (Aspen Way east). The full scheme opened in May 1993.

Contractors: Percy Bilton plc,.
Roadworks (1952) Limited,
Mowlem South-East
Consulting Engineers: Mott MacDonald

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East India Dock Link/Prestons Road Flyover

A dual carriageway road, about 1 km long, links Prestons Road roundabout with East India Dock Road (A13), at the Canning Town Flyover. Developments are served by roads connected to a new roundabout at the southern end of Leamouth Road, which in turn links to the Lower Lea Crossing. The northern end of East India Dock Link, connecting with the A13 by a cut and cover tunnel under East India Dock/Leamouth Road, has been upgraded to dual carriageway, including the new junction with the A13. An east-west flyover has been built at Prestons Road roundabout connecting East India Dock Link with Poplar Link. Construction of the tunnel and flyover started in November 1990, with the scheme opening to traffic in May 1993. This scheme only completed the westbound bore whilst the eastbound is due to be completed by the Highways Agency as part of future A13 major improvements.

Contractors: Wimpey Major Projects (Phase 1),
Edmund Nuttall Limited (Phase 2),
T E Beach Ltd (Leamouth Road)
Consulting Engineers: Mott MacDonald

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Canary Wharf Eastern Access (Trafalgar Way)

This 750 metre dual carriageway links the roundabout at Prestons Road to the eastern end of Canary Wharf, via the northern and western boundaries of Poplar Dock. Two bridges span the entrance to Blackwall Basin and across the West India Docks onto Canary Wharf. The scheme was built between August 1989 and November 1990.

Contractor: Taylor Woodrow Construction
Consulting Engineers: Mott MacDonald

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Lower Lea Crossing

This four lane road, approximately 1 km long, connects the Isle of Dogs with the Royal Docks, linking the roundabout at Leamouth Road with a new roundabout underneath Silvertown Way Viaduct. The road includes a bridge over the River Lea. Construction started in February 1990 and the road was opened in December 1991.

Contractor: Norwest Holst Construction
Consulting Engineers: Mott MacDonald

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Enterprise Zone Road Improvements

The distinctive red brick roads built in the Enterprise Zone, which already carry substantial volumes of traffic, have progressively been improved with an asphalt wearing course, new turning lanes, bus laybys and upgraded junctions, and are being repaired after the damage done by the Docklands bomb in February 1996.

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North Woolwich Road

A two lane section of North Woolwich Road, south of the Pontoon Dock, has been widened over a length of approximately 500 metres, with landscaping on the north side to complement the established Silvertown Tramway scheme to the south. Work started in May 1988 and was completed in May 1990.

Contractor: Fitzpatrick & Son (Contractor) Ltd
Consulting Engineers: London Borough of Newham

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Connaught Crossing

A new four lane north-south road, about 900 metres long, has been built between Royal Victoria Dock and the King George V and Royal Albert Docks. It links North Woolwich Road and Factory Road in the south, to Connaught Road and the Royal Albert Dock Spine Road in the north, with roundabouts at both junctions. A third roundabout links east to Connaught Road and London City Airport and west to the Pontoon Dock area. The road crosses the dock cutting on a swing bridge and was built in several stages, starting August 1987. The crossing opened to traffic in February 1990.

Contractors: Norwest Holst Construction (Phase 1),
Peter Birse Ltd (Phase 2)
Consulting Engineers: Sir William Halcrow & Partners

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Royal Albert Way

The 1.8 km Royal Albert Way is the major east west link between the Connaught Crossing and Royal Docks Road. The dual two lane road runs south of and parallel to Strait Road along the full length of Royal Albert Dock. Intermediate roundabouts serve the area and, in two cases, allow for integral stations on the DLR, Construction started in March 1988 and the road opened in April 1990.

Contractor: Edmund Nuttall Limited
Consulting Engineers: Frank Graham & Partners

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Royal Docks Road

This predominantly dual carriageway two lane road, about 2km long, extends from the A13/A406 (South Woodford to Barking Relief Road) junction to a new roundabout around the Gallions Pumping Station. An extension from this roundabout serves the Beckton Gas Works site and the DLR depot. Work started in June 1986 and the road opened in October 1989.

Contractors: John Laing plc (Phase 1),
Percy Bilton plc (Phase 2)
Consulting Engineers: London Borough of Newham

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The Limehouse Link - Engineering Case Study

Location Plan - 203k
Longitudinal section of Limehouse Link showing geology - 55k
Cross section of Tunnel and Eastern Services Building - 48k
Base Construction - 44k

Limehouse Link is the critical link in the highways network, providing the psychologically important direct connection to the City of London and on to the West End. As well as improving access to the surrounding East London strategic road network, it has brought significant traffic relief to Limehouse which, combined with traffic management measures, secured improved environmental conditions for local residents and future development.

LDDC studies identified a number of options to build the link between the Isle of Dogs and the City. The scheme built is a two lane dual carriageway with an underground junction at Westferry Road. The alignment at the western end is determined by the presence of the Rotherhithe Tunnel approach ramp, from where it curves along the northern edge of the Limehouse Basin. Here the tunnel depth is dictated by the navigable depth required for the connection between Regent's Canal and the Thames. From here the route runs through an open area, Ropemakers' Fields, between existing housing; it then crosses under Limekiln Dock. The tunnel then widens to accommodate slip roads leading to and from Westferry Road and Canary Wharf. It continues under the DLR and West India Dock Road before rising to the surface to connect with the Poplar Link. The total length is 1.8 km, with 1.5 km in tunnel; the roof is generally 6 - 8 metres below ground.

Planning permission for the road was granted in July 1988 after the Secretary of State for the Environment decided not to call in the planning application. A public inquiry into the Compulsory Purchase Order, needed to acquire necessary land which the LDDC had not been able to obtain by agreement, was held in October 1989 and lasted four weeks.

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The Accord

The co-operation of Tower Hamlets, as housing authority and highway authority for the area, was essential, and after lengthy negotiations the LDDC signed an Accord with the Borough Council in an effort to minimize disruption for people living along the line of the road. In return for the Council's co-operation and support for the Docklands Highways schemes, the LDDC undertook to provide replacement housing and to refurbish existing accommodation for those tenants directly affected. The LDDC paid for 301 homes to be refurbished, 556 households were moved to new housing association homes or refurbished council flats; and secondary glazing was provided in 338 homes to alleviate noise during construction. In addition, the LDDC provided a £35 million package of social, economic and community developments to benefit residents of Tower Hamlets.

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Design of the Link

Consultant, Sir Alexander Gibb & Partners, was appointed by the LDDC in 1987 with a brief to confirm the route alignment, to determine the scope of the site investigations needed, to identify construction methods to minimize environmental impact, to design the structure and services and to prepare tender documentation. This was to be done to a fast-track programme allowing less than two years to tender stage. The tunnel box was to be designed to carry loads resulting from future development overhead.

There was no precedent for construction of this type of tunnel in the variable ground conditions of East London. Design began with an information gathering exercise to collect published data on ground conditions, and to find historical information on earlier construction in the area. Construction records could not be found for many structures alongside the road, so structural surveys were carried out on buildings and structures within 40 metres of the tunnel. Risby House, a Ronan Point type residential tower block, was found to be in a critical condition already. The tenants were rehoused under the Accord and it was demolished.

Ground conditions were complex with made ground overlying Thames Gravel, London Clay, Woolwich and Reading Beds, Thanet Sands, and chalk bedrock. Structural design of the tunnel was dictated by the difficult water-bearing strata. Geotechnical investigations were delayed by access problems, so the initial design was carried out to provisional parameters. The investigation subdivided the Woolwich and Reading Beds into five sub layers with differing properties. When final results became available in August 1988, the design parameters turned out to be more conservative than had been assumed, requiring extensive redesign of the tunnel walls during the tender period and initial construction period.

The design adopted a plain rectangular tunnel box for ease of construction, with twin bores 10 metres wide separated by a central wall. A width of up to 22 metres was needed to accommodate the slip roads for the underground junction. The box was 7.8 metres high, providing clearance for services overhead and depth for service trenches below the road surface level. Connections between the external walls and roof and floor slabs were pin jointed with dowels for temporary support of the slabs during construction. These were to be supplemented by skin (shear) walls constructed inside the tunnel box after casting of the base slab. Computers were used extensively in the structural design.

The tunnel has a design speed of 60 km/h, with a medium centreline radius of 189 metres and gradients on the approach ramps of up to 6.8%. Development surcharge load was fixed at 80 kN/sq.mtetre, equivalent to a four-storey building.

Ground conditions and the relatively shallow tunnel depth dictated that construction should be by cut and cover methods. In order to minimize the construction corridor width and ground movements, 'top down' construction was specified.

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Envisaged construction sequence

Diaphragm walls would be built on each side of the tunnel, to 4 metres below base slab level, to form the external walls of the tunnel box.

Excavation would be carried out down to roof soffit level, and the diaphragm wall upstands would be propped where excavation exceeded 3 metres. The roof slab would then be cast.

Excavation under the roof slab could then continue through openings left for this purpose. Props would be installed at mid-bore before excavation continued to slab soffit level. The slab would be cast and the box would be completed by casting the central and shear walls. Finally, backfilling to the original ground level would be completed over the roof slab.

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Services

The tunnel required a wide range of services, including 11 kV electrics, closed-circuit television, traffic management, radio communications and variable message road signs. Services are controlled by a computerized system linked to the operations control room and the Metropolitan Police Control at East London Traffic Control Centre.

Ventilation extract fans, power distribution and other services are housed in three service buildings framed in reinforced concrete, housed over the tunnel portals and a fourth off-line building east of the Limehouse Basin.

Design of the ventilation system was complex because of the varying width of the tunnel bores and the slip roads located part way along. The design requirement was to keep concentrations of carbon monoxide and diesel smoke within acceptable limits under all operating conditions. In addition, a minimum air flow speed of 4 metres per second was required to be generated for emergency control of smoke and heat. A longitudinal ventilation system with jet fans mounted along the roof soffit was adopted to propel air in the direction of traffic flow. Computer modelling took into account factors such as external wind speeds of up to 3.5 metres per second.

At each portal, axial fans extract air from beneath the tunnel roof and discharge it through high level vent stacks. The system is controlled automatically by carbon monoxide analysers and visibility monitors.

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The Contract and Alternative Design for the Limehouse Basin

Civil and electrical/mechanical works were let as a single contract because of the complexity of interfaces between them. Because of the complexity of the project a critical path analysis of 400 significant activities was carried out to determine a 48 month construction period. The form of contract used by the LDDC was the Property Services Agency's GC Works 1 amended to include a clause on unforeseeable ground conditions with Sir Alexander Gibb & Partners as superintending officer. Tenderers were invited to submit alternative designs.

A joint venture of Balfour Beatty and AMEC submitted a proposal to build the section through the Limehouse Basin bottom-up within a cofferdam, rather than top-down. This offered a £4 million saving and, more importantly, a six month reduction in the contract period. This alternative could only be used in the Limehouse Basin area because of the proximity elsewhere of residential properties and the noise and vibration of cofferdam installation. The tenderer was able to satisfy concerns about ground movement, particularly adjacent to the DLR viaduct, and the Balfour Beatty AMEC Joint Venture was awarded the contract in October 1989 and construction commenced in November 1989.

Robert Benaim & Associates were commissioned by the joint venture to design the permanent works for the alternative section and this was checked by Sir Alexander Gibb & Partners. The contractor designed temporary works in house and these were checked by Benaim. Close co-operation between the joint venture and Benaim allowed further modifications to the design of the tunnel box, giving cost. and programme benefits and improved buildability. These prompted many of the alternatives proposed when value engineering was introduced later in the contract. Among these, the base slab was designed to incorporate the road construction make up, main surface water drainage and four service trenches.

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Environmental Constraints

During construction, noise and vibration levels were limited under a Section 61 of the Control of Pollution Act 1974 by an agreement negotiated with the London Borough of Tower Hamlets by the LDDC. Some properties had to be temporarily vacated. Because of the proximity of residential areas, most construction activities were restricted to between 8 am and 6 pm. However, some work was allowed to continue on a 24 hour profile with the obvious imposition of a lower noise limit during the night. For environmental reasons, and to minimize traffic congestion, most materials and equipment were delivered and removed by river, via a specially built 200 metres long temporary wharf at Dundee Wharf. This handled 3.5 x 106 tonnes of materials and spoil during the contract.

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Concrete delivery

Of the 310,000 square metres of concrete used in the project, 78% was mixed by computer -controlled hatching plant, with a combined capacity of 195 cu m/h at Dundee Wharf. Most concrete was pumped directly from the plant to each pour through 125 mm pipes. Single pump distances of 700 metres were achieved, and stage pumping increased this to over 1,000 metres at rates of 50 cu m/h.

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Contract Variations and Value Engineering

The contract underwent considerable changes, not least the late access to areas on the site and delayed installation of secondary glazing to adjacent residential properties. These held up progress, which led to a variation agreement between the Joint Venture and the LDDC to mitigate the effects. Later, a contract amendment incorporated further variations. These brought about several changes, including additional tunnel work fronts and resources, a review and resolution of delays at 90-day intervals, a lump sum fixed price for the works, and the LDDC assuming the role of superintending officer to bring the client and contractor closer together, with Sir Alexander Gibb & Partners remaining as resident engineer. The most important change, however, was the introduction of value engineering.

Value engineering was introduced in March 1991 by the variation agreement. It enabled the joint venture to propose changes to the design and to benefit from a share of any savings. This allowed delays to be recovered, and overall completion was achieved five-and a-half months early, affording substantial financial savings for both the contractor and the client. Value engineering proposals were developed by the Joint Venture with its consultants, Robert Benaim & Associates and Mott MacDonald. Of 13 major proposals made, nine were accepted. - The following were the main ones:

• Roof slab/base slab:

The very heavy reinforcement content of the roof slab was reduced by shaping it to complement the maximum stresses developed in it. In addition, the road construction make-up and drainage were incorporated into the structural base slab, instead of being added afterwards, removing a major secondary activity from the construction programme.

• Skin walls and columns:

The continuous internal skin wall was replaced by a series of skin columns performing the same structural function but with a 60% reduction in materials.

• Temporary roof slab support:

Modifications to the base slab design and temporary roof slab support allowed the central wall to be built in bays three times longer than originally detailed.

• Eastern services building ground floor support slab:

An additional row of central columns enabled a 2.5 metres deep 22 metres span in-situ slab to be replaced by two 1 1 metres span composite precast beam in-situ 1.2 metres deep, saving 60% in materials.

• The observational method:

Apart from the redesign of the base slab, this was the most significant of the value engineering changes in terms of savings in cost and time. Developed in association with Mott MacDonald, it allowed tunnel props to be omitted. Key factors in the success of the observational method were speed of construction (to take advantage of the short-term strength of the soil), the accuracy and reliability of measurements, and the availability of contingency plans to react to unacceptable events

The original design required temporary propping - by 1340 mm diameter steel tubes at 4.2 metre centres - of the side walls during top-down construction. Props were to be installed above and below the tunnel roof slab and loads in them monitored. As well as hampering excavation below prop level and slowing construction, the original design would have required handling 6450 tonne of temporary steelwork. The observational method allowed this to be reduced to 1550 tonne. However, monitoring of the props above slab level showed that loads were much lower than expected.

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The method was applied in stages. First, the props were installed and loads monitored as excavation progressed below them. They were found to be typically only 10% of design load. The next stage was to change to 'soft props' with a predetermined gap at one end, while monitoring wall convergence. Provided this was within acceptable limits, construction could proceed without props. A number of reserve props were kept near each construction front as a contingency against unacceptable movements.

A maximum total wall convergence of 70 mm was allowed at slab soffit level. The maximum observed movement was 11 mm, and convergence was generally less than 7 mm. The method was applied to all nine construction fronts in the top-down sections of construction and in all cases props were successfully dispensed with after going through the initial stages of using first 'hard' and then 'soft' props. Although difficult to quantify, elimination of the difficulties of handling and working around the vast quantities of steelwork made the observational method safer than the original design.

Value engineering gave rise to major savings in material and contributed greatly to the recovery of earlier delays. But the Limehouse Link's greatest success was due to the close co operation between the client, contractor, and all the design teams involved. Without this, many of the innovations and engineering achievements would not have been realized.

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Running the Roads

With the opening of the Limehouse Link and the rest of the Docklands Highways on 17th May 1993, the LDDC was responsible for managing and operating the 32 km (17 miles) of road, 22 km (12 miles) of which could be classified as major carriageway. This is thought to be the largest privately owned road network in Europe which is accessible to the public.

The LDDC decided to retainresponsibility for the operation of the roads, which would normally have been done by a highway authority, as it wanted to take a proactive role in minimising disruption for residents and incoming companies and to ensure that traffic was kept moving safely and efficiently while developers were constructing the major schemes in the area.

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Controlling Forces

Traffic control can be carried out in a variety of ways, but the LDDC team found that personal contact is the answer even in an area synonymous with high-tech developments.

From the legislative point of view, the Highways Act does not strictly apply to LDDC's roads, although for practical purposes the Corporation acts as a traffic authority not as a highway authority. The Road Traffic Act does however apply, and the provisions of Chapter 8 are administered, along with traffic management in the joint names of the LDDC and the relevant highway authority orders for speed and clearways.

The LDDC operations team consisted of up to 50 people, half of which worked on managing the operation and maintenance of the Limehouse Link and the East India Dock Tunnel, and the others on the remaining highway network including road safety officers or 'white-caps' who constantly patrol the area dealing with minor incidents such as illegally parked vehicles, giving directions and information, manning shuttle working, laying out traffic management equipment, keeping an eye out for areas or items which require maintenance and assisting at accidents and incidents. The team is based in a purpose built building in Orchard Place from where the tunnel is 'driven'.

The accident rate in Docklands is lower than average for the length and type of road but probably greater in variety. There were incidents however, such as the horse which had escaped from the City Farm and was determinedly trotting the wrong way round a roundabout, and a rather less savoury escapade when a jack knifed lorry from a local food processor spilt 30 tons of pigs heads across a dual carriageway.

Procedure for these incidents is fixed and straightforward. All the team members are routinely equipped with safety equipment and five channel two-way radios. The moment an incident is reported it is recorded. Information is recorded on a real time database and the report is generally started there and then. The LDDC team does not confine its services to accidents within its own area though. It has excellent relationships with opposite numbers in the Metropolitan Police, Tower Hamlets, Newham and Southwark and routinely offers assistance if appropriate.

The simple aim had to be to keep the traffic moving which, all things considered, was achieved very successfully with a programme of information and strict enforcement, including the production of a newsletter entitled "Keep The Traffic Moving". This showed drivers where the construction activities and possible delays were.

CCTV cameras cover the approaches to the tunnel and the tunnel itself with sensors in the road surface to measure traffic flow, speed and congestion.

The Limehouse Link is closed regularly for routine maintenance by the team at night, whereas the East India Dock Tunnel is cleaned with lane closures only.

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Considerate Contractor Scheme

With help from the City of London engineers, the Corporation instigated a 'Considerate Contractor' scheme. The construction sites were patrolled by two former police officers, as part of the traffic control team and ensured that the interface between the public and the contractor was safe and clean. Given the amount of construction which took place during the late eighties and early nineties, they proved remarkably effective.

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The Future

The Docklands highway network covered the three Docklands boroughs Newham, Southwark and Tower Hamlets. The boroughs have or are in the process of adopting all the LDDC's roads and the Corporation has progressively handed on its responsibilities in the area since the end of 1994. The exceptions are the Limehouse Link and East India Dock Link tunnels and the connecting dual carriageway, Aspen Way and Prestons Road Flyover, whose ownership will transfer to the Commission for the New Towns, the government agency which takes on all remaining assets and liabilities of the English Urban Development Corporations, including LDDC, from 31st March 1998.

Bob Blyth BSc, C.Eng., M.I.C.E., M.I.N.T.
Partner, W.A. Fairhurst & Partners
(formerly LDDC Chief Engineer)

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River and Dock Walls

River Walls

The LDDC, at its peak, owned some 13 km of river walls from Tower Bridge in the west to Gallions Reach in the east. LDDC found it was responsible for maintaining an effective flood defence at all times, as required under the Thames River (Prevention of Flood) Act 1879, the Land Drainage Bylaws 1981 and the Water Resources Act 1991. The flood level upstream of the Thames barrier is 5.23 metres Ordnance Datum Newlyn (O.D.N.) and 7.2 metres O.D.N. on the downstream side of the Thames Barrier.

The types of the various walls that the LDDC inherited as owners of the adjacent land were varied. They ranged from war damaged and emergency repaired brick walls in the upper pool of London in Wapping to almost non-existent timber walls at Galllions Reach. The walls varied in construction from the earlier mass concrete gravity walls to the relatively modern sheet-piled walls frequently with high level ground anchor supports.

When it became necessary to check the stability of old walls with high level tie-backs or anchors, site inspection often found either the old mild steel anchor rods in very poor condition or in some cases, a minimalistic sign of the original anchor rod was indicated only by rust staining of the soil. Similarly, original timber anchors were sometimes found to have rotten away almost completely. Naturally, this was of great concern to the inspecting civil engineers as these walls were calculated to be instable and required remedial action.

The reason for these material failures could have been either poor original materials or aggressive ground conditions, as the areas adjacent to the river have historically been used for industrial purposes and were frequently contaminated. These contaminants could have attacked the walls and their associated ground anchors. As a consequence, modern rebuilt walls use quality materials with protective coatings. Sheet-pile walls were designed for a safe life-span of 60 - 70 years as required then by the National Rivers Authority (NRA) and more recently the Environment Agency. To achieve these life-spans, the sheet piles were protected with epoxy-coatings applied at the factories, the anchors were surrounded in cement grout or anchor ties were wrapped in dense tape. These protective coatings were designed to extend the life expectancy of component parts of the walls.

During the 17 year life of the LDDC, the Corporation rebuilt many walls predominantly to allow development of the adjoining land such as the residential estates at Maconochies Wharf, Caledonian Wharf and Duggan's Wharf on the Isle of Dogs. Frequently, the new walls were constructed of sheet-piling, some with brick wall facing, many with concrete copings to take the hand railings. All new walls were fitted with timber rendering to prevent damage to the walls by shipping. Figure 1 (102k) shows the walls repaired or built during the LDDC's life at a cost of £12 million.

A major policy that the LDDC pursued whenever it developed land adjacent to the river was to provide a public walkway, thereby allowing people to once again enjoy the benefits of access along the riverside. This has proved to be both environmentally enhancing and particularly popular with the public, who can now walk for miles around the Isle of Dogs and along the river edge in Southwark.

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At the time of the transfer of responsibility from the NRA to the Environment Agency, the LDDC encountered a distinct change in policy on embanking into the river. The Environment Agency's policy now is to not allow encroachment or embankment into the River Thames, which has historically been carried out for centuries. The Environment Agency believes the river is narrow enough and is concerned about the effect of water velocity increases on the breeding beds of fish in the water. This proved particular challenging to the LDDC when trying to repair river walls by the tried and trusted method of driving sheet-piles on the water side of the old river walls. Furthermore, the Environment Agency's policy changed in 1997 away from traditional sheet-pile walls to the much more environmentally friendly method of sloping banks or timber walls and the like, which will promote the growth of the Thames flora and fauna. This was particularly challenging to the LDDC's civil engineers who still managed to design and construct walls with enhanced environmental designs. At Gallions Reach, the new river wall was designed to accommodate the natural growth of the salt marsh, which appears to grow only at this location and level. Parts of the new wall were built at the same level as the old collapsed timber wall, on which the salt marsh was growing in the naturally deposited river silt. The wall then slopes up to the normal levels in front of the existing flood defence wall. Both the Environment Agency and the Ministry of Agriculture and Fisheries complimented the LDDC and its consultants, MLM Consulting Engineers, on this design.

In the latter years of its life, the LDDC implemented a major review of the conditions of its river walls, ready to pass the walls onto new owners. The first phase was the repair of river walls at Arnhem Wharf, Isle of Dogs and East India Dock entrance by Costains and Hermitage river wall, Wapping, by Mowlem Marine at a total cost of £1.89 million.

The second phase entailed new walls and repairs at Blackwall Goods Yard, River Lea by John Martin Construction and Gallions Reach new walls by Jackson Civil Engineers at a total cost of £1.8 million.

The first two phases were the repair or building of new walls because the existing were at the end of their useful life.

The third phase of the river wall contracts was a general contract to repair defects in the remaining LDDC walls. The work was carried out by Tilbury Douglas Construction on 23 different locations at a total cost of £4.0 million using a prime cost contract to allow the unforeseen element of this type of work. This contract proved to be ideally suited to this project with a rapid agreement of the final account as a consequence.

All the LDDC walls were passed on to new owners, knowing they will not need any further work for at least another 25 years.

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Dock Walls

In its lifetime, the LDDC inherited and acquired six dock systems: London Docks in Wapping, Surrey Docks in Southwark, West India and Millwall Docks on the Isle of Dogs, East India Dock and Basin in Leamouth and the Royal Docks in Newham.

Historically, construction of the docks started in 1763 with the Greenland Dock in Surrey Docks, Southwark and construction continued through the years until the King George V Dock was built in 1921. As the docks have been built over one and a half centuries, the style and type of dock wall has varied through the years culminating in 39 different types of dock walls. The Royal Docks in the east, which are the largest docks, have 28 types of walls. The Royal Docks, unlike the other docks, have been artificially raised in height from the surrounding ground by using the excavated material on the surround of the docks back about 61 metres. Therefore, the impounded water level of 4.24 metres is over 2 metres higher than the centre of Silvertown which is located between the river and the docks.

One of the Corporation's first projects in 1982 was the continuation of London Borough of Tower Hamlets partial filling of Western Dock in readiness for the construction of housing. This is part of the former London Docks. During the early phase of the project, hundreds of old clay pipes, together with oyster shells were uncovered at the back of the dock walls. These were attributed to the Napoleonic prisoners of war who were used to dig out the docks at the time of original construction in 1805. The London Docks had a monopoly on rice, tobacco, wine and spirits whereas the West India Docks, opening in 1802, had a 21 year monopoly on Caribbean trade for cargoes including sugar, rum, coffee and mahogany. The West India Docks had room for 600 sailing ships. The East India Docks were opened in 1806 where tea, spices, precious metals, silk and porcelain were unloaded. South of the river, the Surrey Docks opened between 1807 and 1811 to handle timber from Scandinavia and the Baltic Ports.

In the late 19th and early 20th century, longer and deeper docks were built to meet the demands of the empire trade, i.e. Royal Victoria Dock (1855), Millwall Docks (1868), the Royal Albert Dock (1880) and lastly King George V Dock (1921) where great liners berthed.

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During the blitz of the second World War, London Docklands became the most heavily bombed civilian target in Britain. This made extensive modernisation and rebuilding imperative in the 1950s and 60s when some of the docks were repaired generally on an ad hoc basis. In the Royal Docks, the LDDC was responsible for some 16 km of dock walls which artificially held the dock water at a level higher than the surrounding areas. It was therefore paramount that the Corporation's engineers were aware of the structural stability of these numerous types of wall within the Royal Docks. Surveys were carried out to investigate the types and stability of the walls together with estimates of their useful life.

On the north side of the Royal Albert Dock and the Royal Victoria Dock, great lengths of the dock walls were overhung by false quays. Detailed surveys of these false quays were also carried out and estimated costs of the repairs were prepared, which in some cases were handed on to respective developers as a liability, which should be considered in their business plans. As an aid to regeneration in the late 1980s, most of the structural concrete of the suspended quay on the north side of the Royal Albert Dock was repaired by the Corporation. Western Gateway on the northwest edge of Victoria Dock was also rebuilt together with associated landscaping. Parts of Pontoon Dock which were particularly decrepit and unstable were replaced with new sheet-pile walls. The LDDC engineers concluded that if, by some accident, the water was allowed to drain out of the Royal Docks, approximately one-third of the dock walls would suffer some sort of collapse or movement which would cost millions to repair. When the new lock gates were fitted in the King George V Dock, the only access to the Royal Docks, fail-safe systems were put into place so that the docks can never be drained. On very high tide when there are run-ins from the Thames into the docks, it is the policy of the Royal Docks Management Authority (RODMA) to have water wardens on standby to make sure that the gates close properly when the river water recedes. This is paramount for the integrity of the Royal Docks, West India and Millwall Docks.

Gavin Ridding BSc, C.Eng., M.I.C.E.
LDDC Senior Engineer

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London Docklands Water Quality

The LDDC area covers 1,700 ha. of which more than 170 ha. are water. It has over 90 km of water frontage, most of which is seen as a positive asset in regeneration of the area. The size and type of water spaces range from small basins to the three huge Royal Docks, the longest 2.4 km long. Several are linked by canals and locks, whereas others are now isolated, and access to the river is limited. The principal water areas are show in Figure 1 (52K) and Table 1 indicates average depths, areas and volumes of the dock systems.

Against the prevailing economic advice and opinion of the time, the LDDC made the important visionary decision to retain the remaining water areas, thereby adding almost 10% of open space to the area. In the years preceding 1981, several of the docks were filled in the belief that the newly created land was of more value than the water. Yet it is the water which today makes Docklands such an exceptional place. The water space is being integrated with the developments while the best of the dock buildings and infrastructure are being brought into new, different and active use.

The requirement of the dock waters in their former use was basically to support shipping activity. The movement of the vessels and the frequent locking and impounding operations meant that the water was kept moving and had a relatively low residence time in the docks.

The waters are now 'open spaces' within the UDA and as such, in addition to their aesthetic contribution to the area, are used for a wide range of sports and leisure activities. Those which take place on a regular basis include sailing, windsurfing, canoeing, rowing, angling, sub aqua, dragonboat racing, water-skiing, wet biking and jet skiing.

In addition there is a marina at South Dock in the Surrey Docks with 371 berths, and elsewhere in the docks mooring for historic vessels and visiting craft. Also the large locks at the eastern ends of the Royal Docks and the West India Docks and Millwall Docks have been maintained in order that large ships can still enter these systems. Indeed construction materials and spoil for the construction of the huge Canary Wharf development has been via the docks system in the West India Docks.

The King George V Lock in the Royal Docks has an overall length of 300 metres and can handle vessels 244 metres long by 30 metres beam, with a draught of 14 metres on mean high water springs.

This wide range of new activity in the docks called for a review of the use of management of the water space in the UDA. Prompted by this, and a few early problems in maintaining an acceptable level of water quality in some areas, the Corporation initiated a Water Quality Study.

In 1987 two algal blooms occurred in the Royal Docks, first of brown algae in late May - early June and then of blue green algae in July.

These algae caused skin irritations and it became necessary to cancel some water contact activities in the docks during these periods of blooms. They also raised the issue locally of long-term water quality in the docks.

The Estates Department of the Corporation had been undertaking quarterly sampling in the docks system to check the water against microbiological and chemical/physiochemical parameters laid down in the European Commission (EC) Bathing Water Directive. Although this work gave some indication of the state of the water, it was too limited to allow the Corporation to take a pro-active role in predicting and controlling changes in the water quality.

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The LDDC implemented a study to assess the existing water quality and provide long term treatment and management strategies to ensure certain minimum standards were maintained. The study would also identify and evaluate emergency treatment systems which may prevent the sudden deterioration of water quality within a dock system. The brief included an option to evaluate the effect of water quality on developer's proposals to alter the geometry and depths of docks or to alter their water movement regimes. The principal objectives were to provide:-

• Water of the quality acceptable for use in water contact recreational activities.
• Water which is aesthetically pleasing at all times.
• Water which is free from noticeable odour, visible algal scum and contaminants.

The scope of the study was:

• Identification of relevant legislation and standards and an assessment of the water quality targets which should be achieved, bearing in mind the end use of each particular dock system.
• Identification and assessment of inputs and outputs from each dock system.
• Assessment, evaluation and monitoring of water quality and water movement within each dock system, both currently and on a regular basis in the future.
• Identification and evaluation of emergency treatment options for each dock system with recommendations for early warning, monitoring and implementation.
• Development of a long term treatment and management strategy.

A review of th