One of the greatest feats of highway engineering that London has ever seen was the building of Silvertown Way, a mile-long stretch of elevated highway which carries heavy traffic for the docks over minor roads, railways and other obstructions.
SILVERTOWN WAY was opened in September 1934 to relieve the extreme congestion on the streets which gave access to the Royal Docks in the Port of London. The new road has a total width of 108 feet, and at the point here shown it divides into three ways, the centre one rising to form a through-traffic viaduct 25 feet above the side ways, which serve local traffic requirements.
IN the Port of London three large docks, the Royal Victoria Dock, Royal Albert Dock and King George V Dock, comprising a water area of 245 acres, are part of one of the most important dock systems in the world. Trade handled at these docks is now carried in swift lorries along a gleaming new road known as Silvertown Way, which was opened to traffic in September 1934.
The designers of the road were faced with a tangled huddle of mean houses and streets, with narrow twisting roads hampered by a swing bridge, by level crossings and by right-angled turns. Their task was to transform this pitifully inadequate approach to the docks, long a disgrace to London, into a straight, wide avenue along which heavy lorries could travel without danger or halt. To-day a mile-long white ribbon, transformed into a T by two broad approach roads at the top, cuts straight down from East India Dock Road and Barking Road into the heart of the Royal Docks. Most of this magnificent new avenue is raised high above the small streets in a broad viaduct which skirts the adjacent chimney-tops.
The congestion on the main approach to the Royal Docks was appalling as long ago as 1902, when the first protests were made by Silvertown factory owners and traders. By 1924 the approach along Victoria Dock Road was daily in a state of chaos. This road, which had to carry almost the entire lorry-borne trade of the world's busiest docks, was only 21 feet wide in many parts. It was crossed by numerous side streets; it was entered by an awkward right-angled turn; and it was obstructed by playing children. Worse still, it was crossed by two railways at street level and had to traverse a narrow swing bridge. Experts estimated that this important stream of traffic was completely blocked to progress for nine out of the twenty-four hours. The first level crossing was often closed to traffic for forty-six minutes in the hour.
Farther down the road was a swing bridge over the water entrance to the Royal Victoria Dock. This bridge was often open, totally blocking road traffic. Even when it was closed affairs were only slightly better, for the bridge was so narrow that it could take one-way traffic only. Moreover, it had to carry a railway track as well as road traffic. Farther still down the approach road was yet another level crossing. Thus traffic spent at least 35 per cent of its journey from the docks at a standstill.
It can be seen therefore why the estimated expense of £2,500,000 which would be incurred in building proper approaches to the docks drew no protests from anyone. Local authorities gladly granted £630,000 of this sum and the rest was taken from the Road Fund.
NEW ROAD WORKS in the vicinity of the Royal Docks. Silvertown Way runs from East India Dock Road and Barking Road to join North Woolwich Road in Silvertown. Another viaduct diverts through traffic to avoid the level crossing near Silvertown Station.
The plan called for a mile-long road - Silvertown Way - running straight from Barking Road, near Canning Town Station, past the Royal Victoria Dock to North Woolwich Road. This was to be served by two approach roads - already existing but needing entire reconstruction - crossing the T.
Before any work could start, a great new rehousing scheme was planned. To drive the new road and viaduct through such a congested area involved the demolition of 500 houses and the displacement of 3,600 people. These people had first to be rehoused nearby in a new “village” of 600 houses - all with gardens - and flats. It sprang up and was finished in August 1931.
The next work was the building of a broad new bridge over the River Lea to replace the awkward, right-angled narrow Barking Road Bridge. Previously traffic going from East India Dock Road to Barking Road and the Royal Docks approaches had to swing sharp right, cross this narrow bridge and swing sharp left again. The new bridge sweeps straight on and connects the two roads without turns.
There were many problems here. The first was the nature of the ground. Beneath existing roadways the ground was composed of mud, peat and other soft materials that would readily give under loads of more than 4 cwt. to the square foot. The new road had to be designed to carry large loads, much greater than those of existing motor lorries. When the designs were prepared
those responsible foresaw great goods “trains”, composed of giant four-wheeled lorries weighing up to 100 tons, drawn by three 20-tons “engines”. All the specifications were drawn up to provide the extraordinary strength which such “trains” would demand.
Single 200-feet Arch
On the way to the docks from the City or West End, the first section of the new road to be met is the western approach, which leads up from East India Dock Road to the new bridge. This new stretch is 1,000 feet long, surfaced with heavy, almost everlasting granite setts and has a maximum gradient of 1 in 40. Large numbers of 14-in.-square piles up to 50 feet long were driven through the comparatively soft subsoil into the firm clay beneath, to support the road, which climbs to bridge level on ten reinforced concrete arches. The regrading of this road involved considerable alteration to side streets and adjoining property, and the replacement of a number of public service mains.
On the other side of the bridge the eastern, or Barking Road approach, was one of the most complicated sections of this part of the work. This section had to be regraded, an operation which meant modifying side streets and demolishing property. The roadway in front of Canning Town Station had to be raised about five feet, so that station buildings fronting on the road had to be demolished and rebuilt and a girder bridge over the railway also had to be reconstructed. By completing this work in four stages there was little interference with the busy traffic. In one section of this approach road the unstable ground made exceptional foundation work necessary. The new road level here was up to 11 feet above the original level, and as considerable settlement of this filled-up section would be certain to occur under heavy loads - with a possible fracture of the surface - hundreds of heavy piles were driven into the earth along the route. When the ground.had been prepared with piles the remaining space was filled with poured concrete, which set in a homogeneous and immensely strong mass.
The building of the new Barking Road Bridge was fairly simple, but first the banks of the River Lea (or Lee) had to be disciplined to a new alinement. This was done by driving a “fence” of 18-in by 16-in piles along the banks, anchoring them with concrete ties to anchor piles and covering the intervening bank with a 6-in concrete sheeting.
The bridge itself has a single 200-feet arch supported on two massive abutments. These abutments were supported on 460 14-in-square concrete piles driven deep down into the firm blue clay.
As a clear waterway 100 feet wide had to be kept open for river traffic, no staging could be used for the central part of the span. From either bank, therefore, the steel ribs of the bridge were cantilevered out over the river, with their outer ends slightly above the final positions they would take. When this stage had been completed, both halves were lowered simultaneously until they interlocked, forming one continuous structure.
With the building of the eastern and western approaches, the Barking Road Bridge and the widening of one or two side streets, the head of the T was completed. While this work was proceeding, hundreds of men were engaged in clearing the site of the main stretch of the scheme - Silvertown Way. Houses and streets were levelled, leaving an open line, in places 140 feet wide, running straight down towards the Royal Docks.
The beginning of this long, straight avenue is in Barking Road, east of the new Barking Road Bridge. The first section, which is known as Burnham Street, has a total width of 80 feet and runs at ordinary street level for some 300 yards. It is here that Silvertown Way really begins. The whole roadway widens out to a breadth of 108 feet and at the same time splits into three. The centre section rises to form the viaduct, the two side sections continuing on either side as low-level roads to serve the surrounding streets.
The viaduct rises gradually to a height of about 25 feet above the lower roads, so that its surface is on a level with the roofs of the surrounding houses. For three quarters of a mile it runs without a single crossing or interruption, being connected to the Royal Victoria Dock by spur roads, which slope off at oblique angles. Along this magnificent raised highway heavy lorries can maintain a steady thirty miles an hour. In contrast to the 21-feet width of Victoria Dock Road, Silvertown Way measures 40 feet between kerbs, enough for four lanes of traffic. In addition it has two footpaths of 10 feet each.
The lower roads carry a great volume of slower local traffic, which is thus prevented from slowing down express “through” trans-port to the main docks.
With majestic indifference Silvertown Way skims over crossroads, railways and dock entrances, taking in its stride all the obstacles which formerly delayed the great stream of traffic. In all it includes eight reinforced concrete bridges - five over crossroads, one over a passage way, one over the Port of London Authority Railway crossing and a 103-feet span over the entrance channel of the Tidal Basin. Silvertown Way finally slopes down again and reaches ground level to connect with North Woolwich Road.
Parapets of Great Strength
To support the immense weight of the roadway and that of the traffic which passes overhead, forests of piles had to be sunk. These numbered 3,500 and had a diameter of 17-in. Their average length is 38 feet and most of them were cast in their final position in the ground. The columns and beams of the viaduct rest not on single piles, which would not have been strong enough to support the weight, but on “pile caps” which cover clusters of two, three or four piles, according to the load.
The whole construction is of concrete, heavily reinforced with steel rods up to 1½-in thick. These rods were fixed in place and interconnected before the concrete was poured, so that the two elements form an immensely strong partnership. A standard form of construction was used. The roadway is carried on a concrete deck 1 foot thick, resting on transverse and longitudinal beams, which are themselves supported on rows of six columns rising from pile caps. A standard section of roadway is 55 feet long, and is separated from its neighbours by expansion gaps. Granite sett surfacing is laid above the concrete, to resist the ceaseless pounding of heavy lorries. The parapets had to be of great strength to prevent the possible danger of vehicles crashing through and down into the streets below. They are of heavily reinforced concrete faced with artificial stone.
One of the most complex jobs in the viaduct was the building of the three-span steel bridge which carries it over two roads and a railway. This point, about halfway down the Way, used to be one of the worst congestion spots of all. Here the tracks of the L.N.E.R. swing east to enter the Royal Victoria Dock; here, too, Victoria Dock Road branches east, and a few yards farther the short Tidal Basin Road moves parallel with it. But the long swift viaduct sweeps calmly overhead.
The three spans of this bridge are of different lengths and total about 207 feet. The two intermediate supports are provided by rows of cruciform steel columns, with their recesses filled with concrete. It was no easy task to secure these supports without interference to the already overcrowded roads and tracks below.
DRIVING A NEW HIGHWAY through the heart of dockland. The Silvertown Way project involved the demolition of 500 houses, and new homes had to be built for 3,600 people. The western approach to the bridge over the River Lea involved considerable alteration to adjoining streets and property- The road climbs to bridge level on ten reinforced concrete arches.
The 103-feet concrete bridge over the Tidal Basin entrance was simpler to build. The foundations were built in steel cofferdams sunk into the solid clay. The tops of the cofferdams were later cut off at the level of the surface, leaving their lower sections firmly embedded. Work was postponed a short time here when one of the cofferdams collapsed while foundation excavations were going on, but by driving a larger cofferdam round the damaged one it was possible to excavate the site without much delay.
After having crossed the Tidal Basin, the elevated highway continues alongside North Woolwich Road - which formerly used to carry the whole stream of traffic - for about a hundred yards, eventually sloping down to merge with it. At this point the traffic is not so intense, as it has been served by two spur roads down to the docks which have relieved it of much of its burden. North Woolwich Road can therefore deal with the remaining flow.
Farther east are more obstacles. Yet another level crossing blocked the stream of traffic in North Woolwich Road at Silvertown Station. So a separate scheme was drawn up for another, though shorter viaduct which would lead traffic by a direct loop from North Woolwich Road, over several streets and the railway lines on a wide bridge and down again on the other side of the obstructions.
The viaduct, which is about one third of a mile long, is similar in construction to the great viaduct on Silvertown Way and, but for the inevitable comparison, would itself have ranked as a great constructional feat.
As traffic is not so dense in this section, the roadway is only 28 feet wide, narrowing to 20 feet on the spur road which leads down from the high level viaduct to the docks. The main feature is a “bow-string” girder bridge with a clear span of 109 feet which carries the roadway over the railway and Connaught Road. Here again the softness of the subsoil and the huge weights to be borne made heavy concrete piles necessary. About 900 were used on the diversion.
Stringent tests were applied to the concrete used in building the viaducts. In places where specially high stresses were likely, specifications insisted that the concrete should be consolidated as much as possible by mechanical vibrating. No special apparatus was used, but light pneumatic riveting hammers applied to the outside of the forms had the desired result—the densest concrete that could be made.
MASSIVE ABUTMENTS for the Barking Road Bridge across the River Lea were supported on 460 concrete piles. The steel ribs of the 200-feet arch were cantilevered out from either bank. When completed the two halves were lowered until they interlocked.
Contracts stipulated that all concrete used should withstand heavy crushing forces. Specimen 6-in. cubes of concrete were made on the spot, taken to a special laboratory, and tested by a crushing machine able to exert a force of 150 tons. About 3,000 test cubes were examined and in most instances the strength was well above the minimum required. Tests with one type of concrete, which should have had a crushing strength of 4,800 lb. per sq. in., showed an average resistance of over 7,700 lb. It was tests such as these that ensured that no weak materials should endanger the great scheme.
Silvertown Way is finished. But the work of improving the approaches to the world’s greatest docks still goes on. Another vast scheme involves the building of new roads and viaducts, the widening of old roads and the re building or elimination of ten awkward bridges.
Stringent tests were applied to the concrete used in building the viaducts. In places where specially high stresses were likely, specifications insisted that the concrete should be consolidated as much as possible by mechanical vibrating. No special apparatus was used, but light pneumatic riveting hammers applied to the outside of the forms had the desired result—the densest concrete that could be made.