Quality for long-term Use: Hangers support Victorian Sewer Pipe System
Even today, the sewage system in London still largely consists of the canal system that was conceived by the engineer Bazalgette in the 1860s in order to free the city from what was known as “the great stink”. Simultaneously, the new sewage system eliminated the cholera epidemic raging at the time.
As Bazalgette had chosen to build the sewer pipes more than twice as large as necessary, the Victorian System continues to transport the wastewater of a population of 8 million that is now more than three times as large as it was at the time the system was built.
The historic sewer network consisted of 1,800km of street sewers that flowed into 132km long main sewers. The main sewers, which are still intact today, have diameters of up to 3.2m and run parallel, with up to 7 canals running side by side.
In the east of London, the sewer pipes cross the inland waterways River Lee and Channel Sea in what is known as the Northern Outfall Sewer. Here, the sewer pipes are integrated into Victorian steel and cast iron bridges spanning the tributaries. The canal pipes are suspended from the bridge girders by tie rods that were badly corroded and had to be replaced. In conjunction with the design engineer, DSI Construction Great Britain developed a solution to replace the existing tie rods by hangers consisting of GEWI® Steel.
The 150 28mm Ø GEWI® Hangers were supplied in two sections; one of the sections had a crank, a coupler and a load bearing hex nut installed in order to anchor the bar at the girder flange at the top.
Additional supporting anchorage points were arranged at mid flange, and at the lower end, termination points served to stabilize the underside cradle.
In addition to the fully threaded coarse thread, the advantage of the GEWI® System was that the threadbars could be bent in the lower bar section. While the old ties were being replaced by the new GEWI® Tie Rods, DSI stabilized the sewer pipes using temporary tendons. These tendons were equipped with load cells to monitor the load in the sewer barrels.
DSI also developed a precise loading sequence to ensure progressive load transfer between the old and the new tie rods. The temporary tie rods resting on the top girder had different vertical inclinations. Consequently, special rocker plates were required to place the load cells in line on each tendon.