Water & Wastewater Treatment

PROJECT FOCUS A 50m duplex stainless steel lining was jacked into the existing 2.06m-diameter sewer Perspectives The client "The works will never be seen by the general public, but the challenge and innovative solution created has ensured damage mitigation – if it had failed a large portion of the sewerage for East London would have had nowhere to go. The consequences of failure would have created a catastrophic effect for East London residents and businesses." Kim West, associate director tunnelling at Arup, Crossrail Project The Contractor "The works are situated on a small urban site, further restricted by diversions being carried out by DSJV on major trunk mains, which posed a challenge in their own right, and were a consideration in everything we did on the HAM sewer from an interface and programme logistics point of view. Throughout this process DSJV and UKDN Waterflow mwwaintained a healthy relationship, dedicated to innovation and solutions, which was key to delivering our ultimate goals – asset protection, TBM passage, and most importantly an unblemished safety record." Jon Hynes, utilities agent, DSJV Crossrail Contract 305: Eastern Running Tunnels Reinforcement A temporary works design was put forward by UKDN and initial work included reinforcement of the Ham Sewer with a temporary protective metal and rubber installation support cage. This enabled the creation of two shafts, one for over-pumping of wastewater from the Ham to the adjacent Wick sewer, and the other as an access shaft within which the huge steel liners could be lowered. The temporary liners protected the sewer as massive sheet piling girders made safe the access and over-pumping shafts. DSJV sheet piled both shafts using a Giken silent piling rig. This was to avoid damage to surrounding buildings and a nearby retaining wall prior to excavation of the 10m x 6.8m x 13m deep drive shaft and the 8m x 6.8m x 16m deep over-pumping shaft. UKDN suggested over-pumping the dry weather flow (DWF) from the Ham Sewer to the Wick Sewer during the whole works. To enable this to happen, a new weir and penstock valve design blocked the flow, diverting it into the pump chamber. Here six 300mm pumps accommodated a total DWF of 2,000l/s, pumping wastewater up the 14m shaft into the adjoining Wick Sewer. In all, three generators provided 1.2MW of electricity to pump round the clock. During peak flows of up to 8,000l/s, the penstock had to be raised to permit the storm flow to pass through the work site. Upstream monitoring, traffic light evacuation procedures, and alarm warnings were established and tested many times during the works, with no single accident on site. Water mains' diversion The complex site also housed construction teams from contractor Murphy, who were simultaneously diverting mains water pipes similarly affected by the tunnel-boring works. This meant that the project working conditions were very tight. The site being squeezed between the dual-carriageway approach to the Blackwall Tunnel on one side, and housing on the other, meant that some of the manholes used for this project were located either on the carriageway or within the central reservation, making access an issue. Chris Haslam, UKDN's principal project manager, said, "We used jacking rails fixed to the floor of the sewer with over 400 bolts to guide each five metre, five tonne section into place and, with a design tolerance of only 1mm, we used precision laser guiding and modified gun-sighting lasers to ensure 3D accuracy. u 14 January 2014 Water & Wastewater Treatment 13

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