The Thames Tideway Tunnel, an ongoing project in West London, has called for some innovative excavating solutions. About 15.5 miles long, the tunnel running under the river Thames will be handling and diverting the sewage and rainwater from the river.
One issue to tackle was reducing the water pollution from the raw sewage released by Lots Road Pumping Station—"enough to fill 400 Olympic swimming pools," according to Greg Pitcher at newcivilengineer.com. The contractors excavated a 98-foot shaft that extended down to the new tunnel, which reduced the water pollution by over 90%.
Another excavation was needed to store the air treatment equipment that would stop contaminating sewage gases from coming up to the surface. Pitcher writes, "It had to fit into a very tight space between the main shaft and the foundations of the 116-year-old Grade II listed pumping station itself, posing a major civil engineering challenge." The team had to focus on both worker safety and maintaining the integrity of the site's infrastructure.
The solution involved installing interlocking Larssen steel sheet piles to a depth of about 33 feet around the perimeter of the excavation. The workers also used two methods of excavation when constructing the shaft. Pitcher explains, "Intersecting secant piles were installed around the shaft perimeter to a depth of approximately [52.5 feet] and the area within was excavated."
