SGH designed support for a 150 ft wide by 300 ft long and 35 ft deep excavation to accommodate underground detention basins that can hold about 2.2 million gallons of combined sewage. The earth support system consisted of steel sheet piling and two levels of steel bracing. The struts spanned significant distances and for intermediate vertical support, we designed two lines of pin piles with built-in adjustment to maintain strut alignment due to base heave.
SGH performed a staged analysis to determine bracing loads and wall deflections. We required all bracing to be preloaded with hydraulic jacks to minimize wall deflections and adjacent earth movements. We coordinated the earth support design with final construction details and helped develop detailed phasing plans and construction sequences to outline the contractor’s means and methods.
At the pump station, SGH designed a bulkhead/cutoff wall that consisted of steel soldier piles and wales with timber lagging filled with a cement-bentonite mixture. The bulkhead wall enabled Barletta to demolish and reconstruct a significant portion of the wet well and discharge chamber while maintaining operation of the MWRA pump station and maintaining a watertight bulkhead. During construction, SGH oversaw a series of trial batches and performed laboratory testing to confirm appropriate field mixing of the bentonite in the concrete delivery trucks.