TerraFirma Earth Technologies was contracted by Zachry Corporation to perform the dewatering of the Bayport Terminal 3 complex.
The project consisted of the construction of a new terminal for the loading and offloading of containers from cargo ships in the Houston Ship Channel. The area to be dewatered was approximately 2100’ long, by 200’ wide. Approximately 50’ from the Ship Channel, the structure was supported by sheet piling on the channel side, with an open cut excavation extending to El (-56).
A combination of deepwell dewatering wells installed within over-sized bore holes, and intermittent sand wicks/drain pipes installed along the site perimeter, were proposed as a means of temporarily “depressurizing” the proposed excavation. The primary function of the deepwells was to relieve excess hydrostatic pressures in the pervious and semi-pervious foundation soils below El (-) 47.0 msl, to a point where the mass excavation could safely begin. The primary function of the sand wicks/ drain pipes was to minimize, as much as practical, horizontal seepage emanating from the semi-pervious stratum(s) located within the highly variable, predominantly clay strata above El (–) 47 msl. The deepwell dewatering wells consisted of 6” and 8” PVC well materials placed within an oversized, 30” diameter bore hole, fully penetrating the pervious and semi-pervious foundation layers between El (-) 47.0 and (-) 70 msl. Electrically driven submersible pump/motor assemblies were placed near the bottom of each well. Discharge water from each well was directed via a common discharge header system (HDPE) surrounding the site, to the adjacent ship channel. Sand wicks/drain pipes fully penetrated the same subsurface formations, allowing the upper waters from the less pervious predominantly clay soils, to drain to the relatively more pervious “depressurized” lower sands. Additionally, to assist in the “capture” of any perched/trapped water within the upper predominantly clay soils, the deepwell dewatering well well-screen, was brought up to within 15 feet of the current ground surface (the approximate current ground water table).