Dewatering the Port Allen Lock Excavation

Thirty-six large-diameter deep wells were installed around the top of the excavation for Port Allen Lock for the purpose of lowering the hydrostatic head in the deep stratum of pervious sand that lies beneath the lock. Specifications for the project required that the number, arrangement, and capacity of the wells and pumps be capable of reducing the hydrostatic head in the deep sands to a level 5 ft below the bottom of the excavation (about el -26 mlg) with a river stage of 45 ft mean low gulf (mlg). It was required that the ground water table in the excavation areas and behind the excavation slopes be lowered as was needed for satisfactory construction operations. After completion of the excavation to within 5 ft of grade, the water table in the foundation was to be maintained 5 ft or more below the bottom of the excavation until construction work would permit flooding the structure. Approval of the dewatering system was contingent, in part, on its proven performance. After installation of the deep well system, tests were made to determine its adequacy.