Artesian Pressure Relief for Trident Drydock

Abstract

Construction of the Trident drydock required lowering piezometric levels in a sand and gravel aquifer underlying the drydock site 100 ft (30.5 m). The design of the construction dewatering system was based on a 15‐day, 1,900 gpm (120 L/s) pump test. The dewatering system consisted of five pumped wells installed at the shore, 12 pumped wells installed through the cofferdam at the drydock site, and 15 unpumped wells installed inside the cofferdam after unwatering and subgrade preparation. Details of the well systems, installation procedures, power supplies, design features, and as‐constructed geometries, are provided. The results of individual and well system tests are presented and related to design assumptions. Construction performance of the various well systems is described. Well performance data indicated aquifer conditions were more variable than assumed for design. However, the well system as designed was sufficiently redundant to readily provide the required reduction in piezometric level to allow drydock construction.