Design and performance of a 15m deep excavation for a wagon tippler

As a part of bulk handling facility at one of the major ports on the east coast of India, a 15 m deep excavation was carried out for construction of a wagon tippler and belt conveyor tunnel. RCC diaphragm wall has been provided as a temporary support for 20 m x 70 m excavation. During execution, the dewatering system provided was found to be inadequate in view of the high permeability of cohesionless strata. To meet construction schedule, direct pumping of water was adopted from the excavation which resulted in large quantity of seepage into the excavation and settlement of the diaphragm wall panels. This also resulted in considerable subsidence of the surrounding area resulting in severe distresses to a building adjacent to the diaphragm wall. This paper describes the details of the structure, strata condition, design of excavation, problems faced during execution and the remedial measures adopted.