ROCK DREDGING ON THE MALABAR COAST OF INDIA

The Dabhol Power Project in 1997 was the largest foreign investment project in India. The Project was planned to have over 2000 Megawatts of power generation, an LNG terminal, and an all weather harbor to receive fuel deliveries. The site was located on the exposed Malabar Coast of India nominally 160 kilometers south of Mumbai. The green-field development included an eight kilometer dredged channel and turning basin, a 1750 meter long unloading pier, and 2300 meters of rubble mound breakwater to protect the channel, turning basin, and berth. The entrance channel to the port was very nearly parallel to the existing offshore contours and extends for approximately 8 km to the 14-meter depth. Total dredging in the channel amounted to about 8,700,000 m 3 . Offshore disposal of the material occurred near the 20-meter contour. Because of the monsoon, construction operations were limited to 8 months annually. For a variety of reasons, geotechnical investigations prior to construction were severely limited. Planners attempted to locate the channel and turning basin to avoid rocky areas near the site. Unfortunately, once construction began a significant amount of rock was discovered in the dredge templates. Because of concerns in the local fishing communities, the contractor used non-explosive methods to remove what, in some cases, was extremely hard rock. The process consisted of removal of very soft overburden by a conventional trailing suction hopper dredge. A large hydraulic chisel then mechanically pretreated the hard material. Finally a bucket ladder dredge removed over 300,000 m 3 of rock. The site also faced a significant challenge in terms of sedimentation. The southwest monsoon results in severe wave and current conditions at the site, particularly during July and August. These conditions fluidize silty material, which flows readily on the bottom into any low areas in the seabed. This created siltation during the construction period. A variety of innovative methods were used to minimize the impact of these issues on the project.