Geotechnical site characterization for reservoir sediment

Abstract

The unusually strong typhoons and heavy rainfalls occurred recently in Taiwan have caused major landslides in many reservoir catch basins. The debris from these landslides eventually settled in the reservoir and turned into mud. From soil mechanics point of view, the mud in front of the dam is a very young, normally consolidated or under-consolidated soil. The engineering properties of the reservoir mud are important design parameters in the planning and design of schemes to remove the mud. Yet, our knowledge in this regard is very limited. For the major reservoirs in Taiwan, the mud is often under more than 40 m of water. How to conduct effective geotechnical site characterization under these circumstances is a challenge. The authors developed a differential pressure flat dilatometer (Delta DMT) and a piezo-penetrometer (Delta Pu) to facilitate in situ tests under water in a reservoir. A series of field Delta DMT and Delta Pu tests along with representative soil sampling were conducted at Tsengwen Reservoir in Southern Taiwan. The paper describes the techniques of differential pressure DMT and piezo-penetrometer tests, interpretation of available test data to obtain the engineering properties of the reservoir mud, and discusses implications in future site characterization of reservoir mud.