New Progress in Experimental Study of Deep Overburden Characteristics

Abstract

In recent years, with the further development of water conservancy and hydro-power engineering in our country, more and more water conservancy projects have to be built on the overburden. Great progress has been made in exploration, testing, seepage prevention and deformation calculation of deep overburden at home and abroad. Among them, the exploration and test of deep cover layer of dam foundation is the most basic and main technical problem of using deep cover layer to build dam. The soil test is a direct and effective means to find out the physical and mechanical characteristics of deep overburden, which provides important design and calculation parameters for rational utilization and engineering treatment of deep overburden in river bed. However, the current engineering experience of dam construction on overburden is mostly limited to shallow overburden. With the increase of overburden thickness, how to accurately obtain basic indexes such as natural density, water content and grading have become the focus, difficulty and key point of deep overburden test. The sand layer, clay layer, egg (block) and gravel (broken) layer in the shallow part of the overburden layer can be excavated to obtain the original sample, and then obtain the corresponding basic physical parameters. However, in the survey and design stage, due to the restrictions of survey means and conditions, the basic physical parameters of deep soil can not be obtained by large excavation. Sand layer and clay layer are sampled by conventional drilling, and the density may change. The egg and gravel layers are sampled by conventional drilling, the layers are unchanged, the composition and structure change, and the density is difficult to obtain. This paper introduces the new development of sampling methods for large bore holes, simultaneously, the representative drift-gravel layer of Shuangjiangkou hydropower station is selected, and the relation curve between the laboratory side pressure test modulus and soil layer density is obtained through model test.