Experimental Study Of Liquefaction Characteristics Of Gravelly Soil

The saturated gravelly sand sample will have an increasing pore water pressure and decreasing shear strength, with a phenomenon of shear contraction or dilatancy in poor drainage or undrainage conditions, when subjected to cyclic loading. The undrained shear strength should be taken into consideration in the aspect that the saturated gravelly sand’s withstanding short term cyclic loadings such as earthquakes under the same conditions, which need to be studied being associated with liquefaction problems. The generally research method is the consolidated undrained cyclic triaxial test.The previous research on the problem of liquefaction is mainly based on the saturated soil of sand or silt. It is generally accepted that the gravelly sand has a larger permeability coefficient and is not easy to be liquefied for the growth of pore water pressure being smothered and pore water easy to discharge when having a smooth drainage. That is, it is tend to be overlooked. China is in an earthquake-prone area and the gravelly soils are widely distributed and have great utilization in many fields all through the country. The circumstances of saturated gravelly soils’ liquefaction are not uncommon when withstanding earthquake forces. For instance, there are extensive gravelly soils liquefaction in the sandygravel dam shell of Shimen Reservoir in Haicheng earthquake of 1975, the sandygravel protective layer of main dam near the Miyun Reservoir in Tangshan earthquake of 1976. It has been fully vindicated that the study of liquefaction characteristics of gravelly soils is quite necessary and pressing.The studies of gravelly soils liquefaction should be improved by far. There should have a comprehensive research on it, providing reliable basis for the judgements of liquefaction potential, the analysis of liquefaction harmfulness, the basic approaches of stability enhancing, and then decreasing the seismic damage and the loss of life and property. The study is on the dynamic strength characteristics, the dynamic pore water pressure characteristics and the dynamic deformation characteristics of saturated gravelly soils from Houziyan Hydroelectric station of Sichuan province by using GDS dynamic triaxial test apparatus. The main research achievements are as follows:1. This paper describes literature progress reviews on dynamic strength of gravelly soils, and summarizes the effect laws of gravel content on the dynamic strength characteristics. And it has been concluded that the effect laws of confining pressures, confining stress ratios, relative densities and vibration frequencies on the dynamic strength characteristics of saturated gravelly soil.2. This paper also describes literature progress reviews on dynamic pore water pressure characteristics, and analyses the dynamic pore water pressure characteristics of gravelly soils liquefaction tests. It compares pore water pressure-stress model and pore water pressure increment model put forward previously with the experiment results, and combines the application to calculating the reference values. The relational expressions between dynamic pore water pressure ratio and shearing strain ratio have been presented in this paper by drawing on the experience of pore water pressure-stress model, involving the gravel content parameter and vibration frequency parameter, and the one with static shear strength parameter. The experimental parameters values have been given at the end of the expression.3. In addition, this paper describes the dynamic modulus of elasticity and damping ratio of domestic and foreign literatures. And it summarizes the effect laws of gravel content on dynamic stress-dynamic strain backbone curves, dynamic modulus of elasticity and damping ratio.