Experimental Study On Sand Layer Liquefaction Mechanism Under Loess Landslide Impact

Most of the Loess Landslides in the Southern Plateau of Jingyang are high-speed and long-distance landslides.They usually start quickly,slide far away,have strong destructiven,ess and wide disaster-causing scope,which bring great potential safety hazards to the local residents'production and life,and seriously restrict the economic development of the region.Soil liquefaction is one of the important movement mechanisms of high-speed and long-distance landslides.Based on the study of the movement mechanism of loess landslides under impact liquefaction of the National Natural Science Foundation of China,taking Ximiaodian landslide in Jingyang County as an example,physical and mechanical parameters of soil samples were obtained through field investigation,data collection and collation,and routine indoor experiments.On this basis,impact test equipment and test were designed.The impact simulation test was carried out.Three groups of 11 tests were carried out to monitor the changes of soil pressure and pore water pressure under the variations of void ratio,saturation and drop distance.The relationship between soil pressure and pore water pressure with time was analyzed,and the mechanism of impact liquefaction was analyzed.The main research results are as follows:(1)The liquefaction behavior of sand layer is affected by its saturation.When the saturation of sand layer increases,the liquefaction of sand layer is more likely to occur under impact.However,the saturation of terrace sands in the Southern Plateau of Jingyang is affected by the groundwater level.A large number of farmland irrigation increases the groundwater level in this area,which makes the saturation of terrace sands rise,and the sands of terrace sands are liable to liquefaction when the sliding body impacts on the terrace sands in the course of landslide movement.(2)The liquefaction behavior of sand layer is affected by its void ratio.When the void ratio of sand layer increases,the liquefaction degree of sand layer under impact is higher.(3)The drop distance of impact hammer is related to the liquefaction behavior of sand samples.The larger the drop distance,the higher the liquefaction degree of sand samples.The larger the relative drop between landslide slides and terrace saturated sand layers(i.e.the greater the impact energy),the higher the liquefaction degree of sand layers,the greater the pore water pressure,and the faster the dissipation.(4)Impact liquefaction mechanism.When the sliding body impacts the saturated sand layer on terrace,the volume of sand layer is compressed dramatically in a very short time,and pore water can not be discharged in time.The stress part(or all)borne by soil particles before is changed to borne by pore water,resulting in rapid increase of pore water pressure,rapid decrease of effective stress,and different degrees of liquefaction of sand layer.