Study On Stability Of Expansive Soil Landslide In Southern Shaanxi Under Earthquake

Expansive soil is widely distributed in the mountainous area of southern Shaanxi.When it meets with water,it expands and its strength decreases.It shrinks with water loss and produces cracks.Therefore,landslide will be induced under extreme conditions and loss will be caused.it is very important to study the slope landslide of expansive soil.In this paper,the landslide stability of expansive soil is studied by means of geotechnical test and numerical simulation.(1)The remolded expansive soil,which is the same as that in the mountainous area of southern Shaanxi,was prepared,and the geotechnical tests of expansive soil were carried out in the laboratory.The deformation parameters of expansive soil under different confining pressures,including volume modulus and Young’s modulus,were obtained through triaxial compression tests.The tensile strength was measured by splitting test.The shear modulus,Poisson’s ratio and shear strength of expansive soil are obtained by calculation.The volume modulus,Young’s modulus and shear modulus increase with the increase of confining pressure,while the Poisson’s ratio and tensile strength do not change significantly.(2)With reference to the landslide case of Chenjiaying Village,the FLAC3D simulation software was used to establish a slope model with a slope of 15 degrees.According to the laboratory test parameters,the soil partition was assigned values and the static calculation was carried out to study the stability of the landslide under the static force.In addition,the cracks were arranged according to the mechanical characteristics to study the influence of cracks on the stability of the landslide.The results show that under static conditions,the shear stress at the toe of slope is the largest,and there are hidden dangers of shear failure and soil sliding.The existence of the crack reduces the surface tension of the slope and transfers it to the bottom of the crack,which concentrates and increases the tension.The existence of cracks causes the shear stress at the toe of slope to increase and the safety factor of slope stability to decrease.The pressure around the crack is very small and even produces tension,which reduces the shear resistance of the crack.Therefore,compared with the non-crack slope,the fractured slope is more prone to instability failure and landslide disaster.(3)The FLAC3D software was used to analyze the landslide stability under dynamic action.The landslide stability was analyzed qualitatively and quantitatively mainly through the dynamic response of the slope body,and then sine waves were applied to the slope body to study the influence of pore water pressure on the dynamic results.The results show that compared with other parameters,the horizontal force has the greatest influence on the normal stress of the soil element in this direction,and the height of the element and the stress in the static state also affect the normal stress.Under the effect of octave earthquake,the existence of cracks increases the soil normal stress by about 22.1%,and has little effect on the shear stress.With the increase of normal stress,the shear strength of the slope decreases.If the seismic intensity is too large,the normal stress exceeds the ultimate tensile strength of the soil,the collapse failure will occur.The pore water pressure has an adverse effect on the stability of slope body,which increases the soil stress and increases the risk of landslide.(4)The dynamic response and dynamic time history stability safety factor are calculated by using Midas GTS NX finite element software,according to the landslide modeling of chenjiaying village,and some results calculated by FLAC3D are compared and analyzed to study the landslide stability.The results show that the deformation of MIDAS GTS NX is larger than that of FLAC3D under static conditions,but the slope stability is good,and the safety stability coefficient is 9.4%lower than that of FLAC3D.Seismic wave reduces the safety factor of stability of 15-degree slope by 21%.In the time of earthquake action,two kinds of failure modes of sliding landslide or traction landslide may occur in the slope at a certain time.