Numerical Analysis Of High Slope Stability Of Composite Support Cutting Under Earthquake And Rainfall

The construction of mountain railway has become a necessary development trend to promote the economic development of many regions in China.As a common composite support structure,frame anchor structure-anti slide pile can improve the stability of high cutting slope.As the two main factors inducing landslide,rainfall and earthquake are essential to study the instability form of high cutting slope strengthened by composite support structure under rainfall,earthquake and their combined action,the stress characteristics and anchoring mechanism of support structure,but there is a lack of research in this field at present.Therefore,taking the section of a high cutting slope of Xingquan railway line as the research object,this paper analyzed the dynamic response law and seepage characteristics of the slope and support structure of the high cutting slope with composite support under EL wave earthquake and rainfall-EL wave earthquake by using the methods of model test,numerical calculation and theoretical calculation,and evaluated the dynamic stability of the composite support slope by using the FLAC3 D complete dynamic analysis method and the upper bound method of limit analysis.The main research results are as follows.1.According to the soil layer parameters obtained from the indoor test and the self-made earthquake and rainfall program,the numerical calculation under the same working conditions as the indoor shaking table model test was carried out.The calculation results are basically consistent with the variation trend of the measured data.It shows that the saturated unsaturated seepage calculation program of slope rainfall infiltration developed by FISH language based on FLAC 3D can be well applied in engineering example to verify the effectiveness of the numerical calculation program.2.Under the two working conditions,the PGA amplification factor of measuring points on the slope surface is significantly higher than that in the slope.Due to the existence of step platform on the slope surface,the PGA amplification factor at the top of each grade of slope increases sharply.PGA amplification factor has obvious elevation effect and surface effect,and decreases with the increase of seismic peak acceleration.The PGA amplification factor of slope under rainfall-earthquake is smaller than that under earthquake,indicating that the shallow local soil has a certain damping effect after rainfall.The displacement produced by the combined action of earthquake and rainfall is much larger than the sum of the displacement produced by the two alone.3.Under the two working conditions,because the slope frame anchor structure is not anchored to the sliding surface,the frame anchor structure not only bears the pressure exerted by the sliding of the soil in the middle and upper part of the slope,but also bears the thrust exerted on the frame anchor structure when the sliding body slides outward.The actual tension or compression of the slope frame anchor structure depends on the size of both.The fifth grade slope frame anchor structure bears the maximum force,and the safety reserve shall be increased at the anchor head position of the anchor bolt.The earth pressure and sliding thrust of frame anchor structure on the slope under rainfall-earthquake will be greater than that under earthquake,mainly showing that the seismic intensity is greater than 0.4g,the failure of anchor cable frame beam and the maximum prestress loss of anchor cable increased to 78.5%.The peak value of dynamic bending moment and post earthquake bending moment of anti slide pile under rainfall-earthquake are larger than that under the earthquake before 0.3g,but smaller at no less than 0.3g.The reason is that when the earthquake intensity is high,the combined action of the two adverse factors leads to the weakening of the plane soil arching effect on the top of the pile,the reduction of the load sharing ratio of the plane pile on the top of the pile,the increase of the displacement of the soil between the piles,the decrease of the displacement of the pile top,the decrease of the bending moment of the pile body,and the increase of the spalling displacement of the soil between the piles will also reduce some of the earth pressure on the pile body.4.Based on the FLAC3 D complete dynamic analysis method,the static and dynamic safety factors under two working conditions were calculated.The results show that under the two working conditions,the safety factor of composite support slope decreases first steeply and then approximately linearly with the increase of seismic peak acceleration.The safety factor is lower under the combined action of rainfall and earthquake,and the difference of safety factor increases with the increase of peak acceleration.It shows that the joint action of rainfall and earthquake does great harm to the slope.5.The static and dynamic safety factors of the slope studied in this paper were calculated based on the limit analysis upper bound method of anti slide pile reinforced slope with or without weak interlayer in the combined failure mode of rotation and translation.The results were compared and evaluated with the calculation results of limit equilibrium method and complete dynamic analysis method.The results show that the variation law of safety factor with earthquake magnitude is consistent.The difference of safety factors between rainfall earthquake and earthquake calculated by limit analysis upper bound method have nothing to do with magnitude,while the difference between them increase with the increase of magnitude under complete dynamic analysis method.