Study On Excavation Design Of High Cutting Slope Under Rainfall And Earthquake

In recent years,with China’s vigorous development of railways,China has become the world’s largest railway country,and China is a mountainous country.When the railway passes through mountainous areas,a large number of cutting slopes will be formed.The safety and stability of slopes is particularly important for the normal operation of the railway.The first thing to be determined in cutting slope excavation is the slope angle.A suitable slope angle can not only maximize the project benefit,but also ensure the stability requirements of the slope.Therefore,selecting a suitable slope angle is particularly important in slope engineering.Xingquan railway is a national class I railway from Jiangxi to Fujian Province in China.Dehua station in the line is located in Quanzhou City,Fujian Province.There is a high cutting slope next to the station.Dehua station is located in the subtropical marine monsoon climate zone,and according to the seismic ground motion parameter zoning map of China,the seismic peak acceleration in this section is 0.05 g,characteristic period of ground motion response spectrum is 0.35 s.Therefore,the construction site is affected by heavy rainfall and earthquake.Relying on the high cutting slope construction site beside Dehua station,according to the methods of numerical simulation,theoretical calculation and comprehensive evaluation,this paper explores the stability of the slope under the conditions of excavation,normal time,rainfall,earthquake and post rainfall earthquake under different slope excavation angles,and then introduces the fuzzy comprehensive evaluation method to comprehensively evaluate the slope of each excavation angle in combination with the excavation cost of each slope angle,Finally,the most suitable slope angle is obtained.The main research work and main conclusions and understandings are as follows:1.With the increase of slope angle,the potential sliding surface tends to move forward and become steeper.Under all working conditions,the safety factor of slope decreases nonlinearly with the increase of slope angle.After heavy rainfall,a transient saturation zone is formed on the surface of the slope,the strength of the soil in the saturation zone is greatly reduced,and the potential sliding surface of the slope moves from the deep layer to the shallow layer in the transient saturation zone.2.The rainfall infiltration results of slopes with different excavation angles are similar,while the saturated permeability coefficients of 9-2,W4 and W3 of slope soil layers are not different.However,the initial saturation of 9-2 and W3 soil layers is high,and the initial permeability coefficient is large.After 10 days of 150 mm rainfall,the maximum infiltration depth reaches about 7 m,the depth of transient saturation zone is about 3 m,and the initial natural saturation of W4 soil layer is only 0.45.After rainfall,the maximum infiltration depth is only 3m,and the maximum saturation depth does not exceed 1m.3.Under the earthquake and post rainfall earthquake conditions,the maximum horizontal displacement of the slope does not increase monotonically with the increase of the slope angle,but at the same height,the horizontal displacement increases gradually with the increase of the slope angle.Under low earthquake magnitude,rainfall has little effect on the safety factor of slope under earthquake.With the increase of earthquake magnitude,the gap between the safety factor of slope without rainfall and that of slope with rainfall gradually increases.4.Combined with the actual situation of the site,it is determined that the factor set affecting the slope excavation angle in the fuzzy comprehensive evaluation includes six factors: stability after excavation,stability under normal conditions,stability under earthquake,stability under rainfall,stability under earthquake after rainfall and excavation cost.And through the analytic hierarchy process,the weight vector W =(0.484 0.072 0.262 0.042 0.140)of the factor set is obtained.According to the calculation,the comprehensive value coefficients of each excavation angle from 25 degrees to 31 degrees are 1.919、2.153、1.996、1.330 and 1.234 respectively.After sorting,28 degrees is the most appropriate excavation slope angle.