用有限元法研究降雨对青海云杉林边坡稳定性的影响

Effect of rainfall on slope stability of Picea crassifolia forest based on finite element method in Qinghai

为研究降雨强度和降雨历时对贺兰山青海云杉林边坡稳定性的影响,通过三轴压缩、饱和渗透等土工试验获取青海云杉林边坡根土复合体的土力学参数,在此基础上建立基于有限元的贺兰山青海云杉林边坡稳定性计算模型。利用该模型分析了青海云杉林边坡与无林边坡(对照)的安全系数和破坏时间随降雨强度、降雨历时、边坡坡度的变化规律,拟合了降雨强度与边坡破坏时间的回归模型。通过降雨条件下青海云杉林边坡和无林边坡破坏时的最大位移、最大塑性应变的分析,量化了贺兰山青海云杉林增强降雨边坡稳定性的程度。研究结果表明:贺兰山青海云杉林与无林边坡的安全系数随降雨历时、降雨强度、边坡坡度的增加而减小。降雨条件下,青海云杉林边坡的破坏时间要显著高于无林边坡(平均高出48.61%),降雨强度与破坏时间的回归关系满足幂函数;青海云杉林的固土护坡作用随降雨强度的增加(从10 mm/h增加到25 mm/h)而减弱(从53.20%降低到45.70%),青海云杉林可以明显提高边坡破坏时的最大位移(提高224.42%)和最大塑性应变(提高95.28%)。综上,青海云杉林显著增强了降雨边坡的稳定性。

[Background]Helan Mountain is an ecological barrier and water conservation area of Yinchuan Plain,and it is also a serious area of soil and water loss.The geological disasters,such as debris flow and shallow landslide caused by strong rain intensity,have caused huge economic,cultural and ecological losses in this area.Therefore,the study of slope stability under extreme weather is of great significance to the economic and social development in Helan Mountainous area.[Methods]In order to study the effect of rainfall intensity and duration on the slope stability of Picea crassifolia forest in Helan Mountain,the geomechanical parameters of the root-soil composite of P.crassifolia were obtained by triaxial compression,saturated infiltration and other geotechnical tests.On this basis,the stability calculation model of P.crassifolia forest slope in Helan Mountain was established based on finite element theory and software(ABAQUS).The finite element model for stability calculation of P.crassifolia forest slope was used to calculate the variation of safety factor(Fs)and the duration at failures(tf)with the rainfall duration under different rainfall intensity(i=10-25 mm/h),and the intensity and duration at failures regression(ID)was fitted.Based on the analysis of maximum displacement(Umax)and maximum plastic strain(PEMAGmax)during the slopes without and with trees failure induced by the rainfall,the degree of slope stability improvement by the root-soil composite of P.crassifolia forest in Helan Mountain was quantified.[Results]1)The safety factors of the slopes without and with trees decreased with the increase of rainfall duration,rainfall intensity and slope grade.The duration at failures of P.crassifolia forest slope under rainfall was significantly longer than that of the slope without trees(the average increase was 48.61%),and the regression relation between rainfall intensity and duration at failures satisfied the power function(The ID regression model:i=262.4 tf-0.998,R2=0.9996(slope without trees);i=328.7 tf-0.945,R2=0.999(slope with trees)).2)Under rainfall conditions,because of the effect of vegetation,the growth rate of duration at failures were 53.20%(i=10 mm/h),50.57%(i=15 mm/h),44.96%(i=20 mm/h)and 45.70%(i=25 mm/h)respectively and the average was48.61%,however,the effect of root reinforcement on the slope decreased from 53.20%to 45.70%.The P.crassifolia forest obviously increased the maximum displacement Umax(224.42±80.29)%and the maximum plastic strain PEMAGmax(95.28±33.74)%when the slope failed.[Conclusions]The ID regression model,the maximum displacement and the maximum plastic strain of slopes without and with trees are obtained under rainfall,which prove that the P.crassifolia forest in Helan Mountain significantly enhances the slope stability.