| Slope stability is one of the three classic problems in geotechnical engineering.How to accurately and effectively evaluate the stability of engineering slopes has always been a focus of attention in the engineering community,and is also a prerequisite for landslide disaster prevention and control.The strength criterion is the theoretical basis for determining whether geotechnical materials have reached the limit state.The Mohr Coulomb criterion is widely used in geotechnical materials due to its simplicity,but it ignores the influence of intermediate principal stress on the strength criterion of geotechnical materials.The geotechnical material criteria that consider the intermediate principal stress include: unified yield strength theory,SMP criterion,etc.The Mohr Coulomb criterion can be regarded as an inscribed polygon of the SMP criterion on the off plane,which is the lower limit of the SMP criterion.The slope stability coefficient calculated using the Mohr Coulomb criterion tends to be conservative.Due to the influence of rainfall and changes in groundwater level,the water content in soil slopes is in a fluctuating state,and the soil is often in an unsaturated state.Sudden drawdown of reservoir water level and rainfall,especially rainstorm,are the main factors inducing geological disasters such as dam break and landslide.The boundary of rainfall infiltration into soil slopes is a changing boundary.When rainfall is low,the infiltration boundary of rainfall is the flow boundary;When the rainfall is large,the infiltration boundary of rainfall is the pressure head boundary.The reasonable description of rainfall infiltration boundary is one of the key issues in the coupled finite element analysis of soil slope seepage field and stress field.Due to the varying intensity of actual rainfall,the processing of rainfall infiltration boundary conditions in numerical calculations is relatively cumbersome.Applying the SMP criterion considering the principal stress to the stability analysis of three-dimensional slopes and unsaturated soil slopes,using a processing method that can simulate the infiltration boundary of rainfall in a real way,is of great significance for predicting the stability of slopes under real stress conditions and ensuring engineering safety.Based on the ABAQUS software platform,and the UMAT subroutine is written to achieve the secondary development of the SMP strength criterion.Based on classic slope examples,the differences between the SMP strength criterion and the Mohr Coulomb strength criterion were compared and analyzed from multiple perspectives such as stress,plastic zone development,and safety factor.The stability problems of two-dimensional and three-dimensional slopes under rainfall infiltration conditions and reservoir water level fluctuations were systematically studied.The "air unit method" was used to simulate the infiltration boundary of rainfall,and numerical simulations were carried out for three types of transient saturation zones: upward,suspended,and downward under different rainfall conditions.The distribution of pore water pressure,development of plastic zone,and changes in safety coefficient of the slope were obtained.The "air unit method" was used to simulate the infiltration boundary of rainfall,and numerical simulations were carried out for three types of transient saturation zones: upward,suspended,and downward under different rainfall conditions.The distribution of pore water pressure,development of plastic zone,and changes in safety factor of the slope were obtained.Considering the synergistic effect of seepage force inside the slope and water pressure outside the slope.And the changes in pore water pressure and seepage vector during the rise and fall of reservoir water level were studied.Finally,the SMP criterion was applied to the stability analysis of three-dimensional slopes,under rainfall infiltration conditions,and under reservoir water level fluctuations,and the role of intermediate principal stress was analyzed.The main research results of this article are as follows:(1)Selecting cube elements,Yu Maohong’s classic slope,and Fei Kang’s rainfall slope as calculation models to verify the SMP criterion calculation results.The comparison results preliminarily indicate the correctness of the subroutine developed in this article.In order to further verify the rationality of the subroutine,the stability of three-dimensional slopes,slopes under rainfall conditions,and slopes with dynamic water levels were studied.And analyzed the changes in their plastic zone,horizontal displacement,and safety factor.The results show that the critical plastic strain zone and horizontal displacement of the slope obtained using the SMP criterion are smaller than those obtained using the Mohr Coulomb criterion,and the slope safety factor increases by 10% to 15%.The result based on the SMP criterion is equal to the result when the intermediate principal stress coefficient is 0.5 in Yu Maohong’s unified strength theory.(2)Using the "air element method" to simulate the boundary conditions of slope rainfall infiltration.Apply free seepage boundaries at both ends of the unit to achieve slope runoff,while ignoring the influence of the thickness of the "air unit" on the calculation results.In order to effectively consider the convergence of the calculation results,the elastic modulus of the "air element" is taken as one tenth of the soil mass,and the permeability coefficient is taken as 100 times the soil mass.The comparative analysis results with the classic heavy rainfall infiltration slope model indicate that the use of the "air unit" will affect the development of the plastic zone at the top of the slope.However,the difference in the slope safety factor and the entire sliding zone obtained by the two methods is not significant,indicating that this method has good rationality.(3)Based on the ABAQUS platform,the numerical simulation of transient saturation zones of upward,suspended,and downward movement within slopes during rainfall was achieved.And it was extended to the three-dimensional slope model to achieve stability analysis of the three-dimensional slope under rainfall conditions.The results indicate that the form of transient saturation zone is closely related to the soil water characteristic curve of the soil.The higher the permeability of soil,the faster the infiltration of rainwater,and the easier it is to form an ascending transient saturation zone.The safety factor of the slope gradually decreases with the continuous rainfall,and the greater the rainfall intensity,the smaller the safety factor.The ability of the suspended transient saturation zone to weaken the shear strength of the soil shows a trend of first increasing and then decreasing.Ignoring the three-dimensional effect of the slope,the safety factor of the slope will be underestimated by 10% to 18%.The slope safety factor improved by 10.57% after rainfall based on the SMP criterion.(4)Considering the influence of alternating changes in static water pressure outside the slope and pore water pressure inside the slope,the variation laws of pore water pressure and slope safety factor during the rise and fall of reservoir water level under two rate conditions of1 m/d and 0.1 m/d were studied.The results show that when the water level rises,there is both seepage force and hydrostatic pressure pointing towards the inside of the slope.The water level inside the slope increases with the water level outside the slope,and the groundwater level line inside the slope shows an inward concave shape.At this point,the safety factor of the slope increases as the water level rises.After the reservoir water level drops,groundwater is continuously discharged.The groundwater level at the front edge of the slope is significantly affected by the decrease in reservoir water level,while the influence of the position of the rear edge is relatively small.The groundwater level line inside the slope shows an upward convex shape.The slope safety factor increased by 13.44% after a sudden drop in reservoir water level based on the SMP criterion. |
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