| The loess has a wide distribution in the middle and northwest of China.Under the guidance of China's western development strategy,the hydraulic engineering,highway engineering and railway engineering have developed at top speed which would naturally relate to the loess slope engineering.These slopes failure always presents the progressive failure characteristics,which will cause people's lives and property together with national economic construction severe damage.Therefore,clearly revealing the progressive failure mechanism of loess slope and proposing the loess slope stability analysis method considering the progressive failure characteristics are significance to the evaluation of loess slope stability and landslide forecast.The vector sum analysis method as a main line in this paper,first of all,the vector sum analysis method of loess slope stability considering the progressive failure characteristics is put forward.Within this framework,the structural loess slope stability vector sum analysis method is proposed under the influence of excavation unloading and water caused by structural deterioration considering the particularity of structural loess slope.And these methods considered the temporal-spatial distribution rule of parameters and the direction of the sliding force and sliding resistance force.Its rationality has large improvement than the traditional methods.The main results are as follows:(1)The vector sum analysis method of slope stability considering the progressive failure characteristics is proposed based on the distribution of shear strain increment and the evolution law of strength parameters of slip surface.Equivalent treatment method is proposed based on the spatial distribution law of strength parameters of slip surface,and the limit equilibrium analysis method of slope stability considering the progressive failure characteristics is put forward by means of the equivalent strength parameters.Comparative analysis of the slip surface and the evolution process of safety factor determined by two methods,the reliability of the vector sum analysis method of slope stability considering the progressive failure characteristics is verified.Based on this method,the framework of the effective simulation and evaluation of landslide multi-stage destruction is established.For a landslide in low-rent housing area of Dangjiaba in Xunyang country,the formation process of multi-slip surfaces and interaction is revealed through the progressive evoluation law of plastic shear strain,plastic tensile strain,shear strain increment,material parameter and safety factor of vector sum method.Comparative analysis of the calculation results with the field investigation results,the reliability of the framework is verified.(2)Inspired by slope progressive failure process,in order to solve the reasonable determination of double reduction coefficients existing in the double reduction coefficients method,a case study of strength parameter distribution obeying the linear attenuation assumption,a non-proportional relationship between the reduction coefficient of cohesion and the reduction coefficient of internal friction angle is established.The comprehensive safety factor with the contribution of shear strength parameter to sliding resistance force as weight is proposed in order to evaluate the overall safety reserve of slope.The non-proportional relationship is brought to the traditional strength reduction finite element method to propose the non-proportional correlative reduction finite element method for strength parameters.To verify the rationality of this method,non-proportional relationship is brought to the simplified Bishop's slice method and put forward the non-proportional double safety factors of Bishop's slice method.Combined with an example,comparative analysis of two slope stability analysis methods and three reduction ways corresponding results,the rationality of the non-proportional correlative reduction finite element method for strength parameters is verified.Comparative analysis of the calculated results of existing comprehensive safety factor with the calculated results of comprehensive safety factor proposed in this paper,the comprehensive safety factor proposed in this paper not only has clear physical meaning,but also has strong practical value.(3)The initial structural parameter of loess is expressed as the function between mass water content and confining pressure.The structural parameter of loess is expressed as the function between initial structural parameter and generalized shear strain.The structural parameter of loess is introduced to the elastic-plastic model based on the Mohr-Coulomb yield criterion.The simulation method of loess slope progressive failure under the excavation unloading condition considering the initial structural parameter is successfully realized by the secondary development platform of ABAQUS.Based on this method,the progressive failure law of structural loess with different mass water content,different modulus magnification and excavation angle under the excavation unloading condition is studied.According to these calculation results from the simulation method,the limit equilibrium method,the strength reduction method and the vector sum method of loess slope stability analysis considering the initial structural parameter are proposed.By comparative analysis of the results determined by three loess slope stability analysis methods,the reliability and rationality of vector sum method of the loess slope stability analysis considering the initial structural parameter are verified.(4)First of all,the coupled analysis of transient unsaturated seepage-stress is done based on the double-stress variables theory of Fredlund.Secondly,the matrix suction's contribution to the strength is considered as a part of the cohesion and then the spatial distribution law of slope strength parameters is obtained.Thirdly,the program of vector sum method of unsaturated soil slope stability analysis subjected to transient seepage based on the temporal-spatial distribution of strength parameters of slip surface has been developed by using Matlab platform.These processes formed a set of vector sum method of unsaturated soil slope stability analysis accounting for seepage,deformation and stability simultaneously.Finally,taking the influence of drawdown of reservoir water level on slope stability of embankment for example,comparative analysis of proposed method with the traditional method,the rationality of vector sum method of unsaturated soil slope stability analysis subjected to transient seepage is verified.(5)Taking the stability analysis of the structural loess slope under the condition of raising the ground water level for example,based on the dynamic seepage field of slope,deformation parameters and strength parameters of soil is constantly changed according to the structural deterioration equation caused by water during the calculation process and the seepage force is dynamic updated according to the seepage gradient of gauss integral point.With the help of body force method,the vector sum method of the structural loess slope stability analysis is proposed based on the temporal-spatial evolution law of effective density,elastic modulus,Poisson's ratio,cohesion,internal friction angle and seepage force.Comparative analysis of the calculated results determined by the limit equilibrium method(Bishop's method)of the structural loess slope stability analysis based on the temporal-spatial evolution law of parameters,the rationality and reliability of structural loess slope stability analysis based on the temporal-spatial evolution law of parameters are verified. |
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