Non Equal Proportion Related Non Synchronous Strength Reduction Method For Loess Slope Stability

The disaster caused by slope instability is one of the three major geological disasters in the world.It is often ravines and forms a large number of slopes.During to the loose structure and large pores of loess,the stability of slope is generally poor.With the continuous increase of engineering construction in China,the stability of slope under the static and dynamic action is related to the personal safety.Because the research on this is not perfect at present,it is important theoretical significance and engineering application value.At present,the most common methods of slope stability analysis are limited equilibrium method.The safety factors defined by the two definitions can be attributed to the reduction factors of two strength parameters,cohesion and internal friction angle,when each point on the failure surface reaches the limit state.In general,the two methods are based on the premise that cohesion and internal friction angle have the same strength reserve.However,the cohesion and internal friction angle of the sliding surface soil have different stages and degrees,and their safety reserves should also be different.From the physical mechanism,the failure of the slope is not an instant,but a gradual development process.Therefore,based on the strength reduction method of finite element,the non-equal ratio example strength reduction method of finite element is proposed,at the same time,the non-equal ratio strength reduction technology is adopted for the two parameters.It makes the relationship between the size of the slope safety factor and the two reduction factors become a difficult problem.Therefore,according to the elastic theory,people put forward a method to determine the safety factor based on the contribution proportion of the two strength parameters in the slope stability analysis,which is called the finite element two parameter non proportional correlation strength reduction method.A large number of experiments have further confirmed that in the process of slope transition from stability to instability,the order of strength parameter reduction loss is also different.For loess slope,the initial stage of slope deformation is mainly the reduction of cohesion on potential sliding surface.This paper presents a new method to reflect the reduction problem of the shear strength parameters with different proportion and different time step.The main work and achievements are as follows:(1)By studying the attenuation law of shear strength index of structural loess,it is found that the attenuation mechanism,proportion,rate and sequence of cohesion and internal friction angle are different in the failure process of loess slope,that is,for different soil slopes,the attenuation of cohesion and internal friction angle is different The attenuation speed of structural loess is much faster than that of structural loess,while that of sandy soil will decline rapidly.(2)This paper puts forward the method of two parameter non equal proportion related non synchronous strength reduction,and deduces the non equal proportion relation between cohesion reduction coefficient and internal friction angle.ABAQUS finite element calculation software was developed twice,and a more reasonable method of slope stability analysis is realized,that is,the method of finite element non equal proportion related non synchronous strength reduction Program operation.(3)The results of different strength reduction methods for slope stability analysis are compared with the results of geo studio rigid body limit equilibrium analysis method.The results show that the position and shape of plastic cloud chart slip arc determined by non-homogeneous and non-homogeneous slope reduction are similar to those obtained by other methods,and the obtained results are safe The errors of coefficient and other finite element methods are 0.38%,0.59%and 1.15%respectively,and the error of limit equilibrium method is the smallest(0.19%).The inhomogeneous model also conforms to this law,thus verifying the rationality and reliability of the two parameter non proportional correlation non synchronous strength reduction method.(4)Under normal conditions,the stability of natural loess slope is weaker than that of filling loess slope;under rainfall conditions,due to the weakening of rainfall infiltration on Loess Strength,the stability of loess slope after rainfall is weaker than that former rainfall,and with the increase of rainfall time,the stability of loess slope decreases,when the rainfall time is 72 hours(the average rainfall intensity is 110 mm/d),the natural loess slope is damaged,and the filled loess slope is still stable;under the earthquake condition,due to the influence of inertia force on the loess slope,the stability of the loess slope after the earthquake is lower than that before the earthquake,and with the increase of the earthquake acceleration,the stability of the loess slope decreases;through the analysis of different levels of earthquake acceleration downhill displacement nephogram and the relation curve between safety factor and seismic acceleration show that when the horizontal seismic acceleration is 0.125g and 0.075g respectively,the natural loess slope is unstable and the filled loess slope is stable.When the horizontal seismic acceleration is 0.175g and 0.2g,the filled loess slope is also unstable.