| Linshui-Baer landslide is located at Baer Town Village,Linshui County,Guang'an City,Sichuan province.The unique characteristic of Linshui-Baer landslide distinguished from other landslides is that it is a plane turning composite landslide,which is composed of H2 landslide located at the upper part and the H1 landslide located at the lower part,with a large angle between the main sliding directions of the two landslides.The field investigation shows that the deformation is very obvious as there are a large number of surface tension and shear cracks,and the landslide is susceptive to slip under the condition of rainfall and so on.Based on the detailed investigation of the landslide area and the laboratory tests on the rock and soil samples from the landslide,in this paper,firstly,the basic characteristics of Linshui-Baer landslide was summarized,and the stability and deformation failure mode of landslide were analyzed qualitatively.Then,two-dimensional stability of the selected the main sections of HI and H2 landslides,by using the traditional limit equilibrium method,were evaluated.Finally,numerical simulation analysis of the entire landslide was carried out by FLAC3D,and three-dimensional safety factor was obtained by the strength reduction method.In this process,through a simple example of a homogeneous soil slope,the instability criterions and influencing factors in the process of solving slope safety factor by strength reduction method in FLAC3D were discussed separately.The main conclusions are as follows:(1)Linshui-Baer landslide is mainly composed of H2 landslide located at the upper part and H1 landslide located at the lower part.The front part of H1 landslide,closing to the gully,collapsed,and tensile cracks occurred at the trailing edge of the landslide,all of which indicate that HI landslide is a typical traction type landslide.Under the traction effect of H1 landslide,H2 landslide slid,and there was an obvious boundary between strong and weak deformation zone in H2 landslide.(2)The entire thickness of Linshui-Baer landslide body is relatively thin,and the sliding bed is composed of mudstone and shale,which are impervious.Under the condition of rainfall,groundwater easily flows along the interface between the sliding body and bedrock,which will significantly reduce the shear strength of rock and soil.It is speculated that rainfall is the main trigger factor leading to landslide instability.(3)The stability of each section of HI and H2 landslide was analyzed by limit equilibrium method.The strong deformation zone of HI landslide and H2 landslide is in a stable state under the natural condition,and in a state of less stable or instable under the condition of rainstorm and earthquake.The weak deformation zone of H2 landslide is in a stable state under the natural condition and the earthquake condition,and in a less stable state under the rainstorm condition.Comparing the results of various limit equilibrium methods,it can be found that the stability coefficient roughly conforms to the following rules:Janbu method<Ordinary method<Spencer method<M-P method<Transfer coefficient method<Bishop method.Although there are some differences in the stability coefficients from the various methods,the stability of the landslides in various conditions is basically the same.(4)Taking a simple homogeneous soil slope as example,the stability of the slope was evaluated by FLAC3D software basing on the different failure criterion,i.e.the convergence of numerical computation criterion,the connectivity of plastic zone criterion,the mutation of displacement criterion,and the safety factors for the three criteria are 1.62,1.59 and 1.60 respectively.The three criteria have their own advantages and disadvantages,and have significant internal relations.In the practical application,the criterion of numerical computation non-convergence by FLAC3D default is recommended,at the same time,the distribution of plastic zone and the change of displacement should be took account,so as to make a comprehensive judgment on whether the slope has been in a critical state of instability.(5)Based on the above example,the influence of rock and soil parameters on slope safety factor is studied.The change of dilatancy angle will influence the stability of the slope,for when dilatancy angle changes from 0°to 5°,the safety factor experienced significant changes from 1.62 to 1.65,while the effect of tensile strength is very small.A reduction algorithm for bulk modulus and shear modulus is proposed for FLAC3D strength reduction method.When solving the safety factor by FLAC3D,the associated flow rule should be used and appropriate dilatancy angle for the rock and soil material should be given,which can make the calculation result more reliable.Adjusting bulk modulus and shear modulus have little effect on the safety factor,but it can significantly change the deformation and displacement of the slope.(6)H1 landslide is simulated by FLAC3D software alone.The safety factor obtained by the strength reduction method is closer to the result of the limit equilibrium method.The failure of the landslide occurred mainly in the front of the slope.The rear of the landslide is always in steady state under various conditions.(7)The real three-dimensional geological model Linshui-Baer landslide was established by FLAC3D,considering the sidewall friction resistance and the interaction between H1 and H2 landslide,and the results show that the overall stability of the landslide is significantly higher than the two-dimensional calculation.The interaction between H1 and H2 landslide is obvious,and the overall deformation and failure of Linshui-Baer landslide is the result of the deformation coordination between the two landslides.The sliding of H1 landslide is the result of the combined effect of its own sliding force and the H2 slide thrust,and the sliding direction is affected by the relationship between the two forces.Compared with the single simulation of H1 landslide,the sliding range of H1 landslide is obviously expansive under the heavy rain condition,which has developed to the middle part of the landslide.Due to the rear blocking effect and the front traction effect of H1 landslide,the sliding direction of H2 landslide is significantly deflected toward the left side of free face. |
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