Estimation Of Shear Strength Of Slip Zone Solis In Middle Jurassic Red Beds In Wanzhou Reservior Area

The landslide distributed in Jurassic red beds is an important type of geological disaster in the Three Gorges reservoir area.It is widely distributed,has a large scale,and has serious damage.According to the geological and disaster investigation data from the second and third phases of the Three Gorges Reservoir?TGR?area,more than 70%of the landslides in the reservoir area are the red-bed landslides,such as the Qianjiangping landslide,Chongqing Iron and Steel Landslide,and Yunyang Jipazi landslide.In the?TGR?area,deformation of slope and instability of landslide causes direct loss of residents and buildings on the landslide.When the slope enters into the river,it can clog river and cause tusnamis.Tsunamis generated by landslides pose a very dangerous threat to dam structures,agricultural areas,coastal properties,and human communities living on the shorelines of seas,rivers and artificial reservoirs.For example,in June 2003,the Qianjiangping landslides slipped into river,leading 1,200 people to homelessness,24deaths,19 injuries,and direct economic losses of more than 57.36 million yuan.In order to prevent the above tragedies from happening again and adapt to the rapid development of land use,it is necessary to evaluate the stability of the Jurassic red-bed landslide in the Three Gorges reservoir area as well as the engineering management.In the evaluation and control of slope stability,selecting reasonable shear strength parameters?c,??of slip zone not only has a direct impact on the stability of slope management,but also has a direct control over the economic costs of slope management.Therefore,it is of great practical significance to carry out an in-depth and systematic study of the c and?values of the slip zone in the Jurassic red-bed landslide.This study takes the Jurassic red-bed landslide in the reservoir area of Wanzhou District as the research object.Based on statistical analysis of the distribution and development characteristics of the red-bed landslides in the study area,the mathematical statistics,?² test,and the method of optimal fitting are used to evaluated the random distribution of shear strength parameters of the sliding zone soil of landslide in Middle Jurassic red bed in the reservoir area of Wanzhou.Based on mathematical statistics,using Support Vector Machine and Kriging interpolation method to study the c,?value of the impact factor and establish its prediction model.Through the above research,the research results are mainly shown as following.?1?The distribution and development characteristics of Jurassic red beds landslides in the reservoirarea of Wanzhou were obtained through mathematical statistics and empirical analysis.The statistical landslide samples are mainly distributed on the mainstream of the Yangtze River and the main tributaries.The study area is a typical red layer development area.The landslides are mainly developed in the Jurassic middle Shaximiao Formation,and the lithologies are mainly composed of mudstones and sandstone interbedded.The main materials of slip body are Quaternary residual strata,collapse plies,and landslide accretion layers,which are mainly naturally formed accretion landslides.The front elevation of 60%of the statistical sample landslide is lower than175m.hence,the landslide basics in the study area are partially subwater landslides,and these landslides will be affected by the erosion and infiltration of the reservoir water in the process of impounding water.According the scale of the landslides,landslides of the bank sections will be mainly developed for medium and large-scale landslides.According to the thickness,the study area will mainly develop mid-level landslides.Accounting for72.3%of the statistical sample landslides;the area mainly develops progressively near-horizontal horizontal layered slopes and reversed slopes,and the profile shapes are mainly convex and stepped.?2?The random distributions of shear strength of slip zone soil with similar characteristics are estimated by Studying 44 landslides with similar engineering geological conditions in the middle Jurassic Shaximiao Formation in Wanzhouku reservoir section.The main materials of slide zone soil are grayish white silty clay and silty clay crushing gravel breccia.The minerals of slide zone soil are mainly feldspar,illite,quartz and a large amount of montmorillonite.The slide zone minerals have certain oriented arrangement,and clay minerals mainly were observed in the form of flakes.The scratches in the clay are smooth,flat and orderly;the chemical composition of the slide soil is mainly SiO₂,Al₂O₃,Fe₂O₃,K₂O,MgO,CaO,Na₂O and H₂O^-??3?The probability distribution of landslide-soil shear strength parameters in the study area is mainly based on four steps:data collection,empirical model assumption,parameter estimation,and probable model test.Using histogram estimation and reference to previous research results,assume that the empirical distributions of c and?values are normal distributions,lognormal distributions,and Beta distributions.The?² test method was used to test the hypothesis of the overall experience distribution.The test results showed that:?a?The overall random distribution of internal friction angles accepts the assumption of normal distribution,rejects the assumption of lognormal distribution and Beta distribution;?b?The distribution form of cohesion accepts the log-normal distribution hypothesis and rejects the normal distribution hypothesis;?c?The random distribution form of the peak of the saturation cohesion accepts the hypothesis of the log-normal distribution and accepts the Beta distribution hypothesis.Through the limited comparison method,comparative analysis of the assumption of the distribution model found that the degree of acceptance of the normal distribution of the internal friction angle of the sliding zone is the best,and the optimal fitting model of the ₁c,c₂,and c₄ is logarithmic normal.₃c agrees with the beta distribution best.Based on the above,the probability density function of shear strength parameters of Jurassic red landslides in Wanzhou District proposed in this paper can be used to analyze the failure probability of landslides with similar geological features in the same area.?4?From the point of view of mathematical statistics,the influence factors of the shear strength parameters of sliding zone soil are discussed in detail.The basic physical and mechanical parameters of the landslide have significant correlation with the shear strength parameters of the landslide zone,but the landslide size parameters have no significant effect on the shear strength parameters.Based on the Matlab software programming,a Support Vector Machine model?SVM?was used to establish a predictive model for the shear strength parameters of the slip zone of the Jurassic red bedslide in the red bed of the reservoir bank.And an example landslide was selected to conduct an example test for its accuracy and applicability.For the prediction model of sliding zone soil cohesion,the average absolute error is between 2.58kPa and 3.67kPa.For the cohesion force internal friction angle,the average absolute error is between 0.32°and1.64°.Taking the Wanquan landslide as an example,the natural cohesive force peaks of sliding zone soil,the peak value of natural internal friction angle,the peak value of saturated cohesion force,the peak value of saturated internal friction angle,the residual value of saturated cohesion and the saturated internal friction are used in this prediction model.The residual value of the angle is predicted,and the prediction result is compared with the actual value.The comparison result shows that the relative error is about 5%,and the prediction accuracy is better and has better applicability.?5?In this study,the comprehensive selection value or back analysis value of the shear strength parameters of the landslide in 77 natural landslides under natural conditions is collected,and the shear strength of 80%of the sample landslides in the study area is measured by the Kriging interpolation method.The spatial distribution of the shear strength parameters of landslides was predicted.The prediction results are represented by the regional distribution prediction maps for the values of c and?.The 20%test data is used to test the prediction model.The average absolute error of c value is 2.24kPa,and the average absolute error of?value is 1.2°.The credibility of the prediction model is relatively high.