Study On Embedded Depth Optimization Of Stabilizing Piles In The Jurassic Formation With Hard And Weak Bedrock Based On The Uncertainty Of Bedrock Parameters

The Jurassic strata is a typical weak mudstone and hard sandstone interbedded in Three Gorges Reservoir area,and its geological and mechanical characteristics are unique,and it is also a frequent area of landslides in the three gorges reservoir area.When the stabilizing piles are used to control the landslide in this area,the weak and hard interbedded strata in the bedrock are often ignored,it is assumed that the design calculation of homogenous bedrock can lead to a certain difference in results and make the governance project is not satisfactory.Therefore,this paper combines the three methods with the field investigation,physical model test and numerical simulation,the mechanical parameters distribution model of Jurassic strata in the three Gorges Reservoir area was established by field investigation and sampling,and based on the analysis,the stability analysis of landslide is carried out.Then the physical model and numerical simulation test are used to study the effect of the stabilizing piles on the anti-slide effect under the uncertainty of the parameters of the bedrock mass.And based on this,the embedded depth of the stabilizing piles in this kind of stratum is optimized,the modified safety factor of the embedded depth of the stabilizing piles is put forward.The main results are as follows:(1)Taking the Jurassic strata of Guizhou Town,Zigui County,Hubei Province as study area,through field investigation and field test,the rock mass characteristics development of the landslide bedrock in this area are studied.It is preliminarily proved that the landslide slide bed in this area has obvious stratification characteristics,and the springback value of rock mass is obtained by testing the springback value in the area,and the parameters of landslide bedrock in this area are preliminarily proved to have obvious uncertainty.(2)On the basis of field investigation,the elastic modulus and shear strength parameters of sandstone and argillaceous sandstone in this area are determined by indoor ultrasonic test,and the distribution model of rock mass mechanics parameters in this area is established.The stability of weak and hard interbedded bed rock slope is analyzed,the analysis formula of the slope stability coefficient in weak and hard interphase bedrock is established.Based on this,the model of 1/4 ellipsoid of three dimensional multilayer landslide is established,and the most dangerous sliding mass is determined under the condition of multiple distribution of landslide parameters,and the stress analysis model of soil arch behind pile is established,two new methods for calculating the minimum pile spacing of stabilizing pile are presented.It is found that two new calculation methods can save the used of stabilizing piles by more than 12%(3)According to the multi-condition physical model test frame of landslide-stabilizing pile,a test on deformation effect of stabilizing pile in weak and hard interbedded bedrock are established,and the numerical simulation test is also carried out by ABAQUS.By observing the deformation effect of the sliding mass and the displacement trend of the stabilizing pile,it is proved that the numerical simulation results are consistent with the physical model test results,the feasibility of numerical simulation test method is determined.By defining the bedrock thickness ratio ? and using numerical simulation to carry out numerical simulation tests under various bedrock conditions,the results show that the maximum displacement of the pile head decreases with the layer thickness ratio increased.When ? is less than 4,the maximum displacement of the piles decreases rapidly and then tends to smooth.When ? is greater than 4,the influence of the bedrock thickness ratio on the deformation of piles tends to a limit value.And when the stabilizing piles embedded the head bedrock is hard rock,the embedded effect of the stabilizing piles is better.With the increase of dip angle of bedrock,the maximum displacement of the pile head increases slowly first and then increases rapidly.When the elastic modulus ratio of weak and hard rock in the bedrock increased,the maximum displacement of the pile head shows the characteristics of the first rapid decline and then the gradual flattening.(4)On the basis of the feasibility and rationality of the above chapter,the effect of different embedded depth of stabilizing pile on the deformation effect of pile is studied with the bedrock as homogeneous hard rock.Based on this model,Orthogonal contrast test of different bedrock thickness ratio and different embedded depth of stabilizing piles in upper hard rock and lower weak rock were carried out.The optimum embedded depth of piles with different layer thickness ratio is determined,and the safety correction coefficient of the optimum embedded depth of piles is proposed.When the layer thickness ratio is fixed,only by changing the embedded depth of stabilizing pile can not strength the landslide,the influence degree of embedded depth on pile deformation has a limit state.