Study On The Interaction Between Anti-slide Pile And Embedded Rock Mass Under The Condition Of Soft And Hard Interphase Strata

For a long time,the geological disaster of landslide in the Three Gorges Reservoir area has been widely concerned at home and abroad.Most of the landslides are distributed in the sedimentary rock area,in which the sliding bed is a composite near horizontal layered rock mass mainly developed in the Jurassic strata,which often results in the condition that the anti-sliding pile embedded section is located in the multi-layered composite rock body in the slope reinforcement and slope control projects.In the design guide and textbook,the multi-layer rock mass of sliding bed is equivalent to homogeneous rock mass or the traditional method such as ground coefficient area change algorithm is recommended to calculate the internal force of pile body.The calculation formula is complex and not easy to understand and accept.Considering the influence of different lithology characteristics of sliding bed on the mechanical characteristics of sliding pile,the research results are not deep enough.The Jurassic stratum in the reservoir area is a typical soft hard alternating stratum of sandstone and mudstone.In this paper,a mechanical model is established on the basis of a landslide treatment project in the Three Gorges Reservoir area,combined with the calculation method of elastic foundation beam as the theoretical basis,and considering the principle that the calculation operation is simple and easy to accept,based on the principle of pile deformation coordination at the interlayer boundary of sliding bed rock mass,through the establishment of interlayer boundary In order to ensure the continuity of internal force and deformation of pile body,the deformation coordination equation is studied by theoretical analysis and numerical simulation analysis.The main work and results are as follows:(1)This paper summarizes the traditional design and calculation method of anti-slide pile,distribution form of landslide thrust,pile position and pile spacing,determination method of design parameters and shortcomings,which provides reference for the establishment of mechanical model and calculation of internal force and deformation of anti-slide pile.(2)Based on the shortcomings of traditional methods,the mechanical model of elastic anti slide pile embedded in various strata is established.Considering the continuity of internal force and deformation at the interlayer boundary of sliding bed rock,the internal force calculation formula of anti-slide pile under three different constraints is obtained.(3)Based on the research background of the soft and hard interbedded strata composed of sand and mudstone in a landslide treatment project in the Three Gorges Reservoir Area,this set of numerical simulation analysis model under the geomechanical parameters is established,and on this basis,according to the different mechanical properties of the rock mass in the sliding bed,It can be generalized into six cases: all-soft rock,all-hard rock,soft-hard layer,hard-soft layer,soft-hard layer,and hard-soft layer.The results show that the change of the thickness ratio of the lower layer has a great influence on the mechanical characteristics of the anti-slide pile body:(1)with the increase of the thickness ratio of the layer,the soft-hard layers and the soft-hard layers interact with each other Under the form of layer distribution,the mechanical properties of antislide pile are close to homogeneous hard rock,at this time,hard rock is the main factor affecting the bending moment and shear force of pile shaft,and the maximum bending moment and shear force of pile shaft increase first and then decrease,and the displacement of pile shaft decreases continuously rule;(2)with the decrease of layer thickness ratio,the hard-soft layers and the hard-soft layers interact with each other Under the form of layer distribution,the mechanical properties of anti-slide pile are close to homogeneous soft rock,at this time,soft rock is the main factor affecting the bending moment and shear force of pile body,and the maximum bending moment and shear force of pile decrease first and then increase,and the displacement of pile body increases continuously.In view of this,if multiple layers of rock mass are considered as homogeneous hard rock,the longitudinal reinforcement and stirrup required for reinforcement in the pile body are relatively small in design,which is easy to cause insufficient anti sliding force;if multiple layers of rock mass are considered as homogeneous soft rock,the longitudinal reinforcement and stirrup required for reinforcement in the pile body are relatively large in design,which is easy to cause capital waste.Therefore,when dealing with the landslide in this area and the multi-layer rock mass of the sliding bed,we should fully consider the influence of the thickness ratio of the lower layer of the different distribution forms of the sliding bed rock mass on the stress characteristics of the anti-sliding pile.(4)Under the condition of different lithology combination of the sliding bed,when the layer thickness ratio is fixed,the bending moment and shear force of the bearing section of the pile body are not affected.The maximum displacement value of the pile top,the maximum shear force value of the pile body and the maximum bending moment value of the pile body are arranged from small to large in the order of: hard-soft layering<hard-soft interlayer < soft-hard interlayer < soft-hard layering,the maximum change range is respectively as follows: 17.1%、11.3%、15.2%.Therefore,in the design of antislide pile,the influence of different lithology combination of slide bed on the internal force and deformation of slide pile should be considered.(5)Based on the numerical model established under the geological parameters of the above actual working conditions,the resistance coefficient of the foundation applicable to the layer strip is obtained,and MATLAB is used by comparing the field monitoring data with the theoretical calculation results and numerical simulation results,the rationality of theoretical derivation and the correctness of numerical model establishment under the mechanical model are verified.In view of the above rationality,the results of numerical simulation are compared with the methods in this paper,the area change algorithm of foundation coefficient and the traditional k-method,and the feasibility of the research results in this paper is further illustrated.