Research On Dynamic Response Of Pile-anchor Support System For Bedding Rock Slope Under Earthquake

China locates in two major earthquake zones.In recent years,earthquakes have occurred frequently in western China.Therefore,in the construction of mountainous cities,not only the spatial relationship and interaction between buildings and slopes should be considered,but also the impact of earthquake should be taken into account.In this way,it can ensure that the buildings and sites have sufficient seismic performance.Studying the seismic dynamic response of this phenomenon can promote the understanding of the seismic response law of buildings and slope sites.Meanwhile,it is helpful to put a reasonable seismic design scheme for building foundation and slope supports.This paper based on the project named "Study on 2.5D Dynamic Stability of Anchoring Slope and Seismic Mechanism of Adaptive Anchor Cable”,and "Research on the Key Technology of the Interaction between the Stability of the Mountain Building Site and the Structure Fixed End under the Seismic Effect",which are respectively held by National Natural Science Foundation of China and CISDI Engineering Co.,Ltd.The seismic dynamic response of bedding rock slope with building pile foundation supported by prestressed pile-anchor is studied.The main research contents and conclusions are as follows:(1)Analyzing the characteristics of anchor cable under earthquake,the axial force of the free section of the anchor cable under earthquake is regarded as different initial prestress,based on the Kelvin model,the solution of shear stress and axial force of the prestressed anchor cable is derived,and the deduced formulas are verified through an example.The influence of elastic modulus and Poisson’s ratio of rock,diameter of anchor solid of the shear stress and axial force are analyzed.Results show that the shear stress and axial force of the anchorage section increase with the axial force of the free section under earthquake.The larger the elastic modulus of rock mass or the smaller the diameter of the anchor hole,the larger the shear stress peak value of the anchorage section is,and the position of the peak value is more concentrated near the initial point of the anchorage section.(2)A shaking table test is carried out for the bedding rock slope,earthquake with different types and amplitudes are input to the model.The seismic dynamic response of the system is studied mainly include the strain of prestressed anchor cable and building pile foundation,the displacement of anti-slide pile and the acceleration response of slope.The results indicate that the strain of the anchor cable changes with the seismic wave,and the strain of the anchor cable reaches the maximum when the seismic wave reaches the peak,the upper cable force is larger than the lower one under earthquake.When the seismic amplitude increases,the upper anchor cable slips and losts anchor effect.The maximum strain of building pile foundation is located at a certain depth below the sliding surface,and the stress of building pile foundation far away from the slope is greater than the one near the slope.The peak accelerations of slope top increase linearly with the seismic amplitude,but under the condition of Wenchuan wave with 0.55 g amplitude and sine wave with 0.4g amplitude,the peak acceleration at each point has a tendency to decrease.With the increase of seismic amplitude,the peak acceleration amplification coefficient of each points under Wenchuan and Sine earthquake does not change monotone,but decreases first and then increases.(3)Using finite difference program to establish three numerical simulation model and study the response of the axial force of anchor cable,horizontal displacement and acceleration response of anti-slide pile and slope.By comparing the results,it can be seen that the prestressed pile-anchor system limits the elevation amplification effect and the whipping effect of the slope,and reduces the displacement of the slope surface,the slope top and the left and right sides of the structural plane.Under the support of pile-anchor system,the stress of prestressed anchor cable is always larger in the upper part and smaller in the lower one of slope with building pile foundation.Under natural earthquake,for the slope without building pile foundation,when the seismic amplitude is small,the stress relation of the anchor cable is larger at the bottom and smaller at the top;when the seismic amplitude increases,the stress relation of the anchor cable is larger at the top and smaller at the bottom.(4)Studing the maximum horizontal displacement of building pile foundation and the plastic zone of slope under earthquake,different seismic optimization schemes are proposed for two conditions.In the case of slope before building,adding sleeve at the side of pile foundation can reduce the maximum horizontal displacement of building pile foundation.In the case of building before the slope,increasing the initial prestress of anchor cable can achieve a certain seismic effect,which reduces the plastic zone of the slope and the maximum horizontal displacement of the building pile foundation.