Study On Interaction Mechanism Between Micro-Piles And Landslides And Soil-Arch Effect

In recent years,micro-piles have been gradually applied to control landslide disaster.This is due to the advantages of simple construction,various arrangements of pile,strong emergency response ability and strong site adaptability.Many scholars have systematically studied the interaction mechanism,deformation and failure characteristics of micro-piles and landslides under static loads,but few scholars have studied the seismic performance of micro-piles.Based on the project of National Natural Science Foundation "Research on Dynamic Interaction between micro-piles and Landslides",shaking table test of micro-piles supporting accumulative landslides are carried out.The dynamic interaction mechanism,pile-soil deformation characteristics and anti-seismic characteristics of micro-piles are analyzed by the test and numerical simulation.On the basis,the numerical simulation of micro-piles soil-arch effect in the prevention and control of accumulative landslides are carried out.In this paper,a more suitable pile spacing is proposed.The main research work are as follows.(1)Based on the prototype slope and the equipment parameters of shaking table,the geometric similarity scale 1:8 is determined.According to the similarity principle,the derivative's physical similarity ratio is deduced to guide the material parameter ratio of model test.On the basis,the test scheme of interaction between micro-piles and accumulation landslide are designed.Shaking table test was carried out in comparison with static test.(2)In the accumulation landslide,the final deformation and failure of micro-piles are bending failure under static and dynamic loads.And the pile body and reinforcing cage have greater plastic deformation after failure.Compared with homogeneous soil,micro-piles have no deformation in the embedded section.The lowest bending failure point is at the sliding surface.Pressure cracks occur in front of piles and tension cracks occur behind piles.The highest bending failure point of each row of piles are in the range of 3 to 5 pile diameters.Tensile cracks occur in front of piles and compressive cracks occur behind piles.The soil behind the pile has void near the sliding surface.And the closer pile was to the foot of the slope,the higher void height would be.(3)Based on the test and numerical simulation,the thrust partition coefficients of three rows of piles are analyzed.It is found that the thrust partition coefficients of each row of piles under dynamic loading were different from those under static conditions.Static test,back row piles: middle row piles: front row piles = 0.40:0.37:0.23.Static numerical simulation,back row piles: middle row piles: front row piles = 0.40:0.33:0.27.Considering comprehensively,it is recommended that the thrust partition coefficient obtained from the test be selected in the design of actual micro-piles.Seismic action,back row piles: middle row piles: front row piles = 0.51:0.17:0.32.Seismic numerical simulation,back row piles: middle row piles: front row piles = 0.42:0.32:0.26.Considering comprehensively,it is recommended that the thrust partition coefficient obtained by simulation be selected in the actual seismic design of micro-piles.(4)Under earthquake action,the higher the landslide elevation is,the larger the magnification factor is.The soil pressure,bending moment and displacement of micro-piles have obvious time-history effect.With the fluctuation of seismic wave,the peak acceleration is the main factor of landslide failure and instability.(5)On the basis of comparison between the test and the simulation,soil-arch effect of three pile spacing,pile diameter ratio L/D=3,L/D=5 and L/D=7,is analyzed.The soil-arch effect was the strongest and the supporting effect was the best when the pile diameter ratio is 5 times.On the basis,the results show that optimum pile diameter ratio is L/D=5.5 in static loading.And optimum pile diameter ratio is L/D=5.9 in seismic loading.