Research On Structure Design Of Micro Pile Group Based On 3D Numerical Simulation

The bearing capacity of single micro pile is low under horizontal force,so it is necessary to lay micro pile group to control landslide.At present,the research on antiskid micro pile mainly focuses on pile force,pile internal force and pile deformation,etc.Therefore,it is of great practical application value to study the influence of pile spacing,pile row spacing,pile length,pile section size and formation physical and mechanical parameters of embedded section on the structural design of micro pile group.Based on the existing micro-pile reinforcement theory and physical model test,a threedimensional numerical model is established by FLAC 3D.By comparing and analyzing the pile deformation,soil stress distribution and internal force change of the numerical simulation test of micro pile group with different pile spacing,different pile row spacing,different pile length,different pile section size and different embedded strata,the method of determining the design parameters of micro pile group structure is proposed.The research contents and achievements of this paper are as follows:(1)The physical model test of three rows of connected micro pile group shows that the horizontal displacement of pile top gradually increases with the increase of load.Due to the constraint of pile top connected structure,the final displacement values of three rows of piles are close to each other.The soil stress behind the load section reaches its maximum value above the sliding surface,while the soil stress in front of the anchorage section reaches its maximum value below the sliding surface.The bending moment value decreases from the first row to the third row.(2)By comparing the physical model test with the corresponding numerical simulation test,it is concluded that the two test laws are consistent.Micro-pile bending deformation along the sliding direction;the maximum value of the soil stress after the pile is near the middle of the load section,the maximum soil stress before the pile is near the sliding surface,indicating that the soil at this position bears more loads.Pile bending moment is inverted "S" type.Therefore,the parameters of the physical model test are directly used as the parameters of the numerical simulation test,which is reliable and can carry out multiple groups of numerical simulation conditions.(3)The influence of different pile spacing on the skid resistance of micro pile group was analyzed.The numerical simulation tests of micro pile group with pile spacing of 3 times pile diameter,4 times pile diameter and 5 times pile diameter were selected,and the results showed that the micro pile group with pile spacing of 4 times pile diameter had greater flexural ability,smaller pile displacement and more uniform distribution of soil stress before and after the pile.Therefore,when arranging micro pile group,the reasonable pile spacing should be 4 times pile diameter.(4)The influence of different pile row spacing on skid resistance of micro pile group was analyzed.Numerical simulation tests of micro pile group with pile row spacing of 3 times pile diameter,4 times pile diameter and 5 times pile diameter were selected.It was concluded that the micro pile group with pile row spacing of 4 times pile diameter had greater flexural ability,smaller pile displacement and more uniform distribution of soil stress before and after the pile.(5)The influence of different pile lengths on the sliding resistance of micro-pile group was analyzed.Numerical simulation tests of micro-pile group with pile lengths of 1.3m,1.5m and 1.8m were selected.It was concluded that with the increase of pile length,pile displacement decreases,pile load increases,and the greater the landslide thrust borne by soil between piles,the greater the bending ability of pile.Therefore,the length of the embedded section of micro-piles should not be less than 1/2 of the total pile length when micro-piles are laid.(6)Analyze the influence of different pile section sizes on the sliding resistance of micro-pile group,and select the numerical simulation test of micro-pile group with pile diameters of 0.05 m,0.075 m and 0.10 m.It is concluded that,with the increase of pile diameter,pile displacement decreases,pile load increases,landslide thrust carried by soil in front of the pile increases,and pile flexural effect increases.Therefore,micropiles with smaller diameters can be selected for the same anti-sliding ability,and micropiles with larger diameters can be selected for higher deformation control.(7)The influence of different embedded-section strata on the sliding resistance of micro-pile group was analyzed.The numerical simulation test of micro-pile group in which the embedded-section strata are homogeneous soil,soil and rock mass and rock mass was selected showed that the deeper the embedded-section strata are,the smaller the pile displacement is,and the soil stress before and after the pile expands obviously in the rock mass of embedded-section strata.When the pile is embedded in a certain depth,the pile bending moment is very small(close to "0").Therefore,when micropile group is arranged in landslide and micro-pile needs to be embedded into rock mass,the pile diameter of micro-pile should be increased and the length of embedded section can be reduced appropriately.