Analysis Of Isolated Effect Of Micro Piles And Stress Release Hole For Construction Displacement Induced By Jacked Pipe Pile Group

Based on the engineering background of the Qufudong Station of the Beijing-Shanghai high-speed railway,which introducd the new-bulit Lunan highspeed railway,combined with field tests and Coupled Eulerian-Lagrange(CEL)numerical analysis,when the micro grouting steel pipe pile or stress release holes were used as isolation measures,the distribution law of the displacement of soil caused by the jacked pipe single pile and group pile was studied to analyze their displacement isolation effect.The main work and conclusions are as follows:(1)Based on the field measured data of the disturbance displacement of adjacent soil during the micro-pile forming process in the Ⅲ and V test areas,the effects of the forming process of different rows of micro-piles(5 rows in the Ⅲarea and 8 rows in the V area)on the displacement on surface and the horizontal displacement of deep soil were analyzed.The results show that the disturbance displacement of adjacent soil during the micro-pile forming process is not more than 1.4mm.(2)When the micro piles were used as isolation piles,the monitoring data of the disturbance displacement of the adjacent soil by the jacked pipe pile group piles in the Ⅲ and V test zones was analyzed,the distribution laws of the displacement on surface and the horizontal displacement of deep soil were revealed,and the displacement isolation effects of micro piles with different rows were compared.The results show that the lateral horizontal displacement of deep soil under the isolation condition of micro-piles decreases gradually along the depth.With the number of rows of micro-piles increase from 5 rows to 8 rows,the reduction of the horizontal displacement of the soil in the protection area is no more than 9.0%.(3)A CEL finite element model of the jacked pipe pile group in the Ⅲ test zone was established.By comparing the calculated results with the measured results,the rationality of the numerical analysis modeling method and calculation parameters is verified.On this basis,based on the variable analysis method,CEL models of the jacked pipe pile group under different isolation conditions were established to explore the influence of the number of rows,length and layout of micro-piles on the construction disturbance displacement of the jacked pipe pile group.The results show that when micro piles are increased from 1 row,3 rows to 5 rows,their lateral horizontal displacement on the surface compared with no isolation piles is reduced by 15.4%,33.3% and 43.2%,respectively,and their maximum horizontal displacement of the deep soil is reduced by 22.8%,44.6%and 63.1%.In the same replacement rate,the displacement isolation effect of the micro-piles in torx arrangement is stronger than that of in parallel arrangement.(4)A CEL finite element model of the jacked pipe single pile under the isolation condition of a single row micro-pile was established to analyze the development law of the soil displacement under different pile pressing depths.The results show that the maximum lateral horizontal displacement of deep soil in adjacent sites(<16D)is obtained near the pile tip under different pile pressing depths.The surface vertical displacement is in settlement within about 1D around the jacked pipe pile,and uplift outside.(5)According to the literature engineering background,a CEL finite element model of the jacked pipe single pile under the isolation condition of pre-drilled hole + stress release hole was established.The variation law of the horizontal displacement of deep soil at 1.5m and 5m from the center of the jacked pipe pile along the depth obtained by calculation are basically the same as that measured,and the error of their maximum displacement is within 12.2%,which verifies the rationality of the CEL finite element model modeling method of the jacked pipe pile under the isolation condition of stress relief holes.(6)Referring to the engineering conditions of the Ⅲ test zone,CEL finite element models of the jacked pipe single pile under the isolation condition of a single row of stress release holes were established to explore the development laws of the soil displacement in adjacent sites with different diameters(300mm,400 mm and 500mm).The results show that with the diameter of stress release holes increases from 300 mm to 500 mm,the displacement isolation effect increases gradually,and the maximum lateral horizontal displacement of deep soil at 2m away from the jacked pipe single pile decreases by 34.3%;The displacement isolation effect of a single row of stress relief holes(hole diameter300mm)is stronger than that of a single row of micro piles(pile diameter 150mm).(7)CEL finite element models of the jacked pipe pile group under different isolation conditions of stress release holes were established to compare and analyze the influence laws of the number of rows,depth and layout of stress release holes on the construction disturbance displacement of the jacked pipe pile group.The results show that the displacement isolation effect is gradually enhanced with the increase of stress release holes from one row to three rows.When the replacement rate is equal,the displacement isolation effect of stress release holes in torx arrangement is stronger than that of in parallel arrangement.