隔离桩对基坑外既有隧道变形控制的优化分析

OPTIMIZATION ANALYSIS OF EFFICIENCY OF ISOLATION PILES IN CONTROLLING THE DEFORMATION OF EXISTING TUNNELS ADJACENT TO DEEP EXCAVATION

隔离桩对土体深层位移的影响及用于控制一定埋深的邻近既有隧道的作用机制尚缺乏研究。针对天津市采用隔离桩保护邻近既有隧道的某深大基坑工程,实测地下连续墙、坑外土体、隔离桩及隧道的变形。后在工程实测基础上,采用考虑土体小应变特性的有限元方法,对隔离桩的作用机制进行参数分析,研究隔离桩对土体深层位移及隧道位移的控制机制。研究结果表明,隔离桩在控制坑外土体、隧道水平位移时同时存在阻隔作用和牵引作用,当牵引作用较大时,隔离桩反而可加大一定深度范围内土体及该范围内隧道的水平位移;由此提出埋入式隔离桩的形式,可减小其牵引作用从而主要发挥其隔离作用,并减小隧道水平位移。同等条件下,隔离桩距隧道较近时隔离效果更好。

The mechanism of effects for isolation piles on reducing displacements of soil and tunnel below the ground surface needed to be studied. Field measurements were carried out in a deep excavation project in Tianjin,which adopted the isolation piles to protect the adjacent existing tunnel. The deformations of the diaphragm wall,soil outside the excavation,isolation piles and the tunnel were obtained and analyzed. Based on the measured data,a parametric study of isolation piles using finite element method considering the small strain of soil was conducted to investigate the horizontal displacements of the tunnel and the soil below the ground surface adjacent to a deep excavation. It was shown that isolation piles had both effects of isolation and drag on the tunnel adjacent to the deep excavation. The deformation of adjacent tunnel from deep excavation can be increased when the drag effect was more remarkable. The buried isolation pile could be used to minimize the effect of drag and the horizontal displacement of tunnel. Moreover,the isolation piles had higher efficiency in reducing the tunnel displacement when the piles were located closer to the tunnel.