深基坑复合土钉支护模型试验研究

MODELING STUDY ON COMPOSITE SOIL NAILING FOR DEEP EXCAVATION

复合土钉支护是在土钉支护基础上发展起来的、用于深基坑支护或提高边坡稳定性的一种新技术,为深入了解其工作性能和作用原理,促进该项技术快速发展,进行了室内模型试验研究。深基坑模型按照“相似模型的几何长度与变形时间成反比”的相似法则设计,相似比为1∶10。在试验中,模拟深基坑开挖与支护的实际步骤,分步开挖与支护。进行了3组模型试验,即复合土钉支护、普通土钉支护和无支护边坡,以便于分析比较。借助位移传感器测量深基坑地表沉降、基底隆起和坡面水平位移,通过布设在模型箱透明玻璃侧面内的观测点,测量边坡内土体的位移。试验结果表明:(1) 由于土钉与水泥土搅拌桩的共同作用,复合土钉支护的基坑变形与普通土钉支护和无支护的基坑相比,具有不同的分布形态,并且复合土钉支护的基坑变形值最小,无支护基坑变形值最大;(2) 由于土钉与水泥土搅拌桩的协同工作,使得更多的土体参与支护作用,从而分散了土体内部的应力,有效地控制了基坑变形,提高了基坑的稳定性。

The composite soil nailing is a new technique developed from soil nailing for retaining excavation or improving stability of existing slope. A modeling test of the composite soil nailing is carried out in laboratory to study its behaviors and working mechanism and hence facilitate its development. The retaining structures are modeled according to the similarity rule in which the geometric length of the structure is in inverse proportion to the duration of the structure deformation and the adopted similarity ratio was 1:10. The sequential excavation and retaining are conducted during the experiment to simulate the actual construction procedures in situ. Three cases, including composite soil nailing, soil nailing and excavation without any retaining, are executed in the modeling test to compare and analyze their behaviors. Ground subsidence, rebound deformation and horizontal deflection are measured by means of displacement transducers, and the displacements inside the excavated slope are monitored by a network of surface movement markers installed inside the transparent glass side of the modeling device. The measured results show that (1) the distribution of deformations of composite soil nailing is different from those of general soil nailing and excavation without any retaining because of the cooperation of the nails and the soil-cement piles, and among the deformations, those of composite soil nailing are the smallest and those of excavation without any retaining are the largest, (2) the cooperation of the nail and the soil-cement piles in the composite soil nailing causes more subsoil participating in retaining action than in the soil nailing due to the uniform stress distribution near the slope. The deformation induced by excavation is controlled effectively and the stability of the excavated slope is improved.