黏性隔水层基坑突涌机制的离心模型试验

CENTRIFUGAL MODEL TESTS ON HYDRAULIC HEAVE MECHANISM OF EXCAVATION IN COHESIVE SOIL WITH CONFINED WATER

针对承压水作用下基坑底隔水层为黏性土体的情况,设计突涌离心模型试验,分析不同开挖深度和水位作用下围护墙的弯矩、水平位移与稳定性,观测坑底土体隆起和突涌破坏状态。试验结果表明:随着承压水头的升高或开挖深度的增加,土体隆起变形的曲率变大并在坑底中央逐渐产生裂隙破坏;墙体被动侧土体抗力逐渐减小,围护墙弯矩和水平位移逐渐变大;围护墙后土体内形成竖向裂纹,基坑发生踢脚破坏。考虑土体强度的基坑抗突涌稳定性分析,宜将土体黏聚力折减来反映土体与围护结构接触缺陷、隔水层裂隙发育以及受到地下水软化等不利因素的影响。

Centrifugal model tests were designed to simulate hydraulic heave in low permeable cohesive soil under the action of confined water.The bending moment,horizontal displacement and stability of retaining wall at different excavation depths and confined water levels were analyzed.In addition,the heave deformation and hydraulic failure at excavation bottom were observed.Test results indicate that：excavation bottom uplift and deformation curvature increase with increases of confined water pressure and excavation depth;and cohesive soil progressive fracture appears in the center of foundation pit.At passive side of retaining wall,the resistance of soil gradually decreases;while the bending moment and horizontal displacement of retaining wall become greater.Eventually,vertical crack appears in the soil behind retaining wall;and test foundation pit collapses because of hydraulic heave.When analyzing hydraulic heave stability of foundation pit considering the shear strength of cohesive soil,cohesion c should be multiplied by a reduction factor to take some adverse factors into account,such as interface defect of soil-retaining structure,progressive hydraulic fracture and cohesive soil softening induced by groundwater,etc..