邻近地层损失对地下挡土结构土压力与地表沉降影响试验研究

Experimental investigations on influences of ground loss on earth pressure and settlement of adjecent underground retaining structures

城市浅层空间隧道往往从一侧或两侧地下挡土结构物之间穿过,多数情况下会引起地层损失。目前城市地下开挖引起塌陷事故呈现逐年增多的趋势,当地层损失产生后,周边已建或在建基坑挡土结构的土压力和地层沉降发展规律是决定是否需要进行加固或处理的依据。为了获取地层损失的扰动影响规律,开发了模型试验装置与钢棒相似土技术,采用活动门下沉模拟地下开挖引起的地层损失,采用挡墙平移模拟基坑开挖。分别考虑活动门深度与宽度比、活动门位置深度与距离比、活动门位置深度与侧限宽度比,开展了15组二维模型试验。利用挡土板上的18块悬臂式载荷计测得挡土结构土压力,采用粒子图像测速技术获取表面沉降曲线。结果表明:地层损失会使邻近基坑挡墙上部土压力增加,下部土压力减小;地层损失发生后,邻近的新建基坑如继续进行开挖施工,由于土体受到了充分的扰动,挡土结构底部不会出现土压力减小的箱槽效应,挡墙平移达到主动极限状态时的土压力分布与库仑主动土压力较为吻合;邻近地下开挖引起地层损失与挡墙平移的叠加效应影响下,地表沉降最大值和曲线曲率随活动门宽度增加而增加,随活动门距离和侧限宽度减小而增加。由于采用钢棒相似土,所获得的研究成果主要反映砂土地层的土压力与变形特性。

Underground excavations often pass through underground retaining structures on one side or between the structures. In most cases, ground loss will be caused. At present, there are more and more collapses caused by excavation. When the ground loss occurs, the development of earth pressure and ground settlement is the decision basis for structural reinforcement or treatment. To obtain the preliminary rules of disturbance influences of the ground loss, the model test setup and the steel rod analogical soil technology are developed. A trapdoor is used to simulate the stratum loss caused by underground excavation and collapse, and the foundation pit excavation is simplified as the translation of the retaining wall. Considering the ratios of trapdoor depth to width, trapdoor depth to distance and trapdoor depth to side limit width, 15 groups of two-dimensional model tests are carried out. The earth pressure of retaining structures is measured by 18 cantilevered loaders on the retaining plate, and the surface settlement curve is obtained by the particle image velocimetry. The results show that ground loss increases the earth pressure at the upper part of the retaining wall and decreases the earth pressure at the lower part of the retaining wall. After the occurrence of the ground loss, if the adjacent foundation pit continues being excavated, due to the disturbance of the soil, there is no "bin effect" of the decrease of the earth pressure at the bottom of the retaining structures, and the earth pressure distribution when the retaining wall translation reaches the active limit state is in good agreement with the Coulomb’s active earth pressure. Under the influences of the superposition effect of the translation of the retaining wall after the ground loss caused by the adjacent underground excavation, the maximum value of surface settlement and the curvature of curve increase with the increase of trapdoor width, and increase with the decrease of trapdoor distance and side limit width. Due to the use of steel rod analogical soil, the test results mainly reflect the earth pressure and deformation characteristics of the sandy soil.