盾构竖井垂直顶管顶升力模型试验及离散元分析

Model tests and discrete element analysis on jacking force of shield shaft vertical pipe jacking

研制室内试验装置,开展盾构竖井垂直顶升施工的模型试验,分析顶管上覆土层的破坏机制、形态,揭示顶升力计算的土层合理破坏范围。借助离散元模拟顶管顶升过程,与试验结果进行对比分析,并探讨顶升力主要的影响因素,提出顶升力的估算方法。研究结果表明:在顶管顶升阶段,上覆土经历挤压剪切—局部破坏开裂与延伸—破坏面贯通—裂隙发展—形成土柱—土层重分布—填充裂隙的过程。上覆土破坏面具有典型的非线性特征,呈三次函数分布,现有研究假定破坏面沿特定倾角线性分布不合理。破坏面贯通前,顶升力显著增大,顶升至h/16(h为顶升高度)时出现最大值,随后土层剪切破坏,顶升力迅速减小并逐渐趋于稳定。实际上覆土层破坏范围比经验取值的大,试验顶升力较经验计算值大46.23%~83.05%,可见按经验法计算顶升力明显偏小。离散元分析结果表征了顶管上覆土层的破坏形态,破坏范围、顶升力与试验结果相吻合,说明利用离散元模拟顶管垂直顶升可行。不同因素对顶升力的影响程度由大到小依次为上覆土层深度、黏聚力、摩擦角,顶升力与上覆土层深度近似满足二次抛物线关系,与黏聚力及摩擦角则呈同向线性关系。基于上覆土层的破坏形态和顶升力主要因素的影响特征,提出顶升力2种估算思路,并由实例验证其可行性。

The laboratory model test device was developed to carry out the model test of vertical jacking construction. The failure mechanism of the overlying soil and failure range for calculating jacking force were analyzed. The pipe jacking process was simulated by discrete element, whose results were compared with test results. The main influencing factors of jacking force were discussed and the estimation method of jacking force was proposed. The results show that in the jacking stage, the overlying soil undergoes a process of compressive shear, local failure, crack and extension, failure surface connection, crack development, soil column formation,redistribution, and crack filling. The failure surface of the overlying soil has typical nonlinear characteristics and presents cubic function distribution, which indicates that the linear distribution of failure surface along a certain angle is unreasonable. Before failure surface connection, the jacking force increases obviously and the maximum appeares when jacking is to h/16. And then the failure surface is formed, the jacking force decreases and becomes stable gradually. The failure range of overlying soil is significantly larger than the empirical value, and the experimental jacking force is 46.23%-83.05% larger than the empirical results, indicating that the jacking force calculated by experience is significantly smaller. The discrete element analysis results represent the failure mode of the overlying soil, and the failure range as well as jacking force are consistent with the test results. Using discrete element to simulate the vertical jacking is feasible. The influence degree of different factors on the jacking force is overlying soil depth, cohesion force and friction angle. The relationship between the jacking force and overlying soil depth is quadratic parabola, and that between the jacking force and cohesion force, friction angle is linear. Based on the failure mode of the overlying soil and the influence characteristics of the main factors on jacking force, the two estimation methods of jacking force are proposed and verified by example.