受损无压管道诱发砂土地基内部侵蚀及失稳机制研究

Ground failure induced by damaged non-pressure pipes is posing threat to the urban safety. The mechanism of ground failure due to defective pipes is different from that induced by external loads. Defects on underground pipes may alter the boundary condition of groundwater flow, which will result in a high hydraulic gradient and seepage concentration adjacent the defect. Therefore, fine particles in sandy soils will be lost and migrated through coarse particles by internal erosion, which will lead to the reduction of soil mechanical character. Finally, the ground failure may occur as the expansion of internal erosion. Generally, the mechanism of internal erosion, evolution of sandy soil mechanical behavior and mechanism of ground failure is the key issue in this project. This project will be initiated by investigating the mechanism of sand soil internal erosion, which will be conducted using the soil column and CT scanning test. The mechanism of sand soil internal erosion can be studied from both macro and micro scales. Through a coupled discrete element method, effects of stress state, hydraulic condition, and soil particle size distribution will be quantitatively evaluated, and a mathematical model will be developed to predict the variation of soil mechanical properties. After introducing this proposed mathematical model, the numerical code, FLAC, will be improved to predict the occurrence of ground failure, which will be verified by centrifuge physical modeling tests. Therefore, the threshold leading to the ground failure can be determined through numerical and physical modeling studies. This project may guide the future non-pressure pipe engineering, which may also provide an effective approach to avoid the ground failure.

受损无压管道诱发的砂土地基失稳塌陷灾害已对城市安全构成了严重威胁。不同于传统地基失稳机制，这类灾害是由于管道损伤导致地下水运移边界条件改变，周边土体内形成集中渗流，造成地基土内部侵蚀及力学特性演变并最终导致地基失稳。目前由于对这一机制缺乏深入认识，受损无压管道诱发的地基失稳塌陷灾害管理仍处于被动应急状态。为此本项目从砂土内部侵蚀机制出发，结合单元体试验和CT扫描技术，揭示砂土内部侵蚀的宏观表征及微观机理；利用流固耦合离散元数值模型，揭示土体不同应力状态、水力条件、颗粒级配下的地基土力学特性演变规律，建立地基土力学特性表征模型；在此基础上，开展有限差分程序二次开发，与离心机模型试验相互验证，揭示砂土地基内部侵蚀作用下的失稳机制，建立失稳触发分析方法，确定无压管道损伤条件下的地基失稳触发阈值。研究成果将为解决受损无压管道引起的灾害防控提供理论依据和技术支持。

受损无压管道诱发的砂土地基失稳塌陷灾害已对城市安全构成了严重威胁。不同于传统地基失稳机制，这类灾害是由于管道损伤导致地下水运移边界条件改变，周边土体内形成集中渗流，造成地基土内部侵蚀及力学特性演变并最终导致地基失稳。本项目从砂土内部侵蚀机制出发，结合离散元数值模拟和CT扫描实验技术，揭示砂土内部侵蚀的宏观表征及微观机理，建立间断级配砂土内部侵蚀模型、考虑粒径及渗流速度影响的土体内细颗粒迁移-堵塞相图及颗粒通过管道破损收缩断面桥接模型；利用流固耦合离散元数值模型，揭示土体不同应力状态、水力条件、颗粒级配下的地基土力学特性演变规律；开展了不同破损位置的受损管道诱发地基失稳模型试验，揭示砂土地基内部侵蚀作用下的失稳机制，建立失稳触发分析方法，建成了管道受损诱发地基失稳的离心模型试验装置，并完成了装置地面调试和预实验。研究成果将为解决受损无压管道引起的灾害防控提供理论依据和技术支持。