动态承压水头作用下深基坑突涌演变和破坏机理

Accompanied by the recent urbanization in China, it is common for geotechnical projects in coastal and riparian regions (such as construction of high-rise building, development of underground space, river/sea-crossing bridge and tunnel) to encounter situations that the confined aquifer is penetrated or overlain by the deep excavation. In such situations, the dynamic water head of the confined aquifer, due to influence of wave or tide, may lead to substantial negative effects on the deformation, instability and environment of the excavation. Particularly, initiation and mechanism of piping is the key issue to the safety and performance of coastal and riparian deep excavation..The present project,basing on theory of consolidation and seepage, establishing idealized model considering unloading effect on the base of excavation and fluctuated water head in confined aquifer, includes laboratory model test, element tests on base soil, and nonlinear numerical analysis and analytical analysis, in order to reveal engineering properties of base soft clay, initiation of piping and corresponding failure pattern and mechanism. Based a deep excavation case, design approach to estimate the hydraulic uplift stability of the excavation subjected to fluctuated water head in confined aquifer will be recommended. It is of great theoretical and practical importance to extend design and calculation theory of excavation retaining structure under complex conditions, and to provide scientific guidelines for coastal and riparian retaining structure design and construction.

随着我国城市化进程的推进，在滨海或沿江地区地下空间、跨海大桥、越江（海底）隧道的建设过程中，常面临深基坑穿越承压含水层或者坑底隔水层以下存在承压层的情况，且含水层受海洋或河流潮波的影响，承压水位呈动态变化,由此引起的基坑变形、失稳及环境影响问题十分突出，其中在动态承压水头作用下的深基坑突涌演变和破坏机理是需解决的关键科学问题。.本项目从土体固结渗流理论出发，建立动态承压水头作用的基坑分析模型，开展相应的室内物理模型试验、坑底弱透水层的土单元体试验、非线性数值分析与解析研究，深入揭示基坑开挖卸荷后经受动态承压水作用的坑底软黏土的工程特性、基坑突涌失稳的破坏模式及其诱发、演变和破坏机理，结合深基坑工程实例分析，提出动态承压水作用的深基坑抗突涌稳定设计方法。无疑将极大地丰富和发展复杂环境下的基坑支护结构设计计算理论，为滨海、沿江深基坑支护的设计和施工提供科学依据，具有重要的科学意义和应用价值。

随着我国城市化进程的推进，在滨海或沿江地区地下空间、跨海大桥、越江（海底）隧道的建设过程中，常面临深基坑穿越承压含水层或者坑底隔水层以下存在承压层的情况，且含水层受海洋或河流潮波的影响，承压水位呈动态变化,由此引起的基坑变形、失稳及环境影响问题十分突出，其中在动态承压水头作用下的深基坑突涌演变和破坏机理是需解决的关键科学问题。. 项目研制了模拟承压水变化的一维圆筒土体渗流试验装置，通过室内试验研究了钱塘江黏质粉土在波动承压水作用下的孔压变化规律，探讨了动态承压水作用下弱透水层突涌触发、演变和破坏机制。基于深大基坑坑底弱透水层的一维越流模型，推导得到了承压水头变化引起的坑底弱透水层中的超静孔隙水压力和出逸比降的解析表达式，进一步考虑弱透水土体的渗透和压缩非线性、非达西流、土体大应变和双层地基等复杂因素，开展了复杂条件下动态承压水引发的基坑底部弱透水层非线性渗流和突涌规律的解析和有限差分法研究。建立了承压水作用的三维基坑数值分析模型，研究了坑底弱透水层中存在渗透薄弱面和局部深坑时波动承压水作用下弱透水层渗流稳定性问题。研究发现当承压水位波动时，土体达到突涌破坏时的最高水头高于恒定水头条件下的破坏水头，表明承压水位变化在坑底土层中传播有滞后性；在动态承压水变化周期长、平均水位高、波动幅值大的情况下若忽略土体非线性进行基坑突涌分析将偏不安全；当坑底存在渗透薄弱面或局部深坑时，弱透水层中的最大出逸比降明显增加，基坑突涌风险显著增大。. 项目深入揭示了经受动态承压水作用的基坑坑底弱透水土体的渗流特性、基坑突涌失稳诱发、演变和破坏机理，丰富和发展了复杂环境下的基坑支护结构设计分析理论，为滨海、沿江深基坑支护的设计和施工提供科学依据，具有较强的科学意义和应用价值。