软土工程局部破坏引发连续破坏机理及连续破坏控制理论研究

There are more and more deep excavation，underground tunnel, and soft ground improvement projects in or on soft ground to be constructed with the development of metro, high-rise building and skyscraper, highway and railway, underground transportation hub in soft ground area. The construction of these projects inevitably changes the stress field and seepage field of soil and unground water in the surroundings. When the change of stress field and stress field are beyond certain extent, or even accompanied with soil erosion, water and soil loss due to leakage in underground engineering and deep excavation, local failure of underground structure or soil can happen and may finally lead to progressive failure. The progressive failure of deep excavation，underground tunnel, and soft ground improvement projects can caused more severe loss and produce more significant impact on surrounding environment and more extensive social impact than that of a building or a bridge. Since deep excavation，underground tunnel, and embankment supported soft ground improved with piles are composed of soil, underground water and structure, this makes the interaction and failure mechanism of soil-underground water-structures more complicated. Therefore, the progressive failure problem of soft soil engineering of geotechnical engineering and underground engineering is raised. The interaction of soil-water-structure and the progressive mechanism of soft ground engineering such as deep excavation，underground tunnel, and soft ground improvement projects during the whole failure evolution process starting with local failure, then the evolution and propagation of failure, until the end of progressive failure. The quantitative indexes and method to evaluate the possibility of a soft soil engineering being subjected to progressive failure are to be proposed. Finally, the anti-progressive failure theory and corresponding design method of important engineering projects in or on soft soil are to be suggested.

软土地区的城市交通枢纽、地下铁道、超高层建筑、高速公路与铁路等的建设涉及到大量深基坑、地下隧道、软土路基处理等。这些工程的建设不同程度地改变了工程周边环境场地中土体应力场和渗流场，当应力场、渗流场异常或甚至出现水土流失时可造成土体、土中结构物的局部破坏，并由局部破坏甚至引发大范围连续破坏，有些连续破坏的损失、环境与社会影响甚至可比建筑物、桥梁等的连续破坏更严重，由软弱土体-地下水-土中结构物组成的岩土与地下工程的共同作用及破坏机理有时可能更为复杂。提出了岩土与地下工程的连续破坏问题，拟针以软土富水地层中的大型复杂深基坑工程、地下隧道和软土中复合地基支承路堤为代表的软土工程，开展局部破坏发生、发展及最终发展为连续破坏的全过程中土体-地下水-结构体的复杂相互作用和连续破坏机理研究，提出软土工程的连续破坏性能评价指标体系和评价方法，系统建立重要软土工程的防连续破坏理论和基于防连续破坏的设计方法。

软土地区的城市交通枢纽、地下铁道、高速公路与铁路的建设涉及到大量深基坑、地下隧道和软土路基处理等。这些人类建设活动不同程度地改变了周边环境场地中的土体应力场、地下水渗流场。当应力场、渗流场异常或出现水土流失时，可造成土中结构物的局部破坏，甚至还可能引发大范围的连续破坏。本项目结合案例调研、数值模拟、模型试验和理论分析等手段，针对软土工程连续破坏问题开展了系统研究，构建了基于防连续破坏设计的理论框架。针对基坑局部破坏引发的连续破坏沿基坑深度、宽度、长度方向的发展问题，揭示了悬臂式排桩支护、内撑式和桩锚式支护等典型基坑支护体系的连续破坏发展机理及自然终止机理，提出了综合冗余度因子、荷载传递系数等防连续破坏韧性量化评价指标和相应评价方法，建立了基于三个水准（防局部破坏、防局部破坏发展为连续破坏、预控连续破坏发展范围）的基坑工程防连续破坏韧性设计理论与设计方法。针对盾构隧道由局部渗漏引起土层流失进而导致隧道结构产生变形、损伤的情况，开展介观至宏观尺度的模型试验，研究了隧道周围土层的流失规律，分析了隧道结构的变形和损伤机理。在此基础上，数值模拟再现了盾构隧道因局部破坏导致大规模水土流失情况下的连续破坏发展过程，揭示了不同埋深下盾构隧道连续破坏触发及传递机理，提出了量化评价指标和评价方法。同时，基于三个水准设防的盾构隧道防连续破坏研究，以提升隧道整体安全性能为目标，优化了隧道结构设计方法与理论。针对复合地基支承路堤的连续破坏问题，揭示了基于不同破坏模式下刚性桩支承路堤沿宽度方向和长度方向的连续破坏诱发及传递机理，分析了桩帽、桩间距和桩体刚度等因素对连续破坏扩展和演化机理的影响，建立了三个水准的复合地基支承路堤防连续破坏的改变加固体刚度/置换率防止初始破坏、非等强和非等长设计的破坏中止以及增设加筋体提升鲁棒性的控制理论与方法，提出了复合地基支承路堤防连续破坏性能的量化评价指标和评价方法。