大面积基坑多级支护理论与工程应用实践

大面积基坑采用常规钢筋混凝土水平支撑时，其水平支撑造价高、施工工期长，且拆除后会产生大量固体废弃物。发展了系统的大面积基坑多级支护方法，对其破坏机制和设计方法开展了研究。当围护结构内侧的反压土宽度不足够大时，采用多级支护取代宽度较大的反压土，可有效控制基坑围护结构变形。当两级支护之间宽度较小时，多级支护的工作机制和破坏机制近似于异形重力式挡土墙，可产生整体式破坏（包括整体倾覆、整体失稳等）；而随着多级支护之间的宽度增大，土体的破坏面可进入多级支护的围护桩之间的土体，并使多级支护桩的破坏产生相互关联的影响；当多级支护的宽度足够大时，多级支护可产生各自独立的破坏。工程应用实践表明，条件适当时，多级无支撑支护可取得较好的经济效益并节省地下工程工期。

Theory of multi-bench retaining for large area foundation pit and its engineering application

When the horizontal reinforced concrete struts are used in retained foundation pit of large area，the cost of horizontal reinforced concrete struts will be very high and need long construction period. Moreover, large amount of solid waste will be produced after the struts been demolished. Therefore, the multi-bench retaining method is developed and was used in large area foundation pit projects. The failure mechanism of multi-bench retained foundation pit is investigated and design method is studied. The multi-bench retaining structure can fail as overall stability failure or overall overturning failure like a gravity retaining wall when the width of the bench is small. The slip surface can extend into the soil between retaining pile of different benches with the increase of the width of the bench, this leads to the mutual-effect between the multi-bench retaining piles. Separate failure can occur to the multi-bench retaining pile when the width of the bench is big enough. The application of multi-bench retaining method shows that multi-bench retained foundation pit with the use of horizontal reinforced concrete struts can be highly cost-effective and construction period of underground structure can be significantly reduced.