既有渣土堆载深大基坑边坡稳定性与支护技术研究

为获得深大基坑既有渣土堆载条件下的边坡失稳机制，提出联合支护技术，以重庆地铁项目放坡开挖深大基坑工程为依托，依据强度折减理论，综合采用数值模拟与现场实测手段开展研究。主要结论如下： 1）渣土堆载侧边坡潜在破坏类型为剪切滑移破坏，最大剪切应变率沿坡脚向坡顶逐渐形成、延伸并呈“带状”贯通，是基坑发生滑移失稳破坏的内在根源； 2）土层采用“大坡率放坡+铺网喷护”，土层坡比为1∶1.75，钢筋网片+喷射混凝土面； 3）岩层采用“小坡率放坡+锚网喷”，岩层坡比为1∶0.75，锚杆+钢筋网片+喷射混凝土面。数值分析、监控量测与经济核算表明： 联合支护技术能够有效提高基坑边坡稳定性，满足“安全、高效、经济”的施工与生产需求。

Research on Stability and Support Technology ofDeep and Large Foundation Pit Slope with Existing Muck Overload

Based on the strength reduction theory, the instability mechanism of a deep and large foundation pit slope in Chongqing under surrounding muck overload is studied using numerical simulation and in situ monitoring. The conclusions are drawn as follows. (1) The potential destructive type of slope with surrounding muck load is shearing and slide, and the inner essence of slope instability is that the maximum shear ratio is formed and extended from toe to top of slope, and is connected in the banded form. (2) The support method of soil layer is "large slope and mesh spray", and the soil slope ratio is 1∶1.75. (3) The support method of rock layer is "low slope and bolt mesh spray", and rock slope ratio is 1∶0.75. According to numerical simulation, in situ monitoring and economic calculation, the stability of foundation pit slope can be improved and the requirements of safe, high efficiency and economy can be met.