广州某紧临地铁车站土岩组合深基坑,开挖深度大,周边环境复杂,变形控制要求非常严格。依据实际监测数据,详细分析了基坑施工各阶段的围护结构变形、土岩体侧移、支撑轴力、锚索拉力及周边环境沉降的变化规律。分析结果表明:围护墙与外侧土岩体最大水平位移均发生在土岩结合面附近;基坑开挖结束至底板施工期间,围护墙及外侧土岩体水平变形呈蠕变特点;地下室采用的“复合墙”及跳仓法施工技术,使施工完毕后的围护墙、土岩体水平位移均发生了明显回弹,最大水平位移约为开挖至基底时的40%~60%;开挖引起的周边地面沉降最大值发生在离坑边0.5倍开挖深度附近,沉降值约为邻近围护墙最大水平位移的0.47倍;条件允许时,土岩组合基坑可优先采用支撑+锚索组合支护方案。本工程的监测数据相互印证,揭示了该土岩深基坑在各种条件下的实际工作状况,可为类似情况深基坑的设计与施工提供参考。

A deep foundation pit of soil-rock combination adjacent to metro station is located in Guangzhou. The excavation depth is large, and the surrounding environment is complex, and the deformation control requirements are very strict. Based on the actual monitoring data, the variation laws of surrounding structure deformation, lateral displacement of soil and rock mass, support axial force, anchor cable tension and surrounding environment settlement in each stage of foundation pit construction were analyzed in detail. The results show that the maximum horizontal displacement of the retaining wall and the surrounding soil and rock mass occurs near the soil-rock interface; from the end of foundation pit excavation to the construction of floor, the horizontal deformation of retaining wall and lateral soil and rock mass presents creep characteristics; the construction technology of "composite wall" and the hopping method adopted in basement make the horizontal displacement of retaining wall, soil, and rock mass rebound obviously after construction, and the maximum horizontal displacement is about 40%~60% when the basement is excavated; the maximum ground subsidence caused by excavation occurs near the excavation depth of 0.5 times from the pit edge, and the settlement value is about 0.47 times of the maximum horizontal displacement of the adjacent retaining wall. If the conditions permit, the support + anchor cable combination support scheme can be preferred for the soil-rock composite foundation pit. The monitoring data of this project confirm each other and reveal the actual working conditions of this deep foundation pit under various conditions, which can provide reference for the design and construction of similar deep foundation pit.

重庆地区土岩基坑随处可见,在涉及这类基坑的稳定性计算时,设计者往往强调的是整个基坑开挖面岩土体的稳定性,却忽视了基坑岩层以上土体的稳定性。针对此种情况,推导出了这类地质条件下的基坑在采取垂直开挖或放坡时,上层土体沿某一平面滑动的稳定性计算模式,并提出了土岩交界处以上土体稳定性的判别标准,以及可以采取的相应施工措施。通过工程实例与理论计算的对比分析,证明了此种判别标准和施工措施不仅能保证基坑的稳定性,同时也有利于降低工程造价,为今后类似工程提供有益的借鉴。

Soil-rock composite pits can be seen everywhere in Chongqing city. However, when referring to the stability calculation of these pits,the designers tend to emphasize the stability of rock-soil mass on the excavation surface of the whole pit and ignore the stability of upper soil.In this paper,a stability calculation mode is deduced in the case that the upper soil slides along a plane when vertical excavation or step-slope excavation is taken for the pit. At the same time, the criterion of the stability of soil above the junction between the soil and rock is proposed, then,the measures dealing with these cases are also put forward. By comparing the result of theoretical calculation with engineering examples, the criterion and construction measures are proved to be effective both in the stability of the pits and in reducing project cost, which will hopefully serve as beneficial references to similar engineering.