土岩组合地层异形深基坑支护体系优化研究

Optimization of Support System for Deep Foundation Pit with Special-shaped Soil-rock Combination Strata

某明挖隧道基坑位于土岩组合地层,基坑大面深度约17.1 m,深挖部位约27.9 m,原设计整体基坑采用地下连续墙+4道钢筋混凝土支撑,坑中坑内侧壁采用钻孔灌注桩作为竖向支护结构,深坑部位加设2道钢管支撑。为节约工期和工程造价,综合考虑地层分布及地质条件,对原设计方案进行了系列优化。运用数值模拟对比分析了优化前后基坑支护体系和周边环境的变形特性,结果表明优化后的支护方案满足设计和规范要求。基坑按优化方案施工,并开展了现场监测工作,基坑监测结果表明:(1)基坑连续墙水平位移、地表沉降、支撑轴力、周边建筑物变形及坑底隆起等指标均小于控制要求;(2)连续墙最大水平位移发生在土岩分界面以上一定高度,最大值约为浅基坑深度的0.025%;(3)异形基坑两侧变形不对称,最大地表沉降发生在浅基坑侧,基坑外地表影响范围约为1.0H;(4)下部基岩段基坑开挖侧向变形量小,且对地表沉降槽范围影响不大。优化方案节约了工期和造价,可为类似基坑工程提供参考。

The foundation pit of a certain open-cut tunnel is located in a soil-rock combination layer,with a large depth of about 17.1 m and a deep excavation area of about 27.9 m.The original design of the overall foundation pit used underground continuous walls and 4 reinforced concrete supports,and the inner wall of the pit used drilled cast-in-place piles as vertical support structures.Two steel pipe supports were added to the deep pit area.To save construction period and project cost,a series of optimizations have been made to the original design scheme,taking into account the distribution of strata and geological conditions.Numerical simulation was used to compare and analyze the deformation characteristics of the foundation pit support system and surrounding environment before and after optimization.The results showed that the optimized support scheme met the design and regulatory requirements.The foundation pit was constructed according to the optimized plan and on-site monitoring work was carried out.The monitoring results of the foundation pit showed that:(1)The horizontal displacement of the continuous wall of the foundation pit,surface settlement,support axial force,deformation of surrounding buildings,and uplift at the bottom of the pit were all below the control requirements;(2)The maximum horizontal displacement of the continuous wall occurs at a certain height above the soil rock interface,with a maximum value of approximately 0.025%of the shallow foundation pit depth;(3)The deformation on both sides of the irregular foundation pit is asymmetric,and the maximum surface settlement occurs on the shallow foundation pit side.The impact range of the outer surface of the foundation pit is about 1.0H;(4)The lateral deformation of the foundation pit excavation in the lower bedrock section is small,and it has little impact on the range of surface settlement grooves.The optimization plan saves time and cost and can provide a reference for similar foundation pit projects.