预留土堤对深基坑力学性状的影响分析

Analysis of influence of reserved soil embankment on mechanical properties of deep foundation pit

预留土堤在基坑支护中应用广泛,但在设计计算时往往以经验为准,存在一定的盲目性和不确定性。依托在建工程,采用FLAC3D建立了数值分析模型,通过改变预留土堤的高度和宽度,研究了基坑支护桩水平位移、基坑周边地表沉降、桩身弯矩、安全系数以及潜在滑动面的变化规律,最后提出了经济合理的预留土堤设计参数。结果表明:基坑支护桩的最大位移发生在桩顶,基坑周边地表沉降呈“凹槽形”分布,最大沉降量距离基坑边缘2~3 m;桩身弯矩沿桩长呈“鼓肚形”变化规律,峰值点在距离桩底8~12 m处;桩前预留土堤的设计宽度不应大于8 m,否则对于减小支护桩位移和弯矩、基坑周边地表沉降益处不大,而且会占用基坑有限的施工作业面;桩前预留土堤的高度不应大于5 m,否则其稳定性将难以保证。

The reserved soil embankment is widely used in the support of foundation pit,but the design calculation is often based on experience,which has certain blindness and uncertainty.Based on the constructing project,a numerical analysis model was established by using FLAC3D.By changing the height and width of the reserved soil embankment,the variation laws of horizontal displacement of foundation pit support pile,surface settlement around the foundation pit,pile bending moment,safety factor and potential sliding surface were studied.Finally,economic and reasonable design parameters of the reserved soil embankment were proposed.The results show that the maximum displacement of foundation pit support pile occurs at the top of the pile,the surface settlement around the foundation pit presents a"groove"distribution,and the maximum settlement is 2-3 m away from the edge of the foundation pit.The bending moment of the pile body shows a"bulge shape"variation rule along the pile length,and the peak point is 8-12 m away from the pile bottom.The design width of the reserved soil embankment in front of the pile should not be more than 8 m,otherwise it will have little benefit to reducing the displacement and bending moment of the support pile and the surface settlement around the foundation pit,and will occupy the limited construction surface of the foundation pit.The height of the reserved soil embankment in front of the pile should not be more than 5 m,otherwise its stability will be difficult to ensure.