深基坑局部深坑突涌稳定性计算研究

Calculation of inrushing stability of local pits in deep excavation

突涌稳定性关乎基坑安全和造价,而局部深坑是深基坑中突涌破坏最薄弱部位。基于局部深坑坑底土体沿铅垂面整体剪切破坏的假定,提出可考虑坑底土体抗剪强度、深坑几何尺寸和坑底加固的突涌稳定性计算公式,并研究计算公式适用范围和坑底土体抗剪强度计算方法。通过对杭州钱塘江两岸大量已安全施工完成深基坑工程的计算分析,得出以下结论:考虑原状土抗剪强度可使突涌稳定系数增加30%以上,常规坑底加固使其进一步增加20%左右,计算结果符合实际情况;坑底隔水层的侧面积和顶面积的比值越大,突涌稳定性越好;平面尺寸较大的基坑可通过分块开挖来确保突涌稳定性。

Inrushing may lead to a high construction cost or even failure of excavation, while local deep pit, including elevator shaft and collecting well, is the most dangerous place of inrushing in the deep excavation. Based on the assumption of general shear failure of soils between the pit bottom and the confined aquifer top, an equation is proposed to evaluate the inrushing stability of local deep pit, which can consider the effect of soil shear strength, plan size and reinforcement. Applicable conditions of the formula and the method to calculate the shear strength are also provided. Finally, the data of deep excavations along the Qiantang River in Hangzhou are analyzed. The following conclusions are drawn： （1） the shear strength has an increase of more than 30% in inrushing stability and an extra increase of about 20% in stability is achieved by reinforcement of pit bottom soils; （2） the possibility of inrushing decreases with the increase of the height of pit bottom soils and the ratio of pit circumference to pit area; （3） it can prevent inrushing by dividing a large excavation into lots of small ones.