水土耦合对盾构土拱效应及最小支护力的影响分析

Analysis of Effects of Soil and Ground Water Coupling on Soil Arching and Minimum Face Pressure in Shield Tunneling

盾构隧道开挖面最小支护力与开挖面上方土拱效应密切相关。模型试验结果显示,地下水的存在会减小开挖面上方土拱高度;数值计算结果表明,砂土内摩擦角变化是地下水影响土拱高度的主要方式。针对此现象,本文结合楔形体模型对开挖面最小支护力计算方法进行分析,提出计算开挖面最小推力的修正系数,即通过对上方棱柱体受到的侧土压力系数进行修正来体现地下水对开挖面上方土拱效应的影响。分析结果表明:地下水的存在能够减小最小支护力与上覆土压力的比值,有利于土体稳定;在最小支护力计算中需采用饱和砂土的有效内摩擦角,否则将降低开挖面安全系数。

The minimum supporting force of the excavation face is closely related to the soil arching effect above the tunnel face.The results of the model test concluded that the existence of groundwater can reduce the height of the soil arching above the tunnel face.Numerical analysis showed that the change of the internal friction angle of sand was the key factor of ground water affecting soil arch height.In response to this situation,the calculation method of the minimum supporting force of the excavation face was analyzed based on the wedge model.The correction factor for calculating the minimum thrust of excavation face was presented.The lateral earth pressure coefficients of the prism above the wedge were updated to reflect the influence of ground water on the soil arch above the excavation face.The analysis results showed that the existence of groundwater can decrease the ratio of the minimum supporting force and the pressure of the overlying soil,which is beneficial to the stability of the soil.The effective angle of internal friction of saturated sand should be used in the calculation of the minimum supporting force,otherwise the safety factor of excavation face will be lowered.