穿越分层地层的盾构隧道开挖面稳定机理研究

基于塑性力学极限分析上限法,通过空间离散技术,建立圆形盾构隧道穿越分层地层时开挖面失稳的三维破坏机构,推导盾构开挖面极限支护压力的计算方法,获得最优上限解。针对单一地层,将极限支护压力计算方法与前人提出的3种多块体模型计算方法进行对比,分析黏聚力、内摩擦角等强度参数差异对极限支护压力的影响,同时验证本文方法的准确性。针对2种地质强度差异较大地层,将此方法和数值模拟计算的极限支护压力进行对比,研究地层差异性对极限支护压力的影响,发现2种方法计算结果吻合度较高。研究表明:极限支护压力随上部软弱地层在开挖断面竖直方向上的厚度占开挖断面总高度的比例增大而增大,并随地层内摩擦角、黏聚力差异的增大而增大。

Stability Mechanism of Excavation Face of Shield Tunnel Crossing Layered Strata

Based on the upper bound method of limit analysis in plastic mechanics, a three-dimensional failure mechanism for the excavation face instability of circular shield tunnel crossing layered strata was established by means of spatial discretization technology. The calculation method for the ultimate support pressure of the excavation face of shield tunnel was deduced and the optimal upper bound solution was obtained . In the case of single stratum, the calculation method for ultimate support pressure was compared with the three calculation methods of multi-block model previously proposed. The influence on the ultimate support pressure due to different strength parameters, such as cohesion and internal friction angle , was analyzed, and the accuracy of this method was verified. In the case of two strata with different geological strengths, the calculation results of this method were compared with the ultimate support pressure calculated by numerical simulation to study how the difference of strata affecting the ultimate support pressure. It was found that the fitting degree of the calculated results of the two methods was relatively high. Research shows that the ultimate support pressure increases with the increase of the proportion of the thickness of the upper weak stratum in the vertical direction of the excavated section to the total height of the excavated section, and increases with the increase of the difference of friction angle and cohesion in the stratum.