盾构隧道穿上软下硬地层掌子面顶推力优化研究

上软下硬复合地层是盾构施工中经常遇到的一类地质状况,在这种特殊地层条件下进行盾构施工有很多难点,结合深圳地铁7号线穿越上软下硬交界地层的工程实例,采用数值模拟的计算方法,对盾构隧道穿上软下硬复合地层(“由软入硬”及“由硬入软”)掌子面各分区内顶推力进行优化分析,结果表明:在盾构掘进穿越上软下硬地层的过程中,适当减小上部分区内千斤顶推力并增大下部分区顶推力的措施可以有效减小“由软入硬”段管片应力(S1减小2.76%~3.1%、S3减小3.39%~3.46%),并得出掌子面上中下分区内千斤顶推力的比例在8∶13∶18~10∶13∶16范围内较为合理。但这种调整盾构姿态的措施会使地表沉降出现增大趋势,而在实际工程中则可以适当增大土仓压力来抑制地表沉降的增大。

Optimization Study on Jacking Force of the Tunnel Face when Shield Tunnel Crossing the Upper-soft and Lower-hard Stratum

The upper-soft lower-hard composite stratum is a kind of special geological conditions frequently encountered in shield construction, but there are many difficulties in shield construction under such stratum conditions. Based on the shield tunnel engineering crossing the upper-soft lower-hard stratum in Shenzhen Metro Line 7 Project, numerical simulation method is used to optimize different jacking force schemes of each partition in tunnel face when tunnel crossing the upper-soft lower-hard composite stratum (stratum crossed by tunnel “from the soft into hard” and “from the hard into soft”). The calculation results indicate that measures of properly decreasing the jacks’ thrust of upper partition and increasing the jacks’ thrust of lower partition in the tunnel face could effectively reduce the stress of segments in the stratum crossed by tunnel “from the soft into hard” (S1 decreases 2.76~3.1%, S3 decreases 3.39~3.46%), and it also suggests that proportion of jacks’ thrust of the upper, middle and lower parts in tunnel face within the range 8∶13∶18~10∶13∶16 is reasonable. However, such adjustment measures of shield posturer will make the ground subsidence show an increase tendency, so we can also increase the soil pressure properly to restrain the increase tendency of ground subsidence in the actual project.