| With the development of China’s traffic construction,urban subway construction was increasingly developed,limited by urban public roads and surrounding buildings(structures).The construction of metro tunnels would inevitably take on the posture of upward or downward slopes,which would easily cause disasters such as instability and collapse in front of the cutterhead,and imposed stricter requirements on the adjustment of the shield construction and posture.This article took Zhengzhou Metro Line 14 Civil Culture Service Area Underground Traffic Engineering D Contract Section Municipal Party School Station～Olympic Sports Center Station～Xingkong Road Station shield section as the engineering background.In this paper,theoretical calculation,numerical simulation and on-site monitoring were combined to study the stress changes,the law of surface settlement caused by excavation of large-slope shield tunnel,the determination of ultimate support force of excavation surface and the sensitivity of multiple influencing factors.The main research work was as follows:(1)The simulation calculation of shield tunnel construction under different line gradients showed that the ground loss caused by tunnel excavation made the horizontal displacement X point to the center of the tunnel as a whole;The curve of vertical displacement Z above the tunnel presented a normal distribution.With the increase of depth,the vertical displacement increased and the range of disturbance decreased.At the same time,the horizontal displacement X of surface increased with the increase of line gradient,while the surface subsidence Z showed a quadratic parabolic decreasing trend.(2)Linear regression analysis was used to analyze the ground subsidence data of shield tunnel section between Party School and Olympic Sports Center Station of Zhengzhou Metro Line 14.By introducing correction coefficients α and β,the maximum settlement value Smax and width I of settling tank in Peck’s empirical formula were corrected.It was concluded that when the correction factors α and β are between 0.33～0.73 and 0.6～1.0,the improved Peck curve was more consistent with the field measurement,and the prediction effect was good.(3)Stress support ratio and ultimate support pressure were introduced successively.With the decrease of support force,the displacement of soil in front of excavation increased continuously.When the support force of excavation face was reduced to a certain extent,that was,when A=0.2,the horizontal displacement of soil changed suddenly and the excavation face losed stability.It was considered that the corresponding support force of excavation face was the minimum limit support force,that was 29.42 kPa.(4)Through the analysis of the failure forms of the soil in front of the shield tunnel excavation,it was found that the deformation caused by the shield tunnel mainly occured at the excavation face,and gradually developed from the top of the excavation face to the surface.(5)The influence of key parameters such as line slope,tunnel depth,friction angle and cohesion in soil on the ultimate support force of excavation face was analyzed and the corresponding laws were revealed.With the increase of tunnel burial depth,the ultimate support stress ratio of excavation face increased.When the burial depth of shield tunnel exceeded a certain extent,the increase of the limit support stress ratio slowed down gradually due to the"arching" effect of the overlying soil of the shield tunnel,which was a quadratic function.The stability of excavation face increased with the increase of soil cohesion,and the ultimate support stress ratio decreased linearly.The stress ratio of limit support decreased quadratically with the increase of friction angle in soil.With the increase of the slope angle of the line,the excavation surface becomed more and more unstable,and the required ultimate support stress ratio becomed higher and higher,showing a linear growth. |
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