Due to clay creep characteristics,the long-term shield shutdown in the clay stratum will induce secondary risks such as excessive increase in the total thrust,difficult attitude control for shield tunnelling and the segment breakage.In this study,the creep characteristics were described by Burgers'constitutive relation.The mechanical model of deep-buried shield tunnel in clay stratum considering its weight was established.The viscoelastic solution of the contact stress between shield and surrounding stratum was derived based on the viscoelastic theory.The theoretical relation of the total thrust increment required for shield resuming tunneling and the shutdown time was obtained by integral and segment calculation.According to the shutdown examples of hydraulic tunnel,the measured and theoretical values of the total thrust increment were compared.The results show that the average relative error of the measured and theoretical values of the total thrust increment is 13.81%,which verifies the reliability of this analytical solution.The deeper the buried depth,the greater the total thrust increment,indicating that more attention should be paid to the thrust control when the shield resumes tunnelling after the shutdown at the deep buried tunnel.With the increase of the over-excavation clearance,the friction resistance of the shield shell decreases while the total thrust increment increases,and the total thrust increment decreases with the decrease of the friction coefficient.Therefore,it is effective for the secondary risk prevention during shutdown at deep buried tunnels to set appropriate over-excavation clearance and inject bentonite into the clearance for lubrication.
关键词
黏土蠕变特性/盾壳-地层接触应力/复推总推力增量/超挖间隙/摩擦因数
Key words
creep characteristics of clay/contact stress between shield and surrounding stratum/total thrust increment required for shield resuming tunneling/over-excavation clearance/friction coefficient
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