The nonlinear Baker failure criterion is introduced into the upper-bound limit analysis to examine the face stability of a shallow tunnel. The tunnel face under the ultimate limit state is analyzed from the perspective of energy balance. The work rates of external forces and internal energy dissipation are calculated. An analytical solution of necessary face pressures is derived. The optimal upper-bound solution of the face pressures is obtained by optimization. The results show that the three dimensionless parameters A, T, n of nonlinear Baker failure criterion have different effects on the necessary face pressures and the pattern failure mechanisms ahead of tunnel face. A is the most important one; n takes the second place, and T is the least one. The computed necessary face pressures are nonlinearly increasing when A is reduced. Combined with the actual monitoring data of Taxia tunnel, the calculation results in this paper is verified. It is suggested that the tunnel face supports should be strengthened timely in soft rocks to prevent the occurrence of face collapse.%将非线性Baker破坏准则引入到极限分析上限定理中,分析浅埋巷道掌子面的稳定性问题.从能量角度分析极限状态下掌子面的受力状态,计算破坏过程中所产生的外功率和内能损耗率,推导围岩压力的解析解,采用Matlab软件序列二次规划算法得到围岩压力的最优上限解.研究结果表明,非线性Baker破坏准则中的三个无量纲参数A,T,n对掌子面围岩压力以及破坏范围的影响均各不相同.A的影响最大,n次之,T最小;并且当A减小时掌子面的围岩压力和破坏范围均非线性增大.结合浙江省丽水市隧下隧道的实际监测资料,对计算结果进行了验证.建议针对软岩巷道应及时加强掌子面的支护措施,防止发生坍塌事故.
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