A rigorous adaptive lower bound limit analysis method with 3-noded element (LB-FELA) is adopted to discuss the tunnel stability and failure mechanism of dual unlined horseshoe-shaped tunnels in non-homogeneous clays. The clays mass has heterogeneity, where the shear strength increases linearly with depth. This problem is defined as a plane strain analysis model. The calculation results are provided using the dimensionless stability numbers, which are affected by dimensionless parameters $C/D$, $S/D$ and $\rho D/c_0$.The typical failure mechanisms of the dual horseshoe-shaped tunnels are presented based on the parametric studies using the final refined meshes of the proposed method. The results show that the dimensionless parameters $\rho D/c_0$, $C/D$,and $S/D$ have great influences on tunnel stability and failure mechanism of the dual horseshoe-shaped tunnels. Using the calculation results provided by this paper, the tunnel designers can directly evaluate the stability of the tunnel in non-homogeneous clays.

采用严格的三节点自适应下界分析法（LB-FELA），探讨了非均质黏土中双单衬马蹄形隧道的稳定性和破坏机理。粘土块具有非均质性，其中剪切强度随深度线性增加。这个问题被定义为平面应变分析模型。计算结果是使用无量纲稳定性数提供的，该数受无量纲参数的影响$C/d$， $\mathrm{小号}/d$ 和 $\rho d/C_0$通过对所提方法的最终细化网格进行参数研究，提出了双马蹄形隧道的典型破坏机理。结果表明，无量纲参数$\rho d/C_0$， $C/d$，和 $\mathrm{小号}/d$对双马蹄形隧道的稳定性和破坏机理影响很大。利用本文提供的计算结果，隧道设计人员可以直接评估非均质黏土中隧道的稳定性。