Tunnel excavation was a typical three-dimensional space problem. As a two-dimensional numerical method, the combined finite-discrete element method did not demonstrate the spatial effect during the tunnel excavation simulation. A new excavation path for the combined finite-discrete element method was proposed based on the spatial evolution characteristics. Then, the tunnel excavation simulation was carried out under different excavation paths (linear softening curve, exponential softening curve, power softening curve, and new softening curve). The results showed that the advantages of the exponential softening curve and power softening curve were inherited by the new softening curve. The new softening curve demonstrated the spatial effect during the tunnel excavation simulation. Moreover, both the maximum softening rate and peak value of model kinetic energy occurred near the intermediate moment, which was an advantage over other softening curves. The discussion indicated that both the softening rate and elastic modulus range should be considered when determining new softening curve parameters. And the optimal total softening steps can be estimated by the proposed equation with an error tolerance. Finally, the new softening curve was well applied in the numerical analysis of tunnel excavation and support design.

中文翻译：

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有限离散元组合法隧道开挖数值分析方法研究


隧道开挖是一个典型的三维空间问题。作为一种二维数值方法，有限离散元组合法在隧道开挖模拟中没有表现出空间效应。基于空间演化特征，提出了一种新的有限离散元组合法开挖路径。然后，在不同开挖路径（线性软化曲线、指数软化曲线、功率软化曲线、新软化曲线）下进行隧道开挖模拟。结果表明，新的软化曲线继承了指数软化曲线和功率软化曲线的优点。新的软化曲线展示了隧道开挖模拟过程中的空间效应。而且，最大软化速率和模型动能峰值均出现在中间时刻附近，这比其他软化曲线具有优势。讨论表明，确定新的软化曲线参数时应同时考虑软化率和弹性模量范围。并且可以通过所提出的具有误差容限的方程来估计最佳的总软化步骤。最后，新的软化曲线在隧道开挖及支护设计数值分析中得到了很好的应用。