Modeling stress wave propagation in rocks by distinct lattice spring model

In this paper, the ability of the distinct lattice spring model （DLSM） for modeling stress wave propagation in rocks was fully investigated. The influence of particle size on simulation of different types of stress waves （e.g. one-dimensional （1D） P-wave, 1D S-wave and two-dimensional （2D） cylindrical wave） was studied through comparing results predicted by the DLSM with different mesh ratios （It） and those obtained from the corresponding analytical solutions. Suggested values of lr were obtained for modeling these stress waves accurately. Moreover, the weak material layer method and virtual joint plane method were used to model P-wave and S-wave propagating through a single discontinuity. The results were compared with the classical analytical solutions, indicating that the virtual joint plane method can give better results and is recommended. Finally, some remarks of the DLSM on modeling of stress wave propagation in rocks were provided.

Stability analysis on tunnels with karst caves using the distinct lattice spring model

The effects of karst caves on tunnel stability were numerically investigated using the distinct lattice spring model(DLSM).The DLSM was validated by investigating the mechanical behavior of Brazilian discs with various sizes of central circular holes.Then,the effects of karst cave on U-shaped tunnel were investigated under various karst caves positions(top,bottom,and right side of the tunnel),tunnelcave distances(0.5-4 times the radius of the tunnel arc),and cave shapes(circular,rectangular flat,and rectangular vertical caves).The failure processes of the tunnel under those various conditions were analyzed and both the failure process and the final failure patterns of the tunnel were discussed.Numerical simulation demonstrated that karst caves around the tunnel could weaken the stability of the tunnel,indicating tunnel-cave distance effects.The closer the cave to the tunnel,the weaker the tunnel under loading.This effect was not significant when the tunnel-cave distance(d)was larger than three times the tunnel arc radius(R).In addition,the final failure pattern of the tunnel and its surrounding rock mass were dependent on both the position and the size of the cave.The larger the cave,the weaker the tunnel and its surrounding rock mass.Furthermore,compared with those cases with top and bottom caves,the tunnel with a right side cave had more impacts on tunnel stability.The main research finding could help engineers carry out stability analysis on tunnels in karst areas and take effective measures to enhance tunnel stability.

基于数值仿真的复杂岩体TBM掘进性能评估模型

为了评估全断面隧道掘进机(TBM)在复杂岩体环境中的掘进性能,本文提出了基于数值仿真的全断面TBM掘进预测模型。首先,采用4D-LSM和DDA耦合模型数值重现工程尺度完整岩体和节理岩体的TBM掘进测试过程,分析全断面TBM掘进过程中刀盘的力学响应和岩体的破坏特征;其次,研究节理间距、节理方向、岩体单轴抗压强度以及脆性指数对可钻性指数的影响;最后,引入单神经元对数值仿真预测模型进行修正,并与岩体特征模型进行对比分析,验证基于数值仿真的全断面TBM掘进性能预测模型的适用性。研究结果表明:TBM在低强度、高脆性以及节理发育的岩体中掘进效率更高,当节理面与TBM掘进方向之间的夹角为60°~75°时,最有利于TBM的运行。基于数值仿真的TBM掘进性能预测模型提供了一种经济、灵活的可用于评估复杂环境中TBM施工性能的方法。