A new approach to simulate the supporting arch in a tunnel based on improvement of the beam element in FLAC3D

The beam element in FLAC3D can be used to simulate the supporting arch in a tunnel. However, this approach has the shortcoming of its constitutive model, and the bearing capacity and surrounding rock supporting effect of the arch model will be significantly exaggerated. To simulate the supporting arch in tunnel engineering well, a new approach is proposed by improving the beam element. The yield criterion of the beam element subjected to compression-bending loads is established based on the now-available bearing capacity formulas of some typical compression-bending sections. In addition, the yield criterion is embedded in the FLAC3D main program by using the FISH language, and the modification of the beam model and the yielding failure simulation of the supporting arch are finally implemented. Compression-bending tests and roadway tunnel arch support example analysis were performed. The results are as follows: (1) the modified model showed the dependence of the bending moment and axial force on the yielding action of the beam element under compression-bending loads; (2) the implementation program is effective and sensitive; (3) the computing deviation caused by the shortcomings of the original beam element model was effectively suppressed, the mechanical behavior and surrounding rock supporting laws exhibited by the arch model were much closer to reality, and the calculation accuracy and design reliability were improved by the new simulation approach.中文概要目 的基于常用的数值模拟软件FLAC3D进行二次开发, 弥补现有数值模拟方法的缺陷, 提出一种准确有 效的隧道/巷道拱架支护数值模拟方法。创新点1. 引入抗弯和抗压能力的相关性, 改进梁单元压 弯极限判据; 2. 通过FISH 语言编程, 实现梁单 元修正和拱架精确模拟。方 法1. 通过对FLAC3D 中梁单元支撑理论的分析, 明 确其存在的缺陷, 并利用算例进行证实(图4~6); 2. 基于传统强度理论, 对梁单元现有压弯极限判 据进行改进(图7 和8); 3. 通过FISH 语言编程, 实现梁单元修正模型嵌入(图9); 4. 通过算例分 析, 对新模拟方法的效果进行验证(图10 和13)。结 论1. 改进了梁单元压弯极限判据, 通过FISH 语言 编程实现了梁单元的修正及拱架屈服失效的模 拟。2. 构件压弯试验和巷道拱架支护实例分析表 明: 修正模型体现了在压弯组合荷载作用下梁单 元屈服时弯矩和轴力的相关性; 实现程序是有效 的且灵敏度较高; 提出的新模拟方法使计算偏差 得到有效压制, 拱架模型呈现出的力学行为及围 岩支护作用更加接近实际, 计算精度和设计可靠 度更高。