地下大跨度隧道开挖支护过程的数值模拟

Numerical Simulation of Excavation and Supporting Process of Buried Large-span Tunnel

地下洞室开挖和支护过程的应力和应变状态对隧道工程安全性评估至关重要。文章采用LS-DYNA软件的动力松弛法确定围岩和结构的初始应力和应变状态,然后对开挖、喷锚支护和衬砌支护过程进行数值模拟,分析了围岩Von-Mises应力、塑性应变、最大主应变和位移变化情况。分析表明:开挖和支护方案对围岩应力和应变状态影响较大。大跨度地下工程在开挖和支护过程中出现的塑性变形主要局限于锚杆能够达到的区域,说明喷锚支护设计方案合理;另外,在围岩中会出现一定规模的拉伸应变,主要区域集中在围岩直墙和底板的交界处,但喷射混凝土和衬砌上没有塑性应变发生,拉伸应变的数值也很小;锚杆上的轴力远小于锚杆能承受的最大拉伸轴力,开挖和支护过程结束后整个结构系统均是安全的。

The stress and strain state is very important for tunnel safety assessment in process of excavation and support for buried tunnel. In this paper the dynamic relaxation method in LS-DYNA is used to determine the initial stress and strain of the surrounding rock and structures, and the process of excavation, shotcrete-bolt and lining support by numerical simulation were carried out. The change of Von-Mises stress, plastic strain, maximum principal strain and displacement of surrounding rock is analyzed. It is shown that the scheme of excavation and support have significant influence on the stress and strain of the surrounding rock. The plastic deformation in the process of excavation and support of large scale underground engineering is mainly confined to the area where the bolt can reach; it indicates that the scheme of shotcrete-boh support is reasonable. In addition, there will be certain of the tensile strain in the region of surrounding rock, mainly concentrated in the junction of the straight wall and the floor in the surrounding rock, but there is no plastic strain in the spray concrete and lining, and the value of tensile strain is also small. The axial force in the bolt is much smaller than the maximum tensile axial force which the bolt can bear and the whole structural system is safe at the end of excavation and supporting process.