白马隧道软弱围岩掌子面稳定性研究

Research on the Face Stability in Soft Surrounding Rock of Baima Tunnel

高地应力软弱围岩条件下隧道施工易发生掌子面失稳坍塌。依托九绵高速白马隧道,采用颗粒流数值模拟软件PFC建立三维离散地层模型,利用FLAC内置命令生成小导管和锚杆连续结构单元,构建离散-连续耦合模型,以此分析不同支护方案对掌子面稳定性的影响。研究结果表明,采用小导管超前支护后,在掌子面前方2 m内,拱顶沉降约为未支护的60%,在掌子面后方1 m内,拱顶沉降仅为未支护的40%,长短小导管对拱顶沉降的控制效果差异不大。锚杆径向支护后,位移量随着与隧道距离的增大基本呈线性递减规律,相对于4 m短锚杆,8 m长锚杆作用下围岩位移递减更快,掌子面上方围岩的松动高度更小,更能有效地降低掌子面上方围岩坍塌的风险。研究成果对类似工程具有一定的参考价值。

Tunnel construction under the condition of high ground stress and weak surrounding rock is easy to lead to the collapse of tunnel face.Based on the Baima tunnel of Jiumian expressway project,this paper establishes a 3D discrete stratum model by using the particle flow numerical simulation software PFC.The small pipes and bolts continuous structural unit are generated using built-in commands of the finite difference software FLAC.The discrete-continuous coupled model is established to analyze the influence of different supports schemes on the stability of tunnel face.The results show that after adopting advanced small pipes,the settlement of the vault is about 60%of the unsupported in 2 m ahead of the palm face,and only 40%of the unsupported in 1 m behind the face.However,there is little difference between long and short pipes in controlling vault settlement.The displacement of the surrounding rock decreases linearly with the increase of distance from tunnel under the support of bolts.Compared with 4 m short bolts,the displacement of surrounding rock decreases faster under the action of 8 m long bolts,especially the loose height of surrounding rock above the palm face.Thus,the risk of surrounding rock collapse above the palm face can be reduced more effectively.The research results have certain reference value for the similar projects in the future.