弱节理小净距隧道合理净距及围岩稳定性研究

Study on Reasonable Clear Distance and Surrounding Rock Stability of Weak Jointed Small Clear Distance Tunnel

为了研究弱节理小净距隧道的合理净距及围岩的稳定性,以大荒沟小净距隧道工程为研究背景,基于量化GSI围岩评级系统,确定了弱节理隧道围岩力学参数;基于Hoek-Brown强度准则的应变软化模型,采用FLAC3D软件模拟得到0.9B^1.7B净距条件下隧道中夹岩柱塑性区分布,分析了中夹岩柱的稳定性,确定了弱节理小净距隧道的最小合理净距。通过理论方法计算了小净距隧道围岩压力,进行支护结构设计。通过FLAC3D软件分别对支护条件下小净距隧道采用二台阶法、单侧壁导坑法、双侧壁导坑法、CD法、CRD法、环形开挖预留核心土法进行数值模拟,分析不同工况下围岩拱顶位移及水平位移的分布特征,选择合理的施工方法,优化隧道开挖支护方案。研究结果表明:采用FLAC3D数值模拟得到不同净距条件下中夹岩柱塑性区分布情况,能够确定隧道最小合理净距;采用FLAC3D数值模拟分析不同开挖工况条件下围岩的变形规律,确定了环形开挖法为理想的施工方法;通过现场监测分析可知,选择1.5B净距及环形开挖预留核心土法施工较为合理,锚喷支护与中夹岩柱长锚杆共同作用,能对约束小净距隧道双洞开挖后中夹岩柱松动圈的发展起到重要作用。

In order to study the reasonable clear distance of weak jointed small clear distance tunnel and surrounding rock stability, taking the Dahuanggou small clear distance tunnel project as the research background, the mechanical parameters of the surrounding rock of the weak jointed tunnel are determined based on the quantified GSI surrounding rock rating system. Based on the strain softening model of Hoek-Brown strength criterion, the distribution of plastic zone of the middle rock pillar under the condition of 0.9B-1.7B clear distance is simulated by FLAC3 D. The stability of the middle rock pillar is analyzed, and the minimum reasonable clear distance of the tunnel is determined. The surrounding rock pressure of small clear distance tunnel is calculated by theoretical method, and the supporting structure is designed. The numerical simulation of the supported small clear distance tunnel is carried out by two-step method, single-side wall heading method, double-side wall heading method, CD method, CRD method and the method of ring type excavation with conserved core soil using FLAC3 D. The distribution characteristics of surrounding rock vault displacement and horizontal displacement under different working conditions are analyzed, and a reasonable construction method is selected to optimize the tunnel excavation and support scheme. The result shows that(1) The minimum reasonable clear distance of the tunnel can be determined by the plastic zone distribution of the middle rock pillar under different clear distance conditions obtained by FLAC3 D numerical simulation.(2) By analyzing the deformation rule of the surrounding rock under different excavation conditions using FLAC3 D numerical simulation, the method of ring type excavation with conserved core soil is determined as the ideal construction method.(3) According to field monitoring and analysis, it is reasonable to choose 1.5B clearance and the method of ring type excavation with conserved core soil for construction. The combined action of anchor shotcrete support and long rock bolts in the middle rock pillar can play an important role in restricting the development of the middle rock pillar loose circle after the excavation of the double holes in the small clear tunnel.