浅埋小净距隧道中夹岩柱稳定性及加固方案研究

为了探究小净距隧道中夹岩柱稳定性及加固方案,以四川德阳白竹山1号隧道为背景,基于普氏平衡拱理论,提出小净距隧道中夹岩柱上覆围岩压力计算公式,研究了小净距隧道上覆围岩压力影响因素。运用有限元软件MIDAS GTS NX建立浅埋小净距隧道三维模型,分析了在不同隧道净距工况下的围岩位移、塑性区分布以及中夹岩柱竖向应力分布情况,确定了合理净距。对中夹岩柱进行区域划分并对不同组合方式进行注浆加固,研究了不同加固方案对围岩变形的控制效果。研究结果表明:小净距隧道开挖方式、中夹岩柱加固措施和隧道净距直接影响平衡拱的形成以及上覆围岩压力的大小;白竹山1号隧道进口小净距段设计净距13.94 m是合理的;对中夹岩柱中岩盘采用小导管注浆加固极大地提高了中夹岩柱整体性和稳定性,限制了围岩变形。研究成果可为类似小净距隧道中夹岩柱最小安全净距及加固设计和施工提供参考。

Stability and Reinforcement Scheme of Middle Rock Column in Shallow-buried Tunnel with Small Clear Spacing

The aim of this research is to obtain the stability and explore the reinforcement scheme for the middle rock column of the Baizhushan No.1 Tunnel with small clear spacing in Deyang,Sichuan.On the basis of Protodyakonov's equilibrium arch theory,the formula of the pressure of surrounding rock overlying the middle rock column is proposed,and factors affecting the surrounding rock pressure on the tunnel are analyzed.Furthermore,the displacement of surrounding rock,the distribution of plastic zone,and the vertical stress distribution of the middle rock column with varied spacing are examined by establishing a 3D finite element model using MIDAS GTS NX.The reasonable clear distance is determined.In addition,the middle rock column is partitioned for grouting reinforcement of different combinations to study the control effect of different reinforcement schemes on surrounding rock deformation.Results demonstrate that the formation of equilibrium arch and the pressure of overlying surrounding rock are directly affected by the excavation method of tunnel,the reinforcement method of the middle rock column,and the clear distance of tunnel.The designed clear distance 13.94 m at the entrance of Baizhushan No.1 tunnel is reasonable.Small pipe grouting reinforcement for the middle rock column and the rock tray has greatly enhanced the integrity and stability of the middle rock column and restrained the deformation of surrounding rock.