考虑应力路径的深埋隧道黏弹–塑性围岩与支护相互作用

Interaction between viscoelastic-plastic surrounding rock and support structure in deep tunnels considering stress path

黏弹–塑性岩体中,隧道的支护反力会随时间增加,致使塑性区内已屈服围岩的应力状态从屈服面上回到屈服面以内。因此,研究隧道围岩与支护结构相互作用的长期力学特性时须先弄清其应力路径。考虑应力路径影响,基于广义Kelvin流变模型和Mohr-Coulomb强度准则,给出深埋隧道黏弹–塑性围岩与支护相互作用的应力、应变及位移的简化计算方法。将高地应力软岩隧道的各种"抗让结合"支护技术归纳为"先让后抗"、"边让边抗"、"先控再让后抗"3类,分别分析3类支护措施对围岩应力路径的影响,并对比研究不同支护措施下隧道黏弹–塑性围岩的变形及支护反力。结果表明,考虑应力路径后计算得到的围岩位移更大。在相同的位移释放量、相同的衬砌支护刚度条件下,采用"先让后抗"的措施,围岩初期变形速率非常大,施加永久支护后,后期增长的支护反力也最大。在高地应力、变形严重的条件(例如初始地应力超过20 MPa)下采用"先控再让后抗"措施是最合适的。隧道开挖后立即施作长锚杆主动支护围岩,不仅可以控制围岩在第一阶段的变形速率,提高第一阶段围岩的稳定性,还可以大幅降低第二阶段永久衬砌的支护力,提高第二阶段衬砌结构的稳定性。在地应力不高、变形不严重的条件下(例如初始地应力低于10 MPa)采用"先让后抗"的措施就可以较好地控制围岩变形,不必采用"先控再让后抗"措施。而"边让边抗"措施适用于2种情况之间(例如初始地应力为10~20 MPa)。此外,黏滞系数较小(较软弱)的围岩开挖后变形速率较大,例如当黏滞系数η分别取2×109和1×1010 Pa·d时,采用"先控再让后抗"措施后围岩初期变形速率分别为17.6和3.5cm/d。因此,黏滞系数较小(较软弱)的围岩在开挖后必须立即施加较大的支护反力以控制围岩变形速率。

The support reaction force of tunnels increases with time in viscoelastic-plastic rock mass,which makes the stress state of yielding surrounding rock in plastic zones move inward from the yield surface.Therefore,it is necessary to make clear the stress path of the surrounding rock when investigating the long-term mechanical characteristics of the interaction between rock and tunnel support.Considering the effect of the stress path,based on the generalized Kelvin model and Mohr Coulomb strength criterion,a simplified method for analyzing the viscoelastic-plastic stress,strain and displacement of the surrounding rock and the interaction between the support and the surrounding rock is proposed.In this paper,different kinds of“yield-resist combination”support technologies of high geostress soft rock tunnels are summarized into three categories as“yield before resist”,“yield while resist”and“control-yield-resist”.The influences of three kinds of support measures on the stress path of the surrounding rock are analyzed respectively.The deformation of the viscoelastic-plastic surrounding rock and the support reaction under different support measures are further studied.The results show that the calculated surrounding rock displacement is much larger if the stress path is taken into account.Under the condition of the same displacement release and the same stiffness of the lining support,the deformation rate of the surrounding rock at the initial stage is very large by adopting the measure of“yield before resist”,and the increasing support reaction force at the second stage is also the largest after applying the permanent support.It is most appropriate to adopt the“control-yield-resist”support measure under the condition of high geostress and serious deformation(for example,the initial stress exceeds 20 MPa).The prestress long bolt is employed to support the surrounding rock immediately after the tunnel excavation,which can not only control the deformation rate and improve the stability of the surrounding rock in the first stage,but also greatly reduce the additional support force and improve the stability of the lining structure during the second stage.Under the condition of low geostress and slight deformation(for example,the initial stress is less than 10 MPa),the“yield before resist”measure can effectively control the deformation of the surrounding rock,and the“control-yield-resist”measure is not necessary.The“yield while resist”measure is applicable to the cases between the above two extreme conditions(e.g.,the initial ground stress is between 10 and 20 MPa).In addition,the deformation rate of the surrounding rock with a small viscosity coefficient is very large after excavation,for example,when the viscosityη=2×109 and 1×1010 Pa·d,the initial rock deformation rates are 17.6 and 3.5 cm/d respectively with the“control-yield-resist”measure.Therefore,for the surrounding rock with a small viscosity,large support reaction force must be applied immediately after excavation to control the deformation rate.