高应力炭质板岩隧道开挖支护结构受力评价研究

为探究高应力下炭质板岩隧道开挖过程中围岩位移、支护结构内力变化规律，依托渭武高速木寨岭公路隧道，采用有限差分软件FLAC3D建立三台阶七步开挖法下炭质板岩隧道的数值模型，提出强、中、弱三种支护方案；分析开挖距离对围岩位移、支护结构内力等因素的影响，并对支护设计参数合理性评价。研究结果表明：开挖过程中围岩累计沉降和收敛变形量比较：强支护＜中支护＜弱支护；开挖相同距离下，随着支护强度上升，支护提供的弹性抗力越强，围岩沉降和收敛变形减小；以强支护为例，支护结构轴力呈现先增大后减小的趋势，最终轴力不断上升但趋势变缓的特征，开挖距离50m趋于稳定；支护设计参数评价时，开挖距离（50m）结束，强、中、弱三种方案钢架受压安全系数最小值分别为3.903、3.718、3.264，#1拱顶处强支护钢架较喷射混凝土先破坏，混凝土安全系数最小值分别为3.491、2.987、2.666，#2左拱腰处喷射混凝土较钢架先破坏，故选择中支护方案，材料I25b×C25、初衬厚度26cm、钢架距离0.8m。研究结果可为类似软岩隧道开挖和支护结构的设计提供一定参考。

Study on stress evaluation of excavation supporting structure of high ground stress carbonaceous slate tunnel

Aiming to explore the variation law of surrounding rock displacement and internal force of supporting structure during the excavation of carbonaceous slate tunnel under high stress, based on the Muzhailing Highway Tunnel of Weiwu Expressway, the finite difference software FLAC3D is used to establish the numerical model of carbonaceous slate tunnel under three-bench seven-step excavation method, and three supporting schemes of strong, medium and weak are proposed. The influence of excavation distance on the displacement of surrounding rock and the internal force of supporting structure is analyzed, and the rationality of supporting design parameters is evaluated. The results show that the cumulative settlement and convergence deformation of surrounding rock during excavation are compared: strong support < medium support < weak support; under the same distance of excavation, with the increase of support strength, the elastic resistance provided by support is stronger, and the settlement and convergence deformation of surrounding rock decrease. Taking the strong support as an example, the axial force of the supporting structure shows a trend of increasing first and then decreasing. Finally, the axial force continues to rise but the trend slows down and the excavation distance is 50 m, it tends to be stable. In the evaluation of supporting design parameters, when the excavation distance (50m) is over, the minimum safety factors of steel frame compression in strong, medium and weak schemes are 3.903,3.718 and 3.264 respectively. The steel frame of strong support at # 1 vault is destroyed earlier than that of shotcrete, and the minimum safety factors of concrete are 3.491,2.987 and 2.666 respectively. The shotcrete at # 2 left arch waist is destroyed earlier than that of steel frame, so the medium support scheme is selected, material I25b × C25, initial lining thickness 26cm, steel frame distance 0.8m. The research results can provide some reference for the excavation and support structure design of similar soft rock tunnels.