砂页岩缓倾地层隧道锚杆支护参数研究

Research on Rock Bolt Support Parameters of Tunnels in Gently Dipping Sandshale Stratum

砂岩页岩互层常为软硬相间的缓倾岩层,强度和变形各向异性显著,隧道支护结构受力机理复杂。以西延高铁武家塬隧道深埋段为研究对象,在现场地质调查的基础上,采用岩石破裂软件RFPA2D建立水平砂页岩互层隧道概化数值模型,分析锚杆长度和布置方式对围岩破裂特征的影响规律,提出合理的锚杆支护参数,通过现场监测验证支护参数的合理性。研究结果表明:(1)砂页岩缓倾地层各向异性显著,隧道开挖后在软岩层中产生剪切和张拉裂缝。施加喷锚支护后,可以有效抑制隧道拱顶软硬岩层间产生的剪切滑移和张拉裂缝。(2)随着锚杆长度的增加,围岩应力状态改善,破裂区形状由X形转化为洞周月牙形,破裂范围逐渐减小,声发射数减小,围岩稳定性提高。(3)随着锚杆分布范围由拱顶局部变为全周,围岩破裂区范围减小,最大主应力值减小,声发射数减小。(4)为发挥锚杆的组合梁加固效应,应与岩层呈现大角度相交布设,锚杆长度应大于软岩层厚度并深入硬岩层。

The interbedding of sandstone and shale is usually discovered as a gently dipping soft-hard rock stratum with significant anisotropy in strength and deformation,and the stress mechanism of tunnel support structure is complex.Taking a deep-buried section of Wujiayuan Tunnel on Xi'an-Yan'an HSR as the study object,based on on-site geological survey,this paper establishes a generalized numerical model of horizontal sandshale interbedded tunnel by rock fracture software RFPA2D,analyzes the influence law of rock bolt length and arrangement mode on surrounding rock fracture characteristics,puts forward reasonable rock bolt support parameters,and verifies the rationality of support parameters through on-site monitoring.The study results show that:(1)The anisotropy of gently dipping sandshale stratum is significant,and shear and tension cracks are generated in soft rock stratum after tunnel excavation.After the shotcrete bolt lining is applied,the shear slips and tension cracks between soft and hard rock strata at the tunnel arch crown can be effectively suppressed.(2)With the increase of rock bolt length,the stress status of surrounding rock is improved,and the shape of fracture zone is changed from X-shape to crescent shape around the tunnel.The fracture range is gradually decreased,the acoustic emission number is decreased,and the stability of surrounding rock is improved.(3)With the distribution range of rock bolts changing from local arch crown to full circumference,the range of surrounding rock fracture zone is decreased,the maximum principal stress value is decreased,and the acoustic emission number is decreased.(4)In order to give full play to the reinforcement effect of composite beam of rock bolt,it shall be arranged at a large angle with the rock stratum.The length of rock bolt shall be greater than the thickness of soft rock stratum and penetrate into hard rock stratum.