断层破碎带隧道结构破坏离散元数值试验

Discrete element numerical test of tunnel structure failure in fault fracture zones

为研究次生断裂的形成原因、隧道结构破坏特征及其机理。以福宜高速公路梁王山隧道为依托,采用MatDEM离散元结合现场测试的方法,模拟断层运动和隧道破坏。结果表明:受主断层两侧地层相向运动影响,在离FW4断层出口远端软弱地层产生了次生断裂,隧道开挖后围岩次生裂隙扩展并发生不均匀破坏,表现为拱顶开裂,边墙强烈内挤和纵向裂缝等;低刚度裂缝能吸收变形产生明显变形阻断作用,但却容易引起对向侧部围岩的进一步应力集中,加剧隧道的不均匀破坏;为避免受次生断裂影响下穿越断层破碎带隧道发生破坏,应对次生裂缝或节理进行注浆加固,减少新生裂缝数量,削弱附近围岩的应力-变形集中,降低隧道施工风险。

[Objective]To elucidate the complexity of secondary fractures,the fundamental mechanism for the gradual failure of the tunnel structure is explored.[Methods]The MatDEM discrete element method was employed to investigate the Liangwangshan tunnel on the Fuyi highway in Yunnan province.The geological conditions at the tunnel site were complex,characterized by karst formations and intersecting fault fracture zones.During tunnel excavation near the FW4 fault fracture zone,frequent disasters including initial support cracking occurred.Therefore,the failure mechanisms of tunnels passing through fault fracture zones must be explored.[Results]Findings provide guidance on the genesis and propagation patterns of secondary faults near the tunnel.Notably,these faults tended to develop within strata characterized by inherently weak geological compositions situated at a considerable distance from the exit point of the F4 fault zone.The spatial distribution of faults was due to the lateral displacement in the strata,flanking the primary fault line and imposing notable stress and strain on the surrounding rock mass.Consequently,secondary faults emerged as tangible manifestations of the intricate geological interactions at the site.As tunnel excavation progressed,the latent influence exerted by these secondary faults gradually became increasingly obvious.Moreover,the excavation process accelerated the generation of secondary faults,activating dormant faults and causing fissures to form within the surrounding rock.The resultant structural anomalies,ranging from primary cracks and fissures to pronounced inward compression of sidewalls and the propagation of longitudinal rifts,posed formidable challenges to the overall structural integrity and stability of the tunnel,considering it traversed unfavorable geological conditions.Based on observations of low-stiffness cracks near the tunnel,these cracks exhibited distinctive behavioral traits and a remarkable capacity to absorb deformations,producing considerable deformation-blocking effects.However,they could increase stress concentration in the surrounding rock on the opposite side,exacerbating uneven tunnel failure.In such a case,the groundwater in the tunnel was not affected.However,excessive cracks could create seepage channels and cause engineering disasters in water-rich areas,such as water influx into the tunnel,substantially affecting tunnel safety.Considering the structural damage in tunnels crossing fault and fractured zones,reinforcing the support structure is essential to prevent the damage caused by secondary fractures influencing the tunnel.One of the most commonly employed reinforcing methods is grouting reinforcement,which enhances the stiffness and strength of the support structure.This approach helps reduce uneven stress on the tunnel and mitigates the formation of numerous new cracks.[Conclusions]Low-stiffness cracks can absorb deformation and block deformations;however,they can lead to increased stress concentration in the surrounding rock on the opposite side,exacerbating uneven tunnel failure.Grouting reinforcement effectively reduces uneven stress on the tunnel.The results provide valuable insights for similar projects.