穿断层破碎带隧道围岩大变形控制双梯度注浆机制

Mechanism of Double-Gradient Grouting for Large Deformation Control of Surrounding Rock in Tunnels Crossing Fault Fracture Zones

近些年,中国西部大量深埋隧道工程因关键线路控制无法避让一些活动性断裂,常常在跨越断裂带范围内出现围岩大变形破坏现象,例如侵限、偏压、塌方、底鼓等灾害,严重影响隧道工程施工和运营的安全可持续发展。为了控制断层破碎带隧道围岩大变形,隧道工程设计者和建设者采用了多种控制方案,例如超前注浆、多层钢拱架被动支护、锚杆索主动支护等,但是都因断层破碎带围岩强度过低而出现超前注浆诱发围岩拉裂破碎、主动支护锚杆锚固力不足等现象。为解决上述难题,首先,提出一种增强穿断层破碎带隧道围岩强度的双梯度注浆技术,建立双梯度注浆概念模型,构建3种双梯度注浆模式;然后,确定特定工况下注浆材料粒径梯度与注浆压力梯度的适配条件;最后,通过理论分析、物理模型试验和现场试验,探索双梯度注浆机制及其控制效果。研究结果表明:1)随着开挖步序的增加,穿断层破碎带隧道拱肩变形最大,构造应力对围岩稳定性影响较大。2)在双梯度注浆作用下,浆液扩散效果良好,围岩未出现大面积脱落破坏,隧道周围岩体应力分布均匀。3)双梯度注浆形成了坚硬交叉浆脉骨架,达到了应力补偿效果,将围岩变形量从原来的3 100 mm控制到278 mm以内,实现了“零换拱、零侵限、零突涌”的目标。

Numerous deep-buried tunnel projects in western China have failed to avoid some active faults due to key line control.Large deformation and damage phenomena of surrounding rocks,such as encroachment,offset pressure,collapse,and bottom failure,often occur across the fault zone,which seriously affect the safe and sustainable development of tunnel construction and operation.The risk of large deformation of the tunnel surrounding rock in the fault fracture zone can be controlled by adopting technical solutions such as advance grouting,multilayer steel arch passive support,and anchor cable active support.However,the low strength of the surrounding rock in the fracture zone contributed to the failure of advance grouting and active support anchoring.Therefore,the authors introduce a double-gradient grouting technology to enhance the strength of the surrounding rock of tunnels in the fault fracture zone,establish a double-gradient grouting conceptual model,and construct three double-gradient grouting modes to address the aforementioned problem.The adapting conditions of the grouting material particle size gradient and the grouting pressure gradient under specific working conditions are also determined.Finally,the double-gradient grouting mechanism and its control effect are explored through theoretical analysis,physical model tests,and field tests.Results show that the stability of surrounding rock is substantially affected by the tunnel arch shoulder and the structural stress with the increase in excavation sequence.Under the action of double-gradient grouting,the grout diffusion effect is good,the surrounding rock does not suffer large-scale detachment and damage,and the stress of the rock mass around the tunnel is evenly distributed.The double-gradient grouting forms a hard cross-grout vein skeleton,achieving a stress compensation effect and reducing the surrounding rock mass.The amount of rock deformation is controlled from the original 3100 mm to less than 278 mm,achieving the goals of"zero arch replacement,zero intrusion limit,and zero inrush",which establishes a theoretical and practical foundation for the control of large deformation of surrounding rock in similar tunnel projects.