巨型地下洞室脆性围岩高应力破裂防治措施研究

脆性岩体高应力破裂是西部水电地下工程面临的主要岩石力学问题之一。依托世界最大规模的白鹤滩地下厂房洞室群,在概括高应力条件和玄武岩脆性特征基础上,说明了地下洞室围岩破裂破坏形式。采用3DEC中围岩能量释放等指标,研究了洞群布置、体形优化等宏观策略;依据围岩高应力集中特征,分析了开挖程序和支护时机等应对措施。结果表明,针对构造应力占主导的地下工程,可研设计应尽可能使主要洞室轴线与σ⁰₁小角度相交、宜选择双向成拱的圆筒形体形、保证顶拱曲率与应力拱相适应,并且,在施工期应尽可能沿σ⁰₁方向优先开挖、对应力集中的顶拱开挖不宜过多分幅、河谷应力条件下应优先开挖临江侧,此外,必须充分利用掌子面效应及时支护,抑制脆性岩体破裂扩展和时效变形。工程实践表明,防治脆性围岩高应力破裂的战略性措施能够降低洞室群围岩产生破裂破坏的总体风险,而战术性措施能够减小支护代价,提升工程安全性和经济合理性。

Study on the Prevention and Control Measures of High Stress Fracture in the Brittle Surrounding Rock of the Giant Underground Cavern

The high stress inducing fracture of brittle rock mass is one of the major rock mechanics problems in western hydropower project. Relying on the world’s largest underground powerhouse caverns, on the basis of the high in-situ stress condition and the brittle characteristics of basalt, the fracture failure mode of the caverns is explained. Using the index of energy release of surrounding rock in 3DEC, the macro strategies such as caverns layout and shape optimization were studied. According to the characteristics of high stress concentration in surrounding rock, the countermeasures of excavation procedure and supporting time were analyzed. Results show that for the underground engineering affected by high tectonic stress, in the feasibility study phase, the main caverns axis should be as far as possible intersects with σ⁰₁ at small angle, the cylindrical shape with the bidirectional arch should be adopted, and the curvature of the crown should be suitable to the stress arch. Moreover, in the construction period, the priority excavation direction should be along σ⁰₁, the excavate steps of arch with stress concentration should not be too much, and the river side of tunnel with river valley stress conditions should be priority excavated. In addition, it is necessary to make full use of the tunnel face effect to support timely and restrain the fracture extension and time-depend deformation of brittle rock mass. Engineering practice shows the strategic measures to prevent the high stress rupture of brittle rock can reduce the overall risk of the surrounding rock in the cavern, and tactical measures can reduce support cost, and improve construction safety and economic rationality.