高应力硬岩地区岩体结构对地下洞室围岩稳定的控制效应研究

STUDY OF INFLUENCE OF ROCK STRUCTURE ON SURROUNDING ROCK MASS STABILITY OF UNDERGROUND CAVERNS IN HARD ROCK REGION WITH HIGH GEOSTRESS

官地水电站地下厂房属典型的硬岩地区深埋大型地下洞室群,其重要特点是同时面临高地应力和结构面发育这2个不利条件,实测最大主应力为25～35 MPa,厂区无大的断层和软弱结构面,但错动带和裂隙十分发育。通过对地下洞室群施工过程中出现的围岩局部失稳破坏现象进行全面的分析整理,对三大洞室的岩体结构特征和围岩变形破坏模式进行系统的分析、比较和总结,从而对影响围岩稳定的两大控制因素——地应力和岩体结构对官地地下厂房洞室群围岩稳定的影响程度和方式进行分析和对比。研究表明,由于三大洞室围岩类别以II类为主,岩体结构以块状～次块状结构为主,围岩具有较高的力学强度和强度应力比,从而具有较强的抵抗应力破坏的能力;岩体结构对地下厂房围岩变形与稳定的控制作用较地应力则更为明显,地下洞室群开挖过程中出现的局部失稳或较大变形多与不利方位的结构面直接相关。三大洞室围岩岩体结构特征总体上的相似性非常明确,反映在三大洞室围岩的变形特征和破坏模式上具有很好的统一性。然而,三大洞室的岩体结构特征也存在一定的差异,导致岩体结构影响围岩稳定的方式和程度有所不同。结构面发育造成的另一个不利影响是为坚硬岩体在高地应力条件下产生卸荷时效变形提供了内部条件。因此,在强度应力比较高的硬岩地区,应充分重视岩体结构及其演化对围岩变形和稳定的控制效应。

Guandi underground powerhouse is typical deep cavern groups in hard rock region.The challenge is that the geostress in the powerhouse area is high and discontinuities are well developed at the same time.The major principal stress is 25–35 MPa,no regional fault or major weakness zone have been found,but shear zones and joints are well developed.Failure phenomenon of the surrounding rock mass during the excavation of the underground cavern groups has been reviewed thoroughly.Rock structures and failure modes of surrounding rock mass have been studied in full length.The influence of geostress and rock structure on the stability of surrounding rock mass have been investigated in detail.The results show that the rock masses are fresh and belong mainly to class II and have a relative high strength,and so a high strength-stress ratio.The surrounding rock masses has strong ability to resist stress-induced failure.The influence of rock structure on rock masses is relatively stronger than that of geostress.Local instabilities and large deformation of some locations are all controlled by adverse geological discontinuities.In general,the characteristics of the rock structures of machine hall,transformer chamber and surge chamber are similar.This results in the similarity of the deformation characteristics and failure modes of the surrounding rock masses.The three cavers have certain differences in rock structures.Rock structures have different influences on the surrounding rock masses in different caverns,and also the failure modes.Jointed hard rock may assume time-dependent deformation under high geostress and this is another adverse influence of rock structures on rock masses.So,in hard rock regions with high geostress where the strength-stress ratio is high and joints are well developed,the influence of rock structure on surrounding rock masses must be fully considered.