针对大型地下储油库施工期围岩安全控制问题,首先明确了洞室围岩失稳类型及表现形式,采用块体理论分析了结构面不利组合引发的块体识别及稳定问题,对施工期识别出的关键块体的几何形态进行了归类,并根据类别筛选需支护的关键块体。然后围绕施工期跨层块体(大型洞室多层开挖才能完全揭露)的识别、顺洞节理参与下的洞室围岩失稳特征、洞室交叉部位的潜在失稳风险等几个关键问题进行探析。研究结果表明:采用块体理论判别结构面不同组合能否形成关键块体并开展稳定与支护分析,是对依赖围岩质量分级进行支护设计这一传统做法的必要补充;结构控制型的硬岩洞段是洞库围岩稳定控制的关键,常表现为结构面切割下的局部块体失稳,块体的几何形态可分为“端正形”“扁平浅埋形”“尖长深嵌形”3类,需支护块体通常为“端正形”。跨层块体是高边墙洞室施工的主要危险源,需将多层开挖获得的地质素描图进行拼接比对,以分析结构面跨层延伸特征和交切情况,判识能否形成跨层块体;顺洞节理因其可见的延展出露有限以及“隐伏状”特点,可能因认识不足而引发块体失稳;洞室交叉部位的临空面增加,更少的结构面切割也可能形成致灾块体,从而增大安全风险。研究成果不仅深化了施工期洞室围岩块体识别分析的认知,还可为类似洞室工程围岩稳定性控制工作提供参考。

[Objective] The aim of this study is to address the issue of stability control of surrounding rocks during the construction of underground oil storage caverns. [Methods] We first clarified the types and manifestations of surrounding rock instability in caverns, and then applied the block theory to analyze the issues of block identification and stability caused by unfavorable combinations of structural planes. The key blocks identified during construction period were classified based on their geometric shapes, and key blocks requiring support were selected according to their morphological types. Subsequently, we focused on the identification of hazard-causing blocks during construction to analyze key issues such as the identification of cross-layer blocks (which only become fully exposed after multi-layer excavation in high-sidewall caverns), instability characteristics of surrounding rocks involving along-cavern joints, and potential instability risks at the intersections of caverns. [Results] Using block theory to determine whether different combinations of structural planes could form key blocks, followed by stability and support analysis, serves as a necessary supplement to the conventional approach relying on surrounding rock quality classification for support design. The geometric shapes of blocks were classified into three types: “regular-shaped”, “flat and shallow-buried”, and “sharp and deeply embedded”, with the “regular-shaped” blocks being the primary type requiring support. “Flat and shallow-buried” blocks were prone to spontaneous falling, “sharp and deeply embedded” blocks were less likely to become unstable, and “regular-shaped” blocks required support, thereby providing a basis for differentiated support during the construction period. Based on the distribution characteristics of blocks during the construction period, the key issues of the identification and control of hazard-causing blocks were summarized as follows: (1) cross-layer blocks were the main hazard sources during the construction of high-sidewall caverns. It was necessary to splice and compare geological sketches obtained from multiple excavation layers to analyze the cross-layer extension characteristics and intersections of structural planes to determine whether cross-layer blocks may form. (2) Along-cavern joints, due to their limited visible exposure and “concealed” characteristics, were prone to form collapse blocks when intersecting with other structural planes in hard rock sections, while in medium to soft rock sections, they may cause large-scale sliding instability. (3) At cavern intersections, the increase in free surfaces, along with fewer structural plane cuts, may still result in the formation of hazard-causing blocks, thereby increasing safety risks. [Conclusion] The findings advance the understanding of block identification and stability analysis during the construction of underground caverns. The proposed classification of block shapes and the summarized key issues in recognizing hazard-causing blocks can provide a reference for the stability control of surrounding rocks in similar cavern engineering projects.