Abstract:

[Objective] Underground oil storage caverns are typically located in areas with hard crystalline rock, where the stability of surrounding rock mainly manifests as localized block instability. Traditional rock mass classification methods focus solely on analyzing and evaluating the overall stability of the surrounding rock, often neglecting the problem of block instability caused by unfavorable combinations of structural planes. [Methods] Block theory, utilizing geometric topological analysis to evaluate rock blocks formed by intersecting structural planes and their stability characteristics, serves as an effective approach for assessing the stability of underground caverns. Building on this block theory, this study utilized the whole-space stereographic projection method to identify removable blocks formed by the combinatorial intersection of various structural planes. The residual sliding force of these removable blocks was then used to determine whether they were key blocks requiring support. Subsequently, key blocks underwent maximum block morphology analysis to eliminate non-engineering-support blocks. Finally, positional block analysis was performed on blocks requiring support. [Results] This study developed a comprehensive flowchart for on-site block prediction analysis during engineering rock mass excavation. The specific analysis process was as follows. First, the development patterns of structural planes in the main cavern were analyzed and summarized based on geological mapping data obtained from preliminary surveys and the excavation of the main cavern’s top layer. Next, structural planes were combined, and the whole-space stereographic projection method was employed to identify potential removable blocks and key blocks that may form on the middle and lower sidewalls of the main cavern for each combination. Then, the geometric morphology of these key blocks was analyzed using their maximum block shape. Finally, blocks requiring support were identified based on their maximum block morphology, and corresponding support schemes were proposed. [Conclusion] The main conclusions are as follows: (1) through full-space stereographic projection analysis of various combinations of structural planes, the removable blocks and key blocks formed by these combinations on the left and right sidewalls were identified. (2) Based on the maximum block morphology of each key block, “shallow-buried” and “slender” types of non-support key blocks were eliminated, leaving only the “compact” type of blocks requiring support. (3) Support schemes were proposed based on the actual morphology of the identified “compact” blocks. The findings provide a theoretical foundation for the support design of cavern surrounding rock and hold significant value for broader applicability in rock underground engineering construction.

Key words: block theory, block prediction, stability of surrounding rock, whole-space stereographic projection, key blocks requiring support