Abstract: The secondary lining formwork of the composite lining in superlarge underground engineering in hard rock has several disadvantages, such as difficulty in concreting, complicated formwork engineering, and excess concrete masonry work. Accordingly, a case study is conducted on an underground oil storage depot, and the finite difference calculation software and onsite insitu test are employed to analyze the mechanical mechanism and optimize the support system for largescale underground engineering. The results reveal the following: (1) When excavating a large underground cavern in the rock mass with good surrounding rock conditions, a singlelayer shotcrete lining can improve construction efficiency and reduce the amount of concrete under the premise of reasonable support parameters and guaranteed construction quality. (2) Compared with the 〖WT５《TNR#I》〗Q〖WT５《TNR》〗SYSTEM rock support table, the optimized support system of polypropylene fiber shotcrete support and prestressed bolt can better control the deformation of surrounding rock and reduce the tensile stress area of the support structure, achieving a support effect close to that of the composite lining. (3) After the field test, the deformation and stress of the optimized support system are acceptable, and the maximum deformation of the dome is approximately 8 mm, indicating a safe and reliable support structure.

Key words: underground engineering, superlarge cavern, hyperboloid dome, singlelayer lining, low prestressed bolt