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To recommend the excavation procedures and design parameters for underground powerhouses, excavation procedures of fifty-one underground powerhouses in China were summarized and analyzed based on in situ stress conditions. Firstly, the complex stress environment in China was introduced and fifty-one underground powerhouses with their engineering scale, size, lithology, rock classification and in situ stress level were listed in detail. Subsequently, to evaluate the influence of in situ stress levels on excavation procedure design, the correlation between excavation procedures and in situ stress level in three main excavation zones were analyzed accordingly. Moreover, to provide the excavation design recommendations, the strength–stress ratio (SSR) was promoted to analyze and recommend the design parameters, and the blasting excavation design based on the stress transient unloading control was also supplemented. The results show that excavation procedures have different priorities under different in situ stress levels, and the design parameters show an obvious relationship with in situ stress levels. Moreover, the excavation procedure parameters are suggested to adjust accordingly under different SSR. The discussion of influencing factors and specification ensures its rationality and accuracy. It is believed that the summary and recommendations can provide a good reference for excavation procedure optimization of underground powerhouse under high in situ stress. [ABSTRACT FROM AUTHOR]

• Using new numerical simulation method (FDEM) and theoretical analysis on smooth blasting research. • Investigating the influence of in-situ stress, hole spacing, and radial decoupling coefficient on the superposition of blasting stress and the cracking characteristic between holes. • Proposing the design of smooth blasting parameters considering the influence of in-situ stress and verify it based on specific project. Smooth blasting is an important excavation method in tunnel construction, creating a smooth and even excavation profile during the excavation process. In this study, the influence of in-situ stress, hole spacing, and radial decoupling coefficient on the superposition of blasting stress and the cracking characteristic between holes were investigated by using integrated analytical and numerical analyses (FDEM). Based on those results, the design of smooth blasting parameters considering the influence of in-situ stress were suggested, and verified against the data collected during the blasting excavation of diversion tunnel at Jinping II hydropower station. The results indicated that the propagation of blast-induced fractures are significantly influenced by the insitu stress conditions, tending to extend towards the direction of the maximum principal stress thus the holes should be arranged along the direction of the maximum principal stress to ensure the formation of cracks between holes and smooth excavation of the wall. [ABSTRACT FROM AUTHOR]

• New face destress blasting design concept and theoretical analysis. • Energy release and damage characteristics induced by fracture planes under high in-situ stress. • Experiments on rock mass damage induced by single and double fracture surface. During the excavation of the deep tunnel development face, the rock burst will abruptly occur with the instantaneous release of strain energy stored in the rock mass. Face destress blasting as the preconditioning method to fracture the rock mass, release the accumulated strain energy ahead of development face in advance, is considered one of the tactical approaches to reduce the rock burst proneness. However, the challenge of conventional destress blasting is how to effectively fracture rock under high in-situ stress and reduce strain energy accumulation. Therefore, in order to effectively release energy, a new destress blasting design utilizing fracture planes is proposed. First, blasting holes parallel to the maximum principal stress are employed to generate fracture planes. Next, fracture surfaces are used to reflect stress waves to enhance rock damage, so that the rock mass can be fractured by making full use of the explosive energy, and the accumulated energy can be released effectively. In this study, the failure mechanism of the rock mass is first theoretically investigated, and then the reliability of the rock fracture and energy release was validated by combining numerical simulation with experiments. The results demonstrated that this approach can more effectively achieve energy release and fragmentation during destress blasting. [ABSTRACT FROM AUTHOR]