The additional resistant energy effect for supporting structure to surrounding rock in underground powerhouse
The supporting structure, composed of ordinary and pre-tensioned bolts, is generally adopted to reinforce surrounding rock in underground powerhouse. However, the reinforcement mechanism of surrounding rock under complex stress state is not yet fully understood, and it is difficult to quantitatively evaluate the reinforced effect. From a perspective of energy analysis, this paper studies the action mechanism of supporting structure. Firstly, it is defined that the additional resistant energy is an energy supply that supporting structure contributes to surrounding rock, and a theoretical analysis method of energy replenishment for supporting structure is proposed, together with its calculation formulas of resistant energy. Then, the side wall’s design parameters of 20 hydropower underground powerhouses in China are summarized. Finally, a concept of energy supporting index is put forward based on the additional resistant energy. The research result indicates that the additional resistant energy is composed of 3 parts: resistant energy provided by tensile strength of bolts, resistant energy provided by bonding effect of interface between bolts and surrounding rock, and resistant energy provided by bonding effect of fissure grouting in surrounding rock. Relationship between the additional resistant energy provided by bolts, the strength-stress ratio of surrounding rock, and the excavation span of main powerhouse is fitted by 4 empirical formulas. All energy supporting indexes of 20 projects are distributed in the vicinity of 1.0, this feature can provide reference for support design.