Study On Damage Characteristics Of Large Underground Powerhouse Induced By Blasting Vibration

In the hydroelectric engineering construction, with more and more medium and large size hydraulic powerstation built in high mountain canyon district, the safety, economy and quick construction of large underground powerhouse seem to be more and more important. Drilling and blasting are still the main methods in modern underground powerhouse excavation. The coupling of blasting vibration and surrounding rock stress may result in the increase of surrounding rock deformation and relaxation of stress. Moreover, the blasting vibration may do harm to the latest shotcrete, rock-anchored beam, and the blasting excavation itself may damage the remaining rock mass. The blasting vibration and its damage effect to the remaining rock mass will have big influence on the safety of underground powerhouse construction and function. So the study of large underground powerhouse' damage characteristic under blasting vibration is important.Basing on the construction of Longtan and Dongfeng hydraulic powerstation, several methods such as the theories, the experiment, the number simulation and the field observation are used to study the damage characteristic of underground powerhouse under blasting vibration. Firstly, the construction procedure and characteristics of the large underground powerhouse are analyzed. Then with finite element program, the vibration respondence of underground powerhouse under blasting vibration is simulated. And then the blasting vibration attenuation rule and the blasting vibration effect to surrounding rock, to shotcrete ,to rock-anchored beams are studied. Moreover, the damage range of the blasting to remaining rock mass was analyzed. Finally, the blasting vibration control criterion of underground powerhouse is proposed. Through the study of the paper, several conclusions are drawn as follow:(1) Based on the method of dynamic FEM numeric simulation and the analyzed of the practical data, the distribution feature of particle vibration velocity along high sidewall is determined. The research indicates that the magnifying effect of particle peak vibration velocity along the high sidewall in underground excavation is not obvious. The empirical formula v = Kρ^αe^βH can be used to control and forecast the blasting vibration of the sidewall and the rock-anchored beams.(2) The infection of the blasting loads and excavation unloading loads to surrounding rock is studied, a conclusion was draw that the blasting loads which just have greater effect on the area close to the work area boundary ,the effect of blasting loads on the area that is 2m away from the boundary is smaller than that of the dynamic unloading of initial geostress which is similar to the blasting loads, for the rock which is certain distance away from the excavation outline, dynamic unloading of initial geostress is the main cause to the vibration of rock.(3) The response of rock-anchored beam under blasting vibration was researched, and the practical data was analyzed, then the response feature of rock-anchored under blasting vibration is determined and the blasting safety control criterion of rock-anchored is put forward. The bonding interface between rock-anchored beams and surrounding rock is the weakest place of the entire rock-anchored beam structure under blasting vibration. The effect of blasting vibration on rock-anchored beams may result in anchorage ability decrease, concrete intensity drop of the rock-anchored beams, rock-anchored beam concrete cracking, and bonding strength decrease between the rock-anchored beam and rock wall. The maximal horizontal tensile stress appears at top of the bonding interface, and the maximal vertical tensile stress appears at the top or the bottom of the bonding interface. 7cm/s can be adopted as the blasting safety control criterion of rock anchored which is older than 28 days.(4) The forecast method for damage zone induced by blasting excavation which is based on safety criterion by peak particle vibration velocity and the strength law of maximal tension stress is put forward, the damage zone induced by blasting excavation is confirmed. The enlarging excavation blasting of protective layer is the main reason to do damage to sidewall. Large decouple coefficient of charge should be used in the enlarging excavation blasting of protective layer. The damage zone of blasting usually just appears at the surface of the remaining rock mass. For smooth blasting, the incidence is about ten times of the borehole diameter.