Study On Blasting Seismic Effects Of Cable Shaft In Xi LuoDu Hydropower Station

The most common method used in shaft excavation was still drilling and blasting. Fracturing of rock and concrete materials under blasting impact was a very important issue. Concrete lining and rock around of the shaft was subjected to negative impact while complete the excavation of the shaft. The cement surface of rock and concrete may separated and the strength of concrete may decreased under blasting vibration effect, and the lining effect may drop or even useless. The concrete lining would peel off under blasting wave. The damage of surrounding rock and the original fracture run through and the generation and expansion of the new fracture may lead to the deterioration of mechanical properties. When the blasting vibration reaches certain intensity, it may lead to shaft wall rock or concrete lining which was at critical stress state partially collapse or instability, even lead to the occurrence of accidents.By field test on cable shaft of Xiluodu Hydropower Station, Regression analysis according to Sadaovsky empirical formula were using. The seismic wave propagation attenuation was obtained. Use the attenuation formula to forecast the vibration velocity of the highest measured point. Compare the Predicted value with the measured data, Result have shown that there is elevation amplification in shaft blasting vibration. The Magnification factor of Horizontal direction was 1.49～2.24,and the vertical direction was 1.78～2.73. The greater of the relative height, the magnification factor is larger. It was obvious of the blasting vibration wave amplification effects with elevation increase. Blasting vibration velocity is also subject to attenuation effects, the interaction between the two, blasting vibration velocity amplification factor increased with the increase of elevation, as to a certain critical value, the attenuation factor accounting for the main factor, the magnification factor no longer increases with elevation. With Sadaovsky empirical formula amended, attenuation formula was got which consider of the elevation factors, the linear relationship of corrected formula was significantly. It can predict blasting vibration velocity which has elevation amplification factor. The maximum security section of quantity of explosive was obtained according to corrected formula, and then re-optimizing the design of the blasting network, reducing blasting vibration effect.Dynamic FEM was used to simulate the blasting effect of the shaft. Shaft structures respond to the action of the blasting seismic wave was analyzed. The regression results were compared with the simulation results. Studies have shown that the numerical simulation results trends was fit with the regression trends when the relative height difference is not significant. The vibration velocity was attenuating fast between 0～15 meters, more than 60% of overall vibration velocity was attenuated. Less than 10% of overall vibration velocity was attenuated at 30 meters out of the blasting center. Strength failure criterion was used to check the stability of the shaft, and a reference for the safety of the following construction was provided.