Evolution Mechanism Of Dynamic Rock Damage Induced By Blasting Excavation In Deep Valley Slopes

There are a large amount of hydraulic resources in alpine and gorge region of southwest China.The construction of hydropower projects in this area involves the large-scale blasting excavation of rock slopes in deep valley.When the rock slopes are excavated with drilling and blasting method,the remaining rock mass of the slope will inevitably be damaged by the blasting load,and the stability of the rock slope will be affected.Therefore,investigating the evolution mechanism of dynamic rock damage induced by blasting excavation in deep valley slopes is of great significance to the optimization design and safety evaluation of rock slopes blasting excavation in hydropower projects.This dissertation focus on the evolution and control of dynamic rock damage induced by blasting excavation in deep valley slopes.And a series of related studies are conducted with methods of theoretical analysis,numerical calculations and filed test data analysis.The damage mechanism of rock under blasting load,the evolution process of dynamic rock damage with different blasting excavation method,and the PPV criterion of rock blasting damage were studied.The main research contents and conclusions are concluded as follows.(1)Based on theoretical analysis of explosive mechanics and LS-DYNA dynamic finite element numerical calculations,the blasting load history curve on the borehole wall during rock blasting excavation and the spatiotemporal evolution of stress wave in single cylindrical hole blasting of rock mass were determined,and the mechanism of rock dynamic damage induced by blasting was investigated.The huge impact load at the moment of explosive initiation in the blasthole will causes compression and shear damage within a certain range of the vicinity of the blasthole in the rock mass,in the decay process of blasting load,the tangential and radial tensile stress around the blastholes will causes tensile rock damage outside the compression and shear damage zone.(2)The evolution process of dynamic rock damage in rock slope are investigated with method of numerical calculation,which induced by two different contour control blasting method of pre-splitting blasting and smooth blasting.Research indicates that the damage of remaining rock mass excavated with pre-splitting blasting method is mainly induced by detonation of pre-splitting holes,while excavated with smooth blasting method it is the cumulative effect by detonation of all blastholes.The blasting damage effects on remaining rock mass induced by detonation of pre-splitting holes are greater than smooth holes.The effects of the initial high in-situ stress conditions on rock blasting damage in deep valley rock slopes are explored,the initial in-situ stress causes compressive stress concentration around the blastholes and limit the development of rock tensile damage,initial high in-situ stress can inhibit the rock blasting damage.The cumulative damage effects of repeated disturbances of different rock benches blasting excavation on remaining rock are also investigated,the repeated disturbances of different contour holes blasting on rock mass in slope berms are obvious.(3)Based on numerical simulation and field test data,the relationship between the blasting damage depth of the slope rock mass and the vibration of rock in the upper berms was studied.The results show that the vertical blasting velocity of rock in the upper berm is the largest,but the vertical velocity is not directly related to the blasting damage depth of the slope rock mass.The tangential blasting vibration can reflect the damage depth of remaining rock mass,it is more appropriate to select the tangential vibration as the blasting safety criterion.In addition,the smaller the rock benches height,the greater the rock blasting vibration on the upper berms.So the effects of slope benches height should be considered in the safety control standards for slope blasting damage.(4)Based on the filed test data of blasting vibration monitoring and sound wave detection of rock mass,the blasting vibration amplitude and blasting damage range of remaining rock mass during blasting excavation of the rock slope on the left arch groove of Baihetan Hydropower Station are analyzed and evaluated.The function relationship between the peak particles vibration(PPV)and the rock blasting damage depth was established by the regression analysis,and the PPV threshold for slope blasting damage control was given out.When the blasting damage depth of the rock mass is limited to 1.0m,the maximum tangential vibration velocity of the rock mass at a blast center distance of 15?20m is 6.0?9.0 cm/s.