Development and consideration on excavation technology of protection layers of foundation rock for hydraulic structure

Technologies for excavating protection layers of foundation rock of large and medium sized hydropower stations under construction in China are developing rapidly. In order to improve methods for excavating protection layer of foundation rock and simplify blasting procedures, the one time blasting technology for excavating foundation rock protection layer has been listed as a key research subject. At present, there are following ways for the experimental study and application of one time blasting technologies for excavating protection layers of foundation rock of hydropower stations in China:① small bench millisecond delay blasting with a soft cushion provided in the bottom of vertical holes;② horizontal presplit blasting together with short delay blasting between vertical holes or rows of holes; ③ horizontal hole smooth blasting together with horizontal hole bench blasting;④ smooth blasting together with cushion holes for excavating most of lateral protection layers. Through continuous efforts, the one time blasting technologies for excavating foundation rock protection layers have been successful and have found application, but how to achieve a best combination of technology with economy is still a subject to be extensively investigated.