A protective layer(PL) is commonly reserved above foundation surface to protect the underlying rock mass during dam foundation excavation. In China, the PL of dam foundation is conventionally subdivided into two or th...A protective layer(PL) is commonly reserved above foundation surface to protect the underlying rock mass during dam foundation excavation. In China, the PL of dam foundation is conventionally subdivided into two or three thin layers and excavated with the shallow-hole blasting method, even by pneumatic pick method in case of soft rock mass. The aforementioned layered excavation of the PL delays the construction of the whole project. After nearly 30-year practices, several safe and effcient methods for the PL excavation of dam foundation are gradually developed. They include shallow-hole bench blasting with cushion material(SBC) at the bottom of the hole, and horizontal smooth blasting(HSB). The PL is even cancelled on the condition that horizontal pre-split technique is employed during dam foundation excavation. This paper introduces the aforementioned two PL excavation methods(shallow-hole blasting and bench blasting) and horizontal pre-split technique of dam foundation without protective layer(HPP). The basic principles of blasting method, blasting geometry, charge structure, drill-and-blast parameters of typical projects are examined. Meanwhile, the merits and limitations of each method are compared. Engineering practices in China show that HSB is basically the optimal method for dam foundation PL excavation in terms of foundation damage control and rapid construction. Some new problems for dam foundation PL excavation arising, such as strong unloading and relaxation phenomenon that encountered in the gorge region of southwest China, are needed to be addressed; and the corresponding countermeasures are discussed as well.展开更多
基金supported by the National Science Fund for Distinguished Young Scholars of China(51125037)the National Key Basic Research Program(973 Program) of China(2011CB013501)+1 种基金the National Natural Science Foundation of China(51279135 and 51079111)the Doctoral Scientifc Fund Project of the Ministry of Education of China(20110141110026)
文摘A protective layer(PL) is commonly reserved above foundation surface to protect the underlying rock mass during dam foundation excavation. In China, the PL of dam foundation is conventionally subdivided into two or three thin layers and excavated with the shallow-hole blasting method, even by pneumatic pick method in case of soft rock mass. The aforementioned layered excavation of the PL delays the construction of the whole project. After nearly 30-year practices, several safe and effcient methods for the PL excavation of dam foundation are gradually developed. They include shallow-hole bench blasting with cushion material(SBC) at the bottom of the hole, and horizontal smooth blasting(HSB). The PL is even cancelled on the condition that horizontal pre-split technique is employed during dam foundation excavation. This paper introduces the aforementioned two PL excavation methods(shallow-hole blasting and bench blasting) and horizontal pre-split technique of dam foundation without protective layer(HPP). The basic principles of blasting method, blasting geometry, charge structure, drill-and-blast parameters of typical projects are examined. Meanwhile, the merits and limitations of each method are compared. Engineering practices in China show that HSB is basically the optimal method for dam foundation PL excavation in terms of foundation damage control and rapid construction. Some new problems for dam foundation PL excavation arising, such as strong unloading and relaxation phenomenon that encountered in the gorge region of southwest China, are needed to be addressed; and the corresponding countermeasures are discussed as well.
