On the basis of the theoretical analysis of the blast induced damage in the remaining rock mass, questions such as the optimization of contour blasting method and blasting excavation procedure during rock slope excavation are studied and discussed in this paper, and a case application of an special contour blasting method, i.e. pre-split with a lateral free surface, during the rock slope excavation at the Three Gorges Project, is also presented In detail.
The navigation facilities of the Three Gorges Project, including the ship lift and the permanent ship lock, are arranged on the left bank of Yangtze River, and a temporary ship lock is arranged during the period of construction. The maximum excavation height of the rock slope in the area of the ship lift and the temporary ship lock is 140 meters, and there is a middle rock pier, with a total length of 350 meters, a width of about 30 meters and a height of 36 meters, remained between the main chambers of the ship lift and the temporary ship lock. There is also a middle rock pier with a width of 57 meters and a height from 40 to 68 meters remained between the main chambers of the double-line permanent ship locks, where the excavation height or rock slope is from 100 to 170 meters. The bedrock of navigation structures is granite diorite, and there are several large-scale dolerite & lamprophyre dynes presented, main faults strike in northwestern direction & are highly dipping. Because of its great importance and complexity, assuring the stability of the high rock slope of the permanent ship lock during both construction and running period has been considered all the time as one of the key technologies of the construction of the Three Gorges Project. The blast induced damage to the remaining rock can be one of the main factors influencing the stability of rock slope. So, during the excavation of the rock slope of the navigation facilities, the control of the blast induced damage is considered as one of the important technological measures to ensure the quality of the excavation of the slope. The excavation in the area of the temporary ship lock and the ship lift began in April 1994 and continued through the end of 1996, while the excavation in permanent ship lock began at same time and was successfully completed in November 1999. In this paper, the optimum approach of the contour blasting method and blasting excavation procedure during rock slope excavation are studied and discussed, and case of the application of an special contour blasting method, i.e, pre-split with a lateral free surface, during the rock slope excavation at the Three Gorges Project, is presented in detail in the end of this paper.
During the procedure of rock fragmentation by blasting, under the action of blast loading, while the rock mass is broken into fragments, a blast induced damage zone occurs near the surface.
