ABSTRACT:

Blast-induced damage to the remaining rock mass can be caused both by the production blasting and the contour blasting itself. The optimum approach to contour blasting, the blasting excavation procedure, the criteria of blast-induced damage and reasonable blasting design parameters are presented and discussed in this paper. The application of two contour blasting methods (a) pre-split with a parallel free surface and Co) operational smooth blasting during the rock slopexcavation of the navigation structures at the Three Gorges Project are presented in detail.

INTRODUCTION

The high rock slopes of the Three Gorges Project are primarily located in the vicinity of the navigation structures. The navigation facilities of the Three Gorges Project are located on the left bank of the Yangtze River. They include the ship-lift and the permanent ship-lock as well as a temporary shiplock which is in operation during the period of construction. The ship-lift and the temporary ship-lock are located on the right slope of Tanzi Ridge. The total length of the temporary ship-lock line is 3950nt The main chamber. has a length of 300.Sm. Here, the maximum excavation height of the rock slope is about 140m. A middle rock pier with a total length of 350m, a width of about 30m and a vertical rock wall height of 36m remains between the main chambers of the ship-lift and the temporary ship-lock. The permanent navigation structures consisting of a double-line of five-step continuous ship-locks are located on the left slope of Tanzi Ridge. The permaneat ship-lock line has a total length of 6442m with a main chamber length of 1607m. There is also a middle rock pier with a width of 57m remaining between the main chambers of the double-line shiplocks. The height of vertical rock wall varies from 40 to 68m. The excavation height of the rock slope in the area of the permanent ship-lock varies from 100 to 170m.

The bedrock of the navigation structures is ?randiofire. Severalarge-scale dolerite and lamprophyre dykes are present The main faults strike northwest and are highly dipping. The main physical and mechanical properties for the granodiorite are given in Table 1.

Because of its great importance and complexity, assuring the stability of the high rock slope for the permment ship-lock has always been considered one of the key elements in the construction of the 'lluee

The loading due to blasting and the damage to the remaining rock are the important factors influencing the stability of the rock slope. Thus, during the excavation of the rock slopes for the navigation structures, the blasting vibration and damage must be carefully controlled The excavation work in the area of the temporary ship-lock and ship-lift began in April 1994 and continued through the end of 1996. Excavation of the permanent ship-lock began at same time and was successfully completed in November 1999.

In this paper, an optimized approach to contour blasting and the blasting excavation procedure, is presented and discussed. The application of some special contour blasting techniques during rock slope excavation in Three Gorges Project is presented in detail.

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