ABSTRACT

The earth and rock excavation volume of the permanent shiplock accounts for 40 percent of the total of the whole Three Gorges project (TGP). The supplementary study of the excavation technique is quite systematic and comprehensive. The finishing excavation technique adopted for the vertical walls including the millisecond blasting technique between deep holes and the twice buffer blasting plus twice smooth blasting combined with comprehensive trench blasting technique with non-electric initiating connection and soft padding arrangement at bottom of holes are more reliable and much safer compared with the excavation mode such as with pre-split blasting to excavate at one go or other modes. This technology is able to satisfy the requirements of construction quality and construction progress, successfully facing the challenge of the excavation of the world-class high vertical slopes of the permanent navigation lock.

1 INTRODUCTION

The Three Gorges navigation lock is one of the three major components of theThree Gorges project, representing a "super class" navigation structure in the world. It has a gigantic construction scale, very complicated topographical and geological conditions and tight construction time schedule. It also requires the use of high-level technologies and adoption of complex construction procedures. Its earth and rock excavation volume accounts for 40 percent of the total of the whole Three Gorges project (TGP). The permanent navigation lock is located on the left bank of the Yangtze River (Fig 1). The lock wall is much different with a conventional man-made steep high slope. Because the four long vertical walls of the double-lane two-way lock chambers are excavated vertically into very deep rock mass, with strongly influenced by relaxing of geostatic stress in such a large area, there are no any precedent in theoretical research and construction practice both at home and abroad for the man-made high rock slope as such.

2 STUDY AND APPLICATION OF CONTROLLED BLASTING TECHNIQUE

The main features and difficulties in construction summed up as the following.

  1. Complex geological conditions.

  2. Complexity of the navigation lock structure and much sensitive reaction to the geological conditions.

  3. High requirement of vertical wall finishing technique with strict control of slope deformation.

  4. Huge volume of rock excavation, but tight construction time schedule.

  5. Great risk in safety during construction.

Many studies are processed to insure the construction success.

2.1 Two-times smooth (pre-split) blasting plustwo-times buffer blasting for navigationlock trench excavation

Through conducting site testing of ordinary millisecond blasting method for benching blasting by drilling deep holes. It is found that: The scope and depth influenced by blasting on the preserved rock mass at lateral side and in the direction of back wave are quite big, especially surface layer of the rock mass is badly damaged with cracking by pulling force.

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