Abstract

The primary concern when constructing underground spaces for dumping and storing high-level radioactive waste deeper than 300 m in the earth, and when constructing tunnels for the Linear Chuo Shinkansen 1000 m below earth cover, is space destabilization due to high ground pressure or sudden water leakage. Therefore, it is necessary to take measures to assure construction safety and maintain the stability of the underground space for as long a time as possible. To achieve this, we built a new exploration, design, and construction system that can be used for evaluating the underground space more efficiently and effectively using a crack density diagram to calculate the rock bolt direction that will best intersect with cracks. In this paper, the authors show the specific content of this system and analyze the results of the evaluation in detail to verify their validity.

1. INTRODUCTION

The primary concern when constructing underground spaces for dumping and storing high-level radioactive waste deeper than 300 m in the earth, and when constructing tunnels for the Linear Chuo Shinkansen 1000 m below earth cover, is space destabilization due to high ground pressure or sudden water leakage. Therefore, it is necessary to take measures to assure construction safety and maintain the stability of the underground space for as long a time as possible. Furthermore, these structures should be sound and have a quality higher than is required in the construction of ordinary underground structures. Simultaneously, the reduction of construction costs is very important; this means that more efficient and effective designs and construction methods are required.

For this, the authors developed a grouting quality control system (Japanese patent publication number 2013-221298) to provide the best water stopping measures, which differ according to the geological features present, and applied it to the construction of a dam1) and examined the applicability to underground space construction.2) To provide the best water stopping measures possible according to the geological features, this system combines the use of (1) a crack density diagram to calculate the direction of the drilled injection holes that will best intersect with extant cracks and (2) a method to draw a contour plot of rock water channels based on the results of geostatistical analyses.

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