Abstract

The authors developed a system for predicting geological conditions not just of excavated areas but also ahead of the tunnel face by processing drilling data using Ordinary kriging, a geostatistical approach, and by visualizing conditions in real time. Using auto-controlled face drilling rigs, the authors confirmed the easy and rapid acquisition of drilling data from blast holes and rock bolt holes, along with three-dimensional coordinates.

The authors deployed the system in real time to decide whether pre-supports such as forepoling and facebolts would be necessary for a strongly sheared slate area at tunnel faces of the Shin-Kuzakai Tunnel (provisional name). The prediction provided information essential for decisions on construction methods. It also enabled safe streamlining of the process of deploying pre-supports. The authors also compared the applied support systems with P-wave velocity distributions of the rock mass derived from specific energy of drilling and rock mass classification distributions.

1.
Introduction

Choosing appropriate support systems and pre-supports are the key to ensuring quality, stability, and safety in tunnel construction projects. Typically, the tunnel face is observed during the excavation to evaluate geological conditions. The tunnel face is generally observed once a day, while excavations usually occur around four times a day. This means changes in geological conditions may be overlooked. In addition, as demonstrated by past incidents, the presence of a weak layer behind a tunnel face or a side wall may result in the collapse or significant deformation of a tunnel face or wall.

With respect to the geological conditions behind a side wall, hardness is determined empirically from drilling data for rock bolt holes. However, acquiring and analyzing this data requires a great deal of time and labor. Obtaining information on geological conditions that would allow real-time decisions on construction plans tends to pose extreme difficulties.

Using auto-controlled face drilling rigs whose use is increasingly common, we found a way to quickly and easily acquire drilling data from blast and rock bolt holes. We established a system that predicts geological conditions not just in excavated areas, but ahead of the tunnel face; this method visualizes conditions in real time by processing drilling data based on a geostatistical approach called Ordinary kriging. We applied this system to the construction site for the Shin-Kuzakai Tunnel (provisional name) on the Miyako-Morioka Cross Road and confirmed that the system provides essential information for construction plan decisions.

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