Unexpected falls of tunnel face called “skin failures” remain one of the largest sources of injuries and fatalities in underground structures throughout the world. This feasibility assessment is being conducted as part of the mission to find ways to reduce hazards to worker populations.

A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the reflected laser beam frequency due to the motion of the surface.

One of the primary methods for analyzing tunnel face stability is the age-old method of “sounding” where a worker taps on the face and listens for the hollow sound of loose blocks of rock.

This paper experimentally investigates the feasibility of using noncontact laser-based vibration measurements to detect face fall hazards with the ultimate vision of improving, expanding and automating procedures for tunnel face inspection.

We connected four concrete blocks and arranged it to two lines and piled up three on each and made a tunnel face model of about 0.6 m in height 1.5 m in width. There were different joint conditions between concrete blocks to reflect loose block of rock in tunnel face.

Non-contact vibration measurements of the tunnel face model that had some types of loose blocks were carried out. The experimental results demonstrated that Laser Doppler vibrometry was considered to be a method for detecting anomalous vibrations in loose face rocks.

1. Introduction

Unexpected falls of tunnel face called “skin failures” remain one of the largest sources of injuries and fatalities in underground structures. This feasibility assessment is being conducted as part of the mission to find ways to reduce hazards to worker populations.

In tunnel construction, rock fall events at the cutting face, are particularly characteristic of the types of accident that occur. JNIOSH1) analyzed that it is clear that many of the labour accidents due to rock fall events happen when workers set off explosive charges or install steel arch supports in the cutting face during tunnel construction using the mountain tunneling method, especially NATM.

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2019. Japanese Society for Rock Mechanics. Permission to distribute - International Society for Rock Mechanics and Rock Engineering
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