Development and Verification of Applicability of a Borehole Meter using Laser Displacement Sensor

Abstract

A borehole meter with a built-in laser displacement sensor has been developed for measurements of stress change and deformation in rock. The fundamental principle of the instrument is to rotate the laser displacement sensor sequentially around a borehole axis and measure the distance from the borehole center to the wall of the borehole for each rotation angle. It has the following features:
1. Measurements can be made without contact way and its principle of measurement is simple.
2. Resolution is high and the range of measurement is wide.
3. Reliability is high because of many measuring points.
4. The geometry of cross-sectional plane in a borehole can be evaluated.
5. Measurements can be made at different depths in the borehole.
The applicability of a borehole meter was investigated through the laboratory tests in the block models with a broken zone or a discontinuity around a borehole.
As a result, the borehole meter was found to be available to the measurement in a situation where the broken zone or discontinuity exists. This means that the versatile monitoring can be performed at any depth of a single borehole in-situ rock mass with only one borehole meter.