Improved design and data interpretation of a multi-purpose borehole testing device for soft rock

Abstract

The authors previously developed a multi-purpose borehole testing device (BTD). The purpose of the BTD was designed for obtaining mechanical properties including anisotropic elastic modulus and interface shear strength properties for soft rock that may be easily disturbed during sampling. Since the creation of the previous BTD, a few minor problems were experienced during in situ testing operation. In the present work, improvements both in equipment design and data interpretation were made. Improved design of BTD successfully reduced the chance for pressure meter test (PMT) membrane breakage, allowed larger expansion of borehole jack test (BJT), improved the waterproof of the bottom compartment and made easy for the whole equipment setup. The refined design has improved the in situ performance of BTD. New approach of data interpretation was also proposed. A series of BTD tests, including BJTs, borehole plate loading tests and borehole shear tests were carried out to demonstrate the capability of the refined borehole test device.