Initial Stress Estimation by Use of Ultrasonic
Shoichi KOBAYASHI and Tohru YOSHIKAWA
Abstract:The present paper describes a new technique for estimating initial stresses in rock mass by measuring phase velocity of ultrasonic (elastic) waves in a specimen shaped from the bored core. The technique is supported by the following facts observed in the tests carried out for andesite, basalt, granite and sandstone specimens. 1) Phase velocities of both longitudinal and shear waves traveling in the perpendicular direction to the loading axis in the uniaxial compression test change considerably at the pre-experienced maximum stress. 2) The pre-experienced maximum stress is remembered at least one week. 3) The phase velocity of shear wave polarized in the perpendicular to the loading direction is not affected by the pre-existed stresses in other directions. Key Words:Initial stress, Ultrasonic waves, Phase velocity change, Memory of maximum stress, Multi-axial stress