The Study on Volumetric Deformation of Rock

Dilatancy and fracture of rocks under uniaxial compression (1st Report)

Abstract

In this paper, volume changes of rocks under uniaxial compression were studies experimentally for three different types of rocks such as sandstone, tuff and mable. The stiff loading system by means of stiffening bar method were employed and the volume changes were directly measured by using an improved Bridgman's dilatometer so that it was possible to obtain stress-volumetric strain curves in pre-and post-failure regions of rock samples.
The main results in this study are summerized as follows;
(1) The three characteristic curves depending on rock types were found in this study. They are shown in Fig. 10.
(2) In order to characterize the dilatant properties of rock samples quantitatively, two factors, rev andσ_cr/σ_maxwere selected. The former is the volumetric strain at the dilatancy initiation, the latter is the stress ratio between the stress at the critical strain and the maximum stress at failure. These values on rock samples are summerized in table 1.
(3) The measurements of volume changes were also performed on dry and wet samples. For sandstone both the stress levels to initiate dilatancy and the failure strength were fairly lowered in wet samples compared with those in dry samples, but for marble, the difference between the two states was scarcely observed. In tuff, dilatancy hardening was not occured both in wet and dry samples, however, failure strength was reduced in wet state.