EXPERIMENTAL STUDY ON ISOTROPIC COMPRESSION DEFORMATION OF ROCKS AT
ROOM TEMPERATURE
*X. W. Zhang
Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines
Northeastern University, Shenyang, Liaoning China 110819
(*Corresponding author: zhangxiwei@mail.neu.edu.cn)
EXPERIMENTAL STUDY ON ISOTROPIC COMPRESSION DEFORMATION OF ROCKS AT
ROOM TEMPERATURE
ABSTRACT
The isotropic compression deformation data with increasing confining pressure for conventional triaxial
tests, in commonly was ignored, more attention focus on the strength improved results from an increasing
in confining pressure. High pressure (up to 100 MPa) isotropic compression tests were carried out on
marble, gneiss and sandstone specimens, of which represents the typical rocks, to investigate isotropic
compression deformation characterization. Experimental data with respect to volume change in loading
and unloading are presented. An apparent volume change inflection point (sensitive stress) was observed at
a lower pressure range for porous sandstone, indicating that the elastic-plastic behaviour arising in the
isotropic compression stage, similar with the anisotropic compression (such as triaxial shearing), but in
tight hard rock, the sensitive stress is much higher, or not probed prior to 100 MPa. The irrecoverable
volumetric strain in the unloading can be seen for sandstone as well. The anisotropic deformation was
discussed in accordance with the axial and radial deformation measurement. It was found that essential
features of mechanical anisotropy are the irreversible in deformation range. The deformation feature in the
isotropic compression tests is a very complex issue due to the factors concerning the stress history,
unloading in sampling and in-situ stress, suggesting to separate the individual factor so that a reliable
model production.
KEYWORDS
Isotropic compression, Bulk modulus, Volume change, Loading and unloading
Figure 1 –Confining pressure-volumetric strain curves for four type rocks in loading and unloading.