Generalized Relaxation Behaviour of Rock under Uniaxial Compression

Abstract

In Practice, rock mass is neither subjected to pure creep or pure relaxation but to a force-displacement condition dictated by surrounding rock. But few are available in the literature about this problem.

Generalized relaxation test of Sanjome-andesite and Kawazu-tuff was conducted under uniaxial condition. The generalized relaxation test investigates the property of time-dependent decrease (or increase) of stress under increasing (or decreasing) strain. Concretely, the increment of force-displacement relation was kept as follows;

ΔF_{R} - γ k_{R} ΔY_{R}＝０

Where ΔF_{R} is the increment of force, ΔY_{R} is that of displacement,
k_{R} is the
stiffness of rock sample in the elastic region and γ is the direction factor of
relaxation. Considering all possible boundary conditions (the relationship of
the stress-strain), the direction factor of relaxation can be all real number.

By plotting all results on a stress-strain diagram, it can be said that the stress-strain curve shrinks as time goes by. In other word, rock characteristic line changes with the lapse of time.

A strain rate at an arbitrary time in the region where the strain rate is signified by a continuous increase is inversely proportional to the time up to final failure. If this law is applied to rock mass, the failure of underground constructions may be predicted.

KEY WORDS: Rock, Creep, Relaxation, Uniaxial Compression, Stress-Strain Curve