Strength at failure and modulus values for jointed rocks in unconfined and confined states were evaluated and stres-strain response was predicted which agreed reasonably well with the experimental response.
On a evalue la resistance à la rupture et les valeurs de module pour les roches a joints a ĺ et-al caplif et non-captif et on a predit la courbe de response contrainte-deformation qui correspondait raisonnablement bien avec la courbe de response experimentale.
Verhaltnissen warde Harte an Versaumnis-und Modulwerten fuer Verbundene Felsen in beengten und in unbeegten Zustandenberechnet und stress-spannungsreaktion Prophezeit, die sich im grossen und ganzen gut mit der experimentellen wirkung uebereinstimmte.
Rocks are seldom intact. The response of an intact specimen can range from that of a brittle material to that of a ductile material depending upon the combination of stresses and temperature. The rock mass is characterised by a macroscopic fabric pattern of joints/discontinuities rendering it into rather a massive rock or a heavily fractured mass. The mechanical properties of rock mass depend far more on its jointing system rather than on the strength of rock material itself. In fact, the joint frequency, the inclination of critical joint and the strength along this joint significantly control the elastic/plastic response and strength with respect to the applied stresses.
The simplest constitutive law used in engineering is linear such as Hook"s law which is valid only for a limited class of materials. Most materials are complex in nature and their response become nonlinear, which is predominant in materials that are influenced by factors such as state of stress, stress path, inherent or induced anisotropy and volume changes under shear. Rock mass is often one such material having complex stress-strain response. Tests on intact specimens revealed that the response not only depends on material composition of the rock rot also on the manner and environment in which the rock is tested. The stress-strain laws are also effected by micro-structure of rock material, confining pressure, rate of loading, size and shape of specimen, friction at the loading platens, temperature of rock, pore fluid and stress path or stress history. Thus, the stress-strain relationship is not unique for rock. Even for the same rock, different constitutive models maybe applicable under different conditions.
Miller (1965) suggested six modes of stress-strain responses in uniaxial compression for different formation of intact rocks; namely as elastic, elasto- Plastic, plastic-elastic, plastic-elastic-plastic, plastic-elastic-plastic with high compressibility and elastic-plastic-creep types. Often these shapes are idealised as shown in Fig. 1 to develop suitable constitutive relationships covering the following modes:
(Figure in full paper)
Elastic:
Linear isotropic or anisotropic
Non-linear-Hyperbolic or splines
Elasto-plastic: perfectly plastic, strain hardening/softening
Visco-elastic (creep): Maxwell, Kelvin and Burger"s models
Elasto-viscoplastic
Equivalent material model Conbines rock material and joint sets.
The hyperbolic model originally proposed by Kondner (1963) and developed further by Duncan and Chang (1970) is very simple, most general in nature and has physical significance.
