Mitsutoshi Yoshimine

A Unified Strength criterion for rock material

Abstract A non-linear Unified Strength criterion for rock material is presented. It is the development of the Unified Strength Theory (in: M. Jono, T. Inoue (Eds.), Mechanical Behaviour of Materials-VI (ICM-6), Pergamon, Oxford, 1991, pp. 841–846) and the modification of the Hoek–Brown strength criterion (Underground Excavations in Rock, The Institution of Mining and Metallurgy, London, 1980). The effect of intermediate principal stress on rock strength is considered in the non-linear Unified Strength criterion. The Hoek–Brown criterion is a single-shear strength criterion that forms the lower bound, and the non-linear twin-shear strength criterion forms the upper bound in the deviatoric plane. All the failure criteria ranging from the Hoek–Brown criterion (lower bound) and the non-linear twin-shear criterion (upper bound) and a series of criteria ranging between these two bounds may be introduced by the non-linear Unified Strength criterion. The theory can also be generalized to rock mass strength.

EFFECTS OF ANISOTROPIC CONSOLIDATION AND INITIAL SHEAR LOAD ON LIQUEFACTION RESISTANCE OF SAND IN SIMPLE SHEAR CONDITION

Undrained triaxial test is commonly used in laboratory for evaluating liquefaction resistance of sand. The principal stress components are fixed vertical and horizontal in triaxial tests, thus it is impossible to examine the effects of initial consolidation stress ratio (Kc = σh / σv) and initial stress ratio (α = τ/σv) independently. This study utilized hollow cylindrical specimen and mutual effects of these two stress conditions are researched in detail. The outer and inner diameter of the hollow specimens were maintained constant during undrained cyclic loading to realize exact simple shear condition. It was found that the liquefaction resistance ratio to the initial vertical stress increased with increasing consolidation stress ratio (K c ) and initial stress ratio (α). It was also shown that the effect of initial stress ratio (α) was smaller for larger initial consolidation stress ratio (K c ).

Application of the Unified Strength Theory in Analyzing Fracture Strength

In practical engineering, the cracks are always mixed mode. The research on the mixed fracture criterion has an important significance in fracture mechanics and engineering. Stress state of the mixed mode cracks is complicated. A new unified strength theory considering the effects of all the three principal stresses is generalized into the fracture mechanics in this paper. The complex stress states are common characteristics between the mixed mode cracks and the unified strength theory. A unified fracture function criterion is established by using the unified strength theory in this paper. In the unified fracture function, the difference between tension and pressure and the effect of the intermediate principal stress σ2 are considered. With the variation of α = σt/ σc and failure parameter b , a series of mixed mode crack criteria are formed, and can be applied for many materials. The J-integral is calculated through FEM. According to the relation between the result and the stress intensity factor, Klc can be obtained. Then it is used in the unified fracture function. The unified fracture criterion is compared with those of other mixed mode criterions.