An Engineering Failure Criterion For Rockfill Available to Purchase

On the basis of available triaxial test results for a variety of rockFills, a two parameter (B& a) failure criterion is proposed. B, which is a measure of equivalent structural strength of a rockfill is related to a particle breakage index defined at a confining stress of 1 MPa. A constant value of α- 0.85 is indicated. It is proposed to classify rockfills on the basis of B parameter and particle crushing index. Variation of angle of shearing resistance Φ with a normal effective stress σ_n is predicted and compared with those proposed by Leps (1970) and Barton &: Kjaernsli (1981).

Auf der Grundlage von dreiaxialen versuchsergebnissen fuer verschiedene steinfuellungen wird ein Bruchkriterium mit zwei Parametern (B & a) entwickelt. Es wird vorgeschlagen, steinfuellungen naph dem Parameter B und dem Partikelbruchindex zu klassifizieren. Eine Änderung.des Scherfestigkeitswinkels Ø mit einer effektiven Normalspannung σ wird vorhergesagt und mit den von Leps (1970) und Barton & Kjaernsli (1981) vorgeschlagenem verglichen.

Base sur les resultats des essais triaxials pour des remplissages differents de roche, une critere de rupture avec; deux paramlltres, (B & a) est developpe. Une Classification des remplissages de roche d"apres le parametre B et l"index de rupture de particule est propossee. Une variation de l"angle de resistance au cisaillement" Ø avec une contrainte normale effective σ est predite et comparee avec celle proposee par Leps (1970) et Barton & Kjaernsli (1981)

Engineering failure criteria for intact rocks (Fairhurst, 1964; Murrell,1965; Hoek, 1968; Bieniawski. 1974) and rockmasses (Hoek & Brown. 1980 and Yudhbir et el., 1983) have been developed to enable engineers to estimate failure envelope for both hard and soft rocks, and rock masses. Influence of degree of jointing and disintegration has been handled through unconfined compressive strength of intact rock, and rock mass rating" indices such as Q or RMR values. On the other end of spectrum of geological materials considerable progress has been made through experimental and theoretical investigations into the failure criteria for soils. Limitations of laboratory testing procedures to simulate gradation of rockfills (especially particle size) and deformation conditions in the field have resulted in much slower progress in the understanding of mechanisms of shear strength mobilization in rockfill and the formulation of a relevant failure criterion which takes into account their enhanced dilatant response at low stress levels and significant breakage of interparticle contacts with suppressed dilatancy at elevated stress levels during shearing.

Lee & Farhoomand (1967), Marachi (1969), Marsal (1973), Al Hussain (1983), Hardin (1985) and Rahim (1989) have shown that particle breakage increases with the maximum particle size. Rahim (1989) has demonstrated that particle breakage increases with increasing- d₅₀, grain uniformity, confining- stress and particle angularity. Marachi (l969) and Marsal (1973), have shown that angle of shearing resistance of rockfills is very strongly controlled by the amount of particle breakage. It would thus seem useful to best fit an empirical relationship to the experimental data to evolve a failure criterion for rockfill which takes into account the degree.