A brittle rock-like material having a wide range of porosity and density, and a medium range of strength has been developed. The compressive strength and tensile strength decreased exponentially with an increase in the porosity under both dry and water saturated conditions. Percentage reduction in strengths due to water saturation increased with an increase in the porosity. The density had an opposite effect on the properties.


Un materiau fragile et de caractère rocheux avee de fortes variations de porosite et densite et une variation moins importante de resistance a ete cre. Les resistances de cc materiau en extension et en compression decroissent exponentiellement par rapport au porosite, quel que soit le contenu d'eau. Le plus grand le porosite, la plus importantes sont les abaissements de resistances dûes à la presence d'eau. Par contre, une hausse de densite donne lieu à une amelioration des resistances.


Es wurde ein Material mit großer Porositat und Diehte und einer mittleren Zerreißfestigkeit entwickelt. Die Druck- und Zugbelastbarkeit fallt exponentiell fuer einen Anstieg in der Porositat, sowohl unter trockenen Bedingungen als auch bei Wassersattigung. Eine prozentuale Reduktion der Zerreißfestigkeit wird durch einen Anstieg in der Porositat verursacht, wahrend ein Anstieg der Diehte den gegenteiligen Effekt hat.


Porosity and density are two important indicators of strength of rocks, particularly sedimentary rocks. For example, differences in mechanical properties of sandstones and shales from various formations are largely due to differences in porosity and density. For identifying the effect of porosity and density on the strength of rock, it was necessary first to develop a brittle rock-like material which has similar behaviour and strength as a medium-strength rock. The developed rock-like material can also be used for other purposes. Many materials and combinations of materials were used for various types of modelling works. A good classification or model materials was given by Stimpson (1970) based on differences in the components and applications for different purposes. Some of the materials used include Portland cement Mortar, plaste, concrete, pumice, cork, etc. The materials used most frequently are either plaster or cement with various filler materials (Hobbs, 1966; Saucier, 1967; Rosenblad, 1968: Johnston and Choi, 1986; Indraratna, 1990; Gu and Mostyn, 1992: Gu. Jafari and Mostyn, 1993). Plaster and filler materials were the most practical and feasible for modelling brittle rocks (Saucier, 1967). The development of an adequate rock-like material had been a difficult task. The investigations done in this area are valuable but all works represent soft rock with a low unconfined compressive strength (< 8 MPa) and the model materials behave in a brittle manner under low confining pressures only. Rock generally is known as a brittle material and most rocks have a high strength and they behave in a brittle manner even under high values of confining pressure. Further investigations are needed to find a rock-like material with a wide range or porosity, density and a medium range or strength that behaves in a brittle manner similar to rock under a high can lining pressure in triaxial tests. The constituents of plaster (patternstone U), crushed sand, water and borax were selected among different materials to make the model material. The constituent materials greatly affect the technique of modelling and the mechanical properties of the specimens. Crushed sands having different grain sizes from the same rock were tested to find a critical range of grain sizes. Different ratios, by weights, of plaster, crushed sand, water and borax were tried to find critical constituents to model the specimens successfully. Two methods, compacting the mixture of model material.

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