Abstract
The effective stress principle (ESP) plays a basic role in geology and engineering problems as it is involved in fundamental issues concerning strain and failure of rock and soil, as well as of other porous materials such as concrete, metal powders, biological tissues, etc. Although since its introduction in the 1920s the main ESP aspects have been unravelled and theoretically derived, these do not appear to have been always entirely perceived by many in the science community dealing with ESP-related topics but having little familiarity with the complex theories of porous media and poroelasticity. The purpose of this review is to provide a guidance for the reader who needs an updated overview of the different theoretical and experimental approaches to the ESP and related topics over the past century, with particular reference to geological fracturing processes. We begin by illustrating, after some introductive historical remarks, the basic theory underlying the ESP, based on theory of elasticity methods. Then the different ESP-related theories and experimental results, as well as main interpretations of rock jointing and fracturing phenomena, are discussed. Two main classical works are then revisited, and a rigorous ESP proof is derived. Such a proof is aimed at geologists, engineers and geophysicists to become more familiar with theories of porous media and poroelasticity, being based on the classical theory of elasticity. The final part of this review illustrates some still open issues about faulting and hydraulic fracturing in rocks.
Highlights
The effective stress principle (ESP), introduced by Terzaghi during the 1920s [1,2], is involved in fundamental issues concerning strain and failure of rock and soil, as well as of other porous materials such as concrete, metal powders, biological tissues, etc., as it allows one to predict the mechanical behaviour of saturated porous media
The entire theoretical infrastructure has experienced a large development giving rise to the formation of practically autonomous scientific branches such as Theory of Porous Media, thanks to the extensive theoretical work carried out by Ehlers, De Boer, Coussy and their coauthors, [23,24,25,26,27,28,29,30] and Poroelasticity [31,32,33,34,35,36,37,38]. These theories represent an essential tool in the study of porous media in science and engineering and have unravelled and clarified several aspects of the ESP, these are so specialised that they may be accessible by few people in the scientific community, whereas many engineers, geologists and geophysicists, who often deal with themes involving the ESP, may not be familiar with them and might misinterpret some of their results
As fluid pressure acting on the fault plane walls, equal to (p0 + ∆p), is not counterbalanced by the pore pressure acting in the surrounding rock, equal to p0, the tangential stress offered at the fault plane is reduced to a greater extent than that which would be considered in terms of ordinary effective stress
Summary
The effective stress principle (ESP), introduced by Terzaghi during the 1920s [1,2], is involved in fundamental issues concerning strain and failure of rock and soil, as well as of other porous materials such as concrete, metal powders, biological tissues, etc., as it allows one to predict the mechanical behaviour of saturated porous media. The entire theoretical infrastructure has experienced a large development giving rise to the formation of practically autonomous scientific branches such as Theory of Porous Media, thanks to the extensive theoretical work carried out by Ehlers, De Boer, Coussy and their coauthors, [23,24,25,26,27,28,29,30] and Poroelasticity [31,32,33,34,35,36,37,38] These theories represent an essential tool in the study of porous media in science and engineering and have unravelled and clarified several aspects of the ESP, these are so specialised that they may be accessible by few people in the scientific community, whereas many engineers, geologists and geophysicists, who often deal with themes involving the ESP (e.g., role of pore pressure in earthquakes, jointing and hydraulic fracturing of rocks, etc.), may not be familiar with them and might misinterpret some of their results. Main aim of this review is to provide an overview of different proposed formulations for ESP as well as unravelling the underlying theory on the basis of the classical Theory of Elasticity, in order to clarify to the reader its fundamental role in geological processes and geotechnical engineering applications
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