A laboratory method for determining the dissipated energy
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A laboratory method for determining the dissipated energy Á. Deli · M. Gálos · B. Vásárhelyi
Received: 15 April 2012 / Accepted: 20 July 2012 / Published online: 24 January 2013 © Akadémiai Kiadó, Budapest, Hungary 2013
Abstract It is well known, that the strength of rocks depends on the strain or stress rate. Increasing the stress or strain rate, the strength of the rock material is increasing. The goal of this paper is to present a theoretical background of this behavior. A laboratory method is suggested to determine the critical dissipated energy density (CDE) of homogeneous-isotropic rock. In case of uniaxial compression it can be calculated easily with the difference of the work done by the external force and the energy connected to the change of structure. These energies can be measured by applying different stress or strain rates, if they tend to infinite and zero. It was assumed, that the Poynting-Thomson (standard) model can be used for modeling the rheological behavior of the intact rock, and this model was applied determining the critical dissipated energy density. The uniaxial compressive tests were carried out for both “infinite” and “zero” stress rates, and the measured stress-strain curves were compared and analyzed. According to the results, the critical dissipated energy per unite volume can be used as a material constant: it is influenced by the texture of the rock, internal bonds, the cohesion, the strength of the minerals, the porosity, etc. Using seven different types of rocks the critical dissipated energy per unite volume was determined and the relationship with the compressive and tensile strength, ultrasonic wave velocity and porosity was calculated. Knowing this critical dissipated energy, probably the tunnel stability can be calculated easier, or it can be used in the calculation of the earthquakes damage, among others.
Á. Deli Hídépít˝o Soletanche-Bachy Deep foundation Ltd, Árbóc u. 6, 1133 Budapest, Hungary e-mail: [email protected] M. Gálos Dept. of Building Mat. & Engng Geol., Budapest Univ. Techn. & Economics, M˝uegyetem rkp 3, 1117 Budapest, Hungary e-mail: [email protected] B. Vásárhelyi () Dept. of Structural Engng, Pollack Mihály Faculty of Engng, Univ. of Pécs, Boszorkány u. 2, 7624 Pécs, Hungary e-mail: [email protected]
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Acta Geod Geophys (2013) 48:77–86
Keywords Poynting-Thomson model · Critical dissipated energy · Uniaxial compression 1 Introduction Zhifa et al. (2001) investigated the rheological behavior of rock in tunnel excavation. They back-analyzed a road tunnel displacement with four rheological models, namely: Kelvin body, Maxwell body, Poynting-Thomson body and Kelvin-Voigth body. When comparing these models the Poynting-Thomson (standard) model proved to be the closest to the test results. It is remarkable that the Poynting-Thomson body, more properly its generalized version, the so called inertial Poynting-Thomson body is distinguished among these models, because it can be derived by thermodynamic considerations (see Verhás 1997). That was supported als
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