Abstract
The wide range of gypsum facies observed all over the world and the strong heterogeneity that may be present even within a single facies often cause an inhomogeneous mechanical response that, if neglected, may be particularly dangerous in the framework of underground excavations. In addition, gypsum is particularly sensible to the presence of water. The high relative humidity conditions often registered in underground gypsum quarries may imply an additional worsening of mechanical properties. In the present study, the strength and the creep response of a natural gypsum rock facies are investigated, considering the influence of material heterogeneity and relative humidity conditions. The heterogeneity of the material, quantified with MIP and SEM analyses, is observed to strongly affect the mechanical response. To this intrinsic mechanical variability, the influence of an external parameter as the relative humidity is observed to generate an additional reduction of material strength and to increase the creep strain rate in the long-term tests. The effect of all these elements in the underground quarry framework is discussed and a constitutive model of these experimental results is provided.
Highlights
The increasing demand of gypsum as raw material in a wide range of industrial fields implies its extensive exploitation by both open pit and underground quarries all over the world
With the aim of providing an analysis of the most effective parameters on the mechanical response of gypsum rock in underground quarry environments, this study proposes an experimental investigation of short-term strength and creep behaviour of natural gypsum samples, considering the influence of microstructural heterogeneity, relative humidity conditions and orientation of anisotropy planes
If, during the test, the sample reaches an axial strain of 10%, the higher plate will touch the metal support and the test will continue on the two lower samples
Summary
The increasing demand of gypsum as raw material in a wide range of industrial fields (e.g. building engineering, clinical applications, agriculture, food industries and production of paints) implies its extensive exploitation by both open pit and underground quarries all over the world. Their results highlighted the achievement of accelerated creep conditions for applied stresses higher than 35% of the uniaxial shortterm strength Their experimental data were used as a reference for the formulation of a constitutive model in Nedjar and Le Roy (2013), who proposed a viscoelastic model with a damage-like mechanism active from the very first phases of the creep tests. With the aim of providing an analysis of the most effective parameters on the mechanical response of gypsum rock in underground quarry environments, this study proposes an experimental investigation of short-term strength and creep behaviour of natural gypsum samples, considering the influence of microstructural heterogeneity, relative humidity conditions and orientation of anisotropy planes. The effect of the material microstructure and anisotropy orientation on the mechanical response is experimentally tested, considering the interaction with different relative humidity conditions. The paper closes with some considerations on the scale effect, contextualising the experimental results in a real quarry framework
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