Estimation of the damage of a porous limestone from continuous (P- and S-) wave velocity measurements under uniaxial loading and different hydrous conditions

Abstract

S U M M A R YThe damage of a porous rock (Euville oolitic limestone) was studied through uniaxial stresscycling tests. An experimental device, allowing the simultaneous and continuous measurement of strains (in two perpendicular directions) and five elastic wave hree P waves and two S waves) velocities in two different directions under fully controlled hydrous conditions, was developed for the work presented in this paper. Hence, the damage was monitored in a really precise and continuous way through the evolution of dynamic and static elastic moduli. The evolutions of wave velocities and elastic moduli, which reproduce very remarkably the shape of the stress-strains curves, showed that the limestone, initially isotropic, became progressively anisotropic during uniaxial loading due to microcrack damage. Indeed, even if the creation of microcracks is probably scattered and isotropic before the coalescence of microcracks, as shown in past studies, pre-existing microcracks and penny-shaped pores which are perpendicular (or almost perpendicular) to the uniaxial stress direction closed, whereas axially-oriented microcracks opened. The anisotropy of the damage is completely reversible but some of the damage is irreversible. V P(90 • ) , which cannot record the opening of these microcracks, started to decrease just before the macroscopic failure of the sample and can detect, therefore, very precisely the macroscopic failure of the material. The influence of water on the strength and deformation of the Euville limestone was analysed by considering both the hydromechanical and physio-chemical ('Rehbinder effect', intergranular pressure solution and subcritical cracking) effects of water.

Experimental identification of the transition from elasticity to inelasticity from ultrasonic attenuation analyses

“…Elastic wave velocities are generally reduced by the presence of open microcracks and fractures and during an increase in fracture density (Peacock et al, 1994;Sayers and Kachanov, 1995;Saenger and Shapiro, 2002;Schubnel and Guéguen, 2003;Sarout et al, 2017). Similar to changes in velocities during fracturing and compaction (e.g., Fortin et al, 2006Fortin et al, , 2007Eslami et al, 2010;Nicolas et al 2016Nicolas et al , 2017Bonnelye et al, 2017), elastic moduli can also be affected by the increase in damage in a rock body (e.g., Sarout and Guéguen, 2007;Heap et al, 2010). Therefore, spatial changes in elastic wave velocity may reveal fracture-related rock properties (e.g., increase or decrease in fracture density).…”

“…With increasing stress, fractures nucleate, grow, and coalesce until a connected network of fractures has developed, at which point, macroscopic failure of the rock sample occurs (Kranz, 1983;Paterson and Wong, 2005). The formation of new fractures beyond the elastic limit generally decreases the wave velocity (Hadley, 1976;Granryd et al 1983;Yukutake, 1989;Sayers, 2002a;Fortin et al, 2007;Eslami et al, 2010;Nicolas et al 2016Nicolas et al , 2017Bonnelye et al, 2017). However, the change in attenuation during the fracturing process beyond the elastic limit has not yet been investigated extensively (Couvreur et al, 2001;Goodfellow et al, 2015); it is the main objective of this study.…”

Effects of mineral suspension and dissolution on strength and compressibility of soft carbonate rocks

“…From an engineering point of view it is noted that calcarenites (but also other rocks as chalk and loess) may lose almost instantly up to 60% of their dry uniaxial compression strength and stiffness after saturation with water (Brignoli et al, 1995;Papamichos et al, 1997;Lagioia et al, 1998;Castellanza et al, 2009;Collins and Engineering Geology 184 (2015) 1-18 Sitar, 2009;Eslami et al, 2010;. Short-term sequential wetting and drying cycles (a series of 5, 10 and 15 cycles) have been found to cause a significant reduction in the uniaxial compression strength (3.6, 25, 45%) compared to the dry material associated with a slight weight loss (0.12, 0.17 and 0.27%) in fine-grained calcarenites.…”

P-wave velocity changes in freezing hard low-porosity rocks: a laboratory-based time-average model

“…In contrast, "induced anisotropy" through pores, cracks and fractures corresponds to stress. Stress increase due to loading can preferentially close pre-existing microcracks perpendicular to stress direction and decreases anisotropy (Eslami et al, 2010;Heap et al, 2010;Wassermann et al, 2009). However, stress increase can also lead to preferential opening of axially orientated microcracks (Eslami et al, 2010) or microcrack generation due to threshold surpassing (Heap et al, 2010;Wassermann et al, 2009), which then enhances anisotropy.…”

“…P-wave velocity will increase due to decreasing porosity if the confining pressure does not surpass the damage threshold and porosity increase due to microcracking (Eslami et al, 2010;Heap et al, 2010;Wassermann et al, 2009). In measurements with high confining pressures, the effect of pores is negligible but the effects of cracks become more important (Takeuchi and Simmons, 1973).…”