Extracting real-crack properties from non-linear elastic behaviour of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson ratios

Abstract

Abstract. Results of examination of experimental data on non-linear elasticity of rocks using experimentally determined pressure dependences of P-and S-wave velocities from various literature sources are presented. Overall, over 90 rock samples are considered. Interpretation of the data is performed using an effective-medium description in which cracks are considered as compliant defects with explicitly introduced shear and normal compliances without specifying a particular crack model with an a priori given ratio of the compliances. Comparison with the experimental data indicated abundance ( ∼ 80 %) of cracks with the normal-toshear compliance ratios that significantly exceed the values typical of conventionally used crack models (such as penny-shaped cuts or thin ellipsoidal cracks). Correspondingly, rocks with such cracks demonstrate a strongly decreased Poisson ratio including a significant (∼ 45 %) portion of rocks exhibiting negative Poisson ratios at lower pressures, for which the concentration of not yet closed cracks is maximal. The obtained results indicate the necessity for further development of crack models to account for the revealed numerous examples of cracks with strong domination of normal compliance. Discovering such a significant number of naturally auxetic rocks is in contrast to the conventional viewpoint that occurrence of a negative Poisson ratio is an exotic fact that is mostly discussed for artificial structures.

In-situ estimation of subsurface hydro-geomechanical properties using the groundwater response to Earth and atmospheric tides

“…For small strains, as relevant for this study, Zaitsev et al (2017) have shown that the occurrence of negative Poisson's ratios is not as exotic as previously thought. Considering the context of Cundall et al (2008), Gercek (2007 and Ji et al (2018), the negative Poisson's ratios derived by TSA in this paper seem plausible.…”

“…(2018) occurs both linearly and non-linearly within the negative Poisson's ratio space, depending on the confining pressure and the type of material (Zaitsev et al, 2017). Currently, no relationships between EAT and nonlinear poroelastic theory has been established within the literature.…”

“…-Currently the poroelastic response to EAT is considered to be linear. However, rocks have previously been shown to respond in a nonlinear manner for undrained, tri-axially loaded laboratory settings, particularly at small strains (Johnson and Rasolofosaon, 1996;Zaitsev et al, 2017). As in-situ derivations of rock mass (or sediment) poroelastic values without the use of assumed primary values (E, G, K, ν) is relatively novel, the implication of assuming linearity for the analysis of in-situ properties remains unknown and unverified.…”

Shallow Crustal Shear Velocity and Vp/Vs Across Southern California: Joint Inversion of Short‐Period Rayleigh Wave Ellipticity, Phase Velocity, and Teleseismic Receiver Functions

“…More generally in our model, stations outside of sedimentary basins have low Vp/Vs (<1.75) ratios (Figures 4a and 4b). While these values are lower than anticipated from previous imaging (Hauksson, 2000) and laboratory (Christensen, 1996) studies, recent work (Zaitsev et al., 2017) shows that low Vp/Vs and a negative Poisson ratio (Vp/Vs < 1.42) is not an exotic result and has been observed in a significant portion of experimental data samples (∼45%) at low confining stress (i.e., surface conditions). Previous southern California imaging studies have observed higher Vp/Vs ratios likely due to greater depth sensitivity (Hauksson, 2000; Lin & Shearer, 2007; G. Lin et al., 2007).…”

Auxeticity of Yukawa Systems with Nanolayers in the (111) Crystallographic Plane

“…Since then, one can observe quickly growing interest in this class of materials because of their unusual, counter-intuitive properties [ 25 , 26 , 27 , 28 ], which originate from various mechanisms involving both micro- and macroscopic structures [ 23 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], inter-particle interactions [ 24 , 39 , 40 , 41 ] as well as special conditions applied to the system [ 42 , 43 ]. At present, research is being conducted extensively in the pursuit for auxetic properties in already existing and new materials [ 39 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ], the fabrication of auxetic composites [ 53 , 54 , 55 ], the construction of models for explaining auxetic properties [ 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 ], and the search for new mechanisms leading to the appearance of auxetic properties in various systems. The studies on the influence of structural modifications on the auxetic properties of Yukawa crystals are an example of the latter [ 65 , 66 ].…”