Mechanical behavior of sandy facies of Opalinus Clay under different load conditions

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

“…We used a He-pycnometer (Micromeritics, AccuPyc 1340) to calculate the connected porosity of dried specimens via bulk and skeletal volume, resulting in porosities between 7.7 and 13.5vol% (average: 12.3 ± 1.2vol%). Obtained values for porosity, grain and bulk density are consistent with previous data for the sandy facies of OPA (Peters et al 2011;Yu et al 2017;Zhang and Laurich 2019). The degree of saturation was estimated from the ratio of volumetric water content and total porosity (cf., Amann et al 2011), yielding values of 94.6-97.9% (average: 96.1 ± 1.3%) after the saturation procedure.…”

“…The mineral composition of the sandy facies is dominated by clay minerals [6-70 weight percent (wt%)], quartz (16-52wt%), carbonates (7-66wt%; mainly calcite, dolomite/ankerite and siderite) and feldspars (5-15wt%). Clay minerals are mainly illite, kaolinite and chlorite (29-70wt%), as well as illite-smectite mixed layers (5-20wt%) (Thury and Bossart 1999;Pearson et al 2003;Peters et al 2011;Becker 2012;Zhang and Laurich 2019). Organic matter, rutile and apatite occur in minor amounts.…”

“…Our observation that samples taken from the sandy facies are stronger with higher elastic moduli (Figs. 4,12) is consistent with previous studies (cf., Popp and Salzer 2007;Plischke 2010, 2011;Amann et al 2011Amann et al , 2012Vöbel et al 2014;Siegesmund et al 2014;Wild and Amann 2018;Favero et al 2018;Giger et al 2018;Zhang and Laurich 2019;Minardi et al 2020).…”

“…Additionally, shales display an increased crystallographic and shape-preferred orientation of phyllosilicates, resulting in a distinct anisotropy of physical and mechanical properties related to the depositional and diagenetic conditions, mineral composition and thermal maturity (e.g., Chiarelli et al 2000;Wenk et al 2008;Sone and Zoback 2013;Siegesmund et al 2014;Liu et al 2018). Previous experimental studies show that the strength and elastic properties of clay-rich rocks depend on applied confining pressure (e.g., Ibanez and Kronenberg 1993;Niandou et al 1997;Petley 1999;Naumann et al 2007;Herrmann et al 2018), temperature (e.g., Zhang et al 2007;Masri et al 2014;Rybacki et al 2015;Liu et al 2019), strain rate (e.g., Swan et al 1989;Chong and Boresi 1990;Kwon and Kronenberg 1994;Al-Bazali et al 2008;Bonnelye et al 2017a, b;Hou et al 2019), and water content (e.g., Valès et al 2004;Zhang et al 2012;Wild et al 2015;Zhang and Laurich 2019).…”

“…For the safety assessment of OPA as a potential repository formation, prior laboratory deformation experiments have mainly focused on the characterization of the anisotropic and hydro-mechanically coupled behavior related to the excavation processes as well as on the determination of effective strength and stiffness parameters of the homogeneous, clay-rich shaly facies (e.g., Corkum and Martin 2007;Naumann et al 2007;Popp and Salzer 2007;Amann et al 2011Amann et al , 2012Wild et al 2015;Zhang et al 2017;Favero et al 2018;Giger et al 2018;Orellana et al 2018Orellana et al , 2019Wild and Amann 2018;Minardi et al 2020). However, due to its higher elastic moduli, the sandy facies has recently gained importance in research (Kaufhold et al 2013(Kaufhold et al , 2016Siegesmund et al 2014;Minardi et al 2016;Jaeggi et al 2017;Zhang and Laurich 2019). The sandy facies of OPA displays a pronounced, fabric related heterogeneity that is characterized by an alternated bedding of quartz-and clay-rich layers (Peters et al 2011;Kaufhold et al 2013;Houben et al 2014).…”