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Abstract Limestone in volcanic basements has been identified as a hazard in terms of edifice stability due to the propensity of calcite to decompose into lime and CO2 at high temperatures (>600 °C), causing a decrease in mechanical strength. To date, such hypotheses have been tested by experiments performed at ambient pressure. The present work det...
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... used Comiso Limestone (hereafter CL), part of the large succession of thick Mesozoic to Mid-Pleistocene carbonates of the foreland area (Hyblean Plateau, Fig. 1). Cross sections suggest that the CL can be found at 4-6 km below Mt. Etna's peak (Branca et al., 2011), although rock types similar to CL may occur at shallower levels whereas large carbonate lenses are also known in the subsurface units (Wiesmaier et al., 2015). The CL formation outcrops 50 km to the south of Mt. Etna and is quarried ...
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... rock types similar to CL may occur at shallower levels whereas large carbonate lenses are also known in the subsurface units (Wiesmaier et al., 2015). The CL formation outcrops 50 km to the south of Mt. Etna and is quarried for building purposes. Sample blocks were obtained from a quarry near the town of Comiso (36 • 56 58.3 N, 14 • 36 53.6 E; Fig. 1). The formation consists mainly of mudand wackstones with occasional beds of dolomite and marls. The mineralogical composition has been characterized by XRD (see methods and results). Spectra indicate the samples consist purely of calcite (see Fig. 5). Pre-test sample characterization using a texture goniometer (Seifert-Scintag ...
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Citations
... Moreover, porosity increase might be likely related to the combination of grain crushing and crack damage [14]. The decalcination and decarbonation process can be self-limited upon decreasing oxygen fugacity [40] and increasing confinement on the rock [41,42]. ...
Assessing the rock physical and mechanical behavior under different temperatures has become of utmost importance. It is well known that thermal stresses induce significant crack damage in rocks due to thermal expansion or phase transformation and volume changes. Quantifying and forecasting the evolution of rock physical and mechanical parameters with temperature is thus crucial for evaluating rock integrity in many applications such as geothermal fields, nuclear waste storage, wildfire or volcanic processes. In marbles the degree of previous exposure to temperature and the chemical composition (i.e. calcite vs dolomite) plays a key role for controlling the mechanical evolution under temperature. Moreover separating out the energy contribution provided by anelastic processes driving crack damage and elastic reversible deformation under increasing temperature remains an open challenge. With these aims, three sample sets of marbles with different contents of calcite and dolomite from two Brazilian quarries were tested under different temperature conditions (from room temperature up to 600 °C). A marked increase of thermal cracking was observed after 400 °C, accompanying mass loss up to 1% and porosity increase. Moreover, a significant drop in seismic wave velocities, uniaxial compressive strength and electrical resistivity, in wet conditions, was also detected. Spectral behavior from seismic traces and energy dissipation from stress-strain curves were analyzed. A dominance of the dissipated energy compared to the elastic one was observed and related to the generation of new fracturing surfaces. This hypothesis was supported by the spectral behavior showing multiple scattering effects in the high frequency components, with an increase in attenuation. The results suggested that the percentage of dolomite has a high influence on the mechanical behavior even at low temperature, mirroring the prevalence of brittle processes in dolomitic marbles. This study represents a comprehensive benchmark for the study of effect of temperature on rocks because of its multidisciplinary and multimethod approach and the demonstrated sensitivity to subtle textural changes. Moreover, it provides a reliable tool for crack damage analysis at each thermal stress.
... Meng et al. [7] also showed that the rate of decrease in the strength of limestone from Xuzhuo as a function of increasing temperature did not appreciably change under confining pressures up to 30 MPa. Castagna et al. [18] found that temperature did not appreciably influence the compressive strength of Comiso limestone (Italy; porosity of 0.09) at a confining pressure of 15 MPa at temperatures up to 450 • C, but that compressive strength was reduced from~160 to~130 MPa as the temperature was increased to 600 • C. At a confining pressure of 50 MPa, Comiso limestone transitioned from brittle to ductile behaviour at temperatures ≥ 400 • C [19]. The tensile strength of limestone from Shandong Province was reduced from~7 MPa at 20 • C to~3.5 MPa at 600 • C [13]. ...
... Fire 2023, 6, 263 4 limestone (Italy; porosity of ~0.09) at a confining pressure of 15 MPa at temperatur to 450 °C, but that compressive strength was reduced from ~160 to ~130 MPa a temperature was increased to 600 °C. At a confining pressure of 50 MPa, Comiso lime transitioned from brittle to ductile behaviour at temperatures ≥ 400 °C [19]. The t strength of limestone from Shandong Province was reduced from ~7 MPa at 20 °C t MPa at 600 °C [13]. ...
Limestone is a popular building stone worldwide. In Baku in Azerbaijan, local limestones have been used in construction, including in the walled historic city centre (Old City, Icherisheher). Located in a seismically-active area, Baku is prone to post-earthquake fires that can damage buildings and monuments. Here, we test the fire resistance of local limestone by measuring its physical (connected porosity, permeability, P-wave velocity, thermal properties) and mechanical (uniaxial compressive strength, Young’s modulus) properties before and after thermal-stressing to temperatures up to 600 °C. Our results show that connected porosity and permeability increase and that P-wave velocity, thermal conductivity, thermal diffusivity, specific heat capacity, uniaxial compressive strength, and Young’s modulus decrease as a function of increasing temperature. Microstructural analyses show that these changes are the result of thermal microcracking. Samples heated to 800 °C disintegrated due to the formation of portlandite following decarbonation. The data presented herein will assist damage assessments of limestone buildings and monuments in Baku following the unfortunate event of fire.
... In volcanic contexts, inelastic compaction of edifice-forming rock (including non-volcanic basement rocks) presumably acts as a driving force in the growth and destruction life-cycle of large volcanoes (Bakker et al., 2015;Concha-Dimas et al., 2005;Heap et al., 2015c;Van Wyk De Vries & Borgia, 1996), which involves episodes of spreading that eventually leads to catastrophic collapses (Van Wyk De Vries & Francis, 1997). Since flank and/or edifice collapse models often invoke a weak/ductile internal or basal unit to explain instability and collapse (Ablay & Hürlimann, 2000;Morgan & McGovern, 2005;Voight, 2000), it is ...
Experimental rock mechanics studies underpin our understanding of the relationship between microstructural attributes and bulk mechanical properties of natural materials. Considerable progress has been made but intrinsic variability from sample to sample and structural heterogeneity remain limitations to the study of the contribution of each microstructural parameter independently. In this work, synthetic rocks for which these parameters can be predetermined and designed are used to unravel the contribution of microstructural attributes on the hydraulic and mechanical properties of rocks. Combining systematic petrophysical characterisation and experimental rock deformation methods with analyses of the microstructure, the first-order control of porosity and grain size on the onset of inelastic compaction are exposed and grain size distribution is shown to have a significant influence on the propensity for compaction localisation under triaxial loading.
... On the other hand, Shmonov et al. 17 observed an initial drop in permeability with increasing temperature, with a later increase above 300 °C. In follow-up studies, they observed a consistent decrease in permeability with increasing temperature 17 ; similarly, Bakker et al. 12 showed a permanent reduction in the permeability of limestone with increasing temperature. The observed decrease was attributed to the ductile closure of the initial pore space by dislocation creep of the minerals due to viscous relaxation induced by thermoelastic stresses, pressure solubilization, or an "excess" of thermal expansion of the rock 18 . ...
Fluid flow through crustal rocks is controlled by permeability. Underground fluid flow is crucial in many geotechnical endeavors, such as CO 2 sequestration, geothermal energy, and oil and gas recovery. Pervasive fluid flow and pore fluid pressure control the strength of a rock and affect seismicity in tectonic and geotechnical settings. Despite its relevance, the evolution of permeability with changing temperature and during deformation remains elusive. In this study, the permeability of Westerly granite at an effective pressure of 100 MPa was measured under conditions near its brittle–ductile transition, between 650 °C and 850 °C, with a strain rate on the order of 2·10 –6 s ⁻¹ . To capture the evolution of permeability with increasing axial strain, the samples were continuously deformed in a Paterson gas-medium triaxial apparatus. The microstructures of the rock were studied after testing. The experiments reveal an inversion in the permeability evolution: an initial decrease in permeability due to compaction and then an increase in permeability shortly before and immediately after failure. The increase in permeability after failure, also present at high temperatures, is attributed to the creation of interconnected fluid pathways along the induced fractures. This systematic increase demonstrates the subordinate role that temperature dilatancy plays in permeability control compared to stress and its related deformation. These new experimental results thus demonstrate that permeability enhancement under brittle–ductile conditions unveils the potential for EGS exploitation in high-temperature rocks.
... The transition between brittle and ductile deformation mode in PMMA occurs approximately in the range 80 − 110 • C [19][20][21] , which provides an essential advantage as a rock-analogue at the the brittle-ductile transition. Although experimental apparatuses can reach a temperature close to the ductile transition of certain rocks 4,22,23 and have been previously employed to study water-based supercritical hydraulic-fracturing 5 , testing at lower temperature conditions implies that the propagating fluid (water) is still in its liquid state; in combination with the low permeability of PMMA, it allows to separate the effects of pure solid rheology from the ones of low-viscosity fluid percolation. www.nature.com/scientificreports/ ...
Developing high-enthalpy geothermal systems requires a sufficiently permeable formation to extract energy through fluid circulation. Injection experiments above water’s critical point have shown that fluid flow can generate a network of highly conductive tensile cracks. However, what remains unclear is the role played by fluid and solid rheology on the formation of a dense crack network. The decrease of fluid viscosity with temperature and the thermally activated visco-plasticity in rock are expected to change the deformation mechanisms and could prevent the formation of fractures. To isolate the solid rheological effects from the fluid ones and the associated poromechanics, we devise a hydro-fracture experimental program in a non-porous material, polymethyl methacrylate (PMMA). In the brittle regime, we observe rotating cracks and complex fracture patterns if a non-uniform stress distribution is introduced in the samples. We observe an increase of ductility with temperature, hampering the propagation of hydraulic fractures close to the glass transition temperature of PMMA, which acts as a limit for brittle fracture propagation. Above the glass transition temperature, acoustic emission energy drops of several orders of magnitude. Our findings provide a helpful guidance for future studies of hydro-fracturing of supercritical geothermal systems.
... In volcanic contexts, inelastic compaction of edifice-forming rock (including nonvolcanic basement rocks) presumably acts as a driving force in the growth and destruction life-cycle of large volcanoes (Bakker et al., 2015;Concha-Dimas et al., 2005;Van Wyk De Vries & Borgia, 1996), which involves episodes of spreading that eventually leads to catastrophic collapses (Van Wyk De Vries & Francis, 1997). Since flank and/or edifice collapse models often invoke a weak/ductile internal or basal unit to explain instability and collapse (Ablay & Hürlimann, 2000;Morgan & McGovern, 2005;Voight, 2000), it is important to understand what controls the mechanical behavior of porous rocks, especially considering that porous volcanic rocks can also develop compaction bands (Heap, Kennedy, et al., 2015. ...
The fundamentals of our understanding of the mechanical compaction of porous rocks stem from experimental studies. Yet, many of these studies use natural materials for which microstructural parameters are intrinsically coupled, hampering the diagnosis of relationships between microstructure and bulk sample behavior. To probe the influence of porosity and grain size on the mechanical compaction of granular rocks, we performed experiments on synthetic samples prepared by sintering monodisperse populations of glass beads, which allowed us to independently control porosity and grain diameter. We conducted hydrostatic and triaxial compression tests on synthetic samples with grain diameters and porosities in the ranges 0.2–1.15 mm and 0.18–0.38 mm, respectively. During hydrostatic compaction, sample porosity decreased suddenly and substantially at the onset of inelastic compaction due to contemporaneous and extensive grain crushing, a consequence of the monodisperse grain size. During triaxial tests at high confining pressure, our synthetic samples failed by shear‐enhanced compaction and showed evidence for the development of compaction bands. Critical stresses at the onset of inelastic compaction map out linear‐shaped yield caps for the porosity‐grain diameter combinations for which the critical stress for inelastic hydrostatic compaction is known. Our yield caps reinforce the first‐order importance of porosity on the compactive yield strength and show, all else being equal, that grain size also exerts a first‐order control and should therefore be routinely measured. Our study further reveals the suitability of sintered glass beads as analogs for crustal rocks, which facilitate the study of the deconvolved influence of microstructural parameters on their mechanical behavior.
... These effects are much more pronounced in carbonate rocks where at temperatures between 560°C and 800°C decarbonization occurs. 2,30 Among the available laboratory tests, the physical and mechanical properties of rocks exposed to heating can be evaluated by either performing mechanical tests in controlled high-temperature conditions reproducing in-situ thermal constraints, 9,10,25,26,31 or carrying out comparative measurements before and after the thermal treatment (preand post-heating). 19 If adequate confining pressure is applied with temperature, the first methods may allow for a simulation of specific site conditions at depth (i.e. ...
... In the tested temperature range (from 105 to 600°C), the porosity rises from 0.2% to 3%, with a clear exponential increase after 200°C (porosity is still about 0.4% at this temperature) and a sharp increase after 400°C (from about 1% to 3%). This well agrees with the onset of calcite decomposition which occurs at around 560°C 30 and speeds up the micro-cracking mechanisms by phase transitions inducing rapid volume changes and extra void formations. By regression analysis, we obtain the characteristic exponential relationship from our experimental data by interpolating porosity and temperature, as follow: ...
Carbonate rocks have a widespread diffusion in the Earth crust and are extensively used in cultural heritage and buildings. These rocks can be naturally or anthropically exposed to high temperatures. Consequently, relating physical properties to temperature-induced damage is extremely important. Six sets of compositionally and texturally different carbonate rocks, spanning from limestones and marbles to dolomitic marbles, were analysed in this study. Different physical properties, such as porosity, seismic wave velocities and electrical resistivity, were measured before and after thermal treatments with heating/cooling ranges between 105 and 600°C. Microstructural observations and optical analyses were used to investigate how temperature-induced damage affects the physical
measured properties of the different microstructures. This integrated approach allowed to define a generalised relationship between physical properties and thermal-induced damage, by way of an induced damage index valid for a broad suite of carbonate rocks.
... Hajpál 2002;Mao et al. 2009;Ranjith et al. 2012;Zhang et al. 2009;Wu et al. 2013); however, the latter typically concern igneous rocks (e.g. Smith et al. 2009;Bakker et al. 2015Bakker et al. , 2016Schaefer et al. 2015;. Experimental rock properties for application within petroleum, geothermal industries and nuclear waste disposal fall into one category, typically derived from samples "tested at" a given temperature, whereas with respect to fire damage and volcanology experimental data fall in another category where samples have undergone "heat treatment" because of inherent challenges of data collections at temperatures above 300 °C. ...
Development of high-pressure, high-temperature (HPHT) petroleum reservoirs situated at depths exceeding 5 km and in situ temperature of 170 °C increases the demand for theories and supporting experimental data capable of describing temperature effects on rock stiffness. With the intention of experimentally investigating temperature effects on stiffness properties, we investigated three sandstones from the deep North Sea Basin. As the North Sea Basin is presently undergoing substantial subsidence, we assumed that studied reservoir sandstones have never experienced higher temperature than in situ. We measured ultrasonic velocities in a low- and high-stress regime, and used mass density and stress–strain curves to derive, respectively, dynamic and static elastic moduli. We found that in both regimes, the dry sandstones stiffens with increasing testing temperature and assign expansion of minerals as a controlling mechanism. In the low-stress regime with only partial microcrack closure, we propose closure of microcracks as the stiffening mechanism. In the high-stress regime, we propose that thermal expansion of constituting minerals increases stress in grain contacts when the applied stress is high enough for conversion of thermal strain to thermal stress, thus leading to higher stiffness at in situ temperature. We then applied an extension of Biot’s effective stress equation including a non-isothermal term from thermoelastic theory and explain test results by adding boundary conditions to the equations.
... Deformation of intact rock under loading controls the development of fractures and faults in the Earth's crust, which in turn influence natural phenomena such as earthquakes (Ohnaka, 2003;Pec et al., 2016;Shimamoto & Noda, 2014), volcanic eruptions (Bakker et al., 2015;Benson et al., 2008;Heap et al., 2013;Lavallée et al., 2019), and hydrothermal circulation (Lamur et al., 2017;Violay et al., 2017;. The mechanisms that control the deformation of intact rock under shearing depend on environmental variables, such as the acting temperature, stress, and strain rate (Kato et al., 2004;Kumari et al., 2017;Odedra et al., 2001;Ohnaka, 1995;Violay et al., 2012;Wong, 1982). ...
... Brittle deformation is therefore most commonly observed at low temperature and pressure and high strain rate. On the other hand of the spectrum, the ductile behavior is characterized by a lower strength, intragranular or intergranular plasticity, thermally activated viscous dissipation, strain hardening followed by perfect plasticity, and diffused deformation (Bakker et al., 2015;Karato & Wong, 1995;Reber & Pec, 2018). Some minerals such as feldspar interpose an intermediate phase of diffused microcracking and cataclastic flow to the transition between faulting and temperature-activated crystal plasticity (Tullis & Yund, 1992). ...
... Temperature increase promotes solid-state diffusion activating creep and rate-dependent permanent strain (Violay et al., 2012). Volumetric strain and porosity decrease gradually transition toward isochoric inelastic deformation at high temperature (Violay et al., 2015). Since crack growth governs a large portion of the inelastic deformation of rocks (Horii & Nemat-Nasser, 1986) until solid-state diffusion is activated, models based on damage mechanics that include permanent and rate-dependent deformation can successfully describe the processes that lead to the formation of fractures and faults (Jacquey & Cacace, 2020;Lyakhovsky et al., 1997Lyakhovsky et al., , 2011. ...
Natural phenomena such as seismicity, volcanism, and fluid circulation in volcanic areas are influenced by the mechanical response of intact basalt. When subjected to a wide range of environmental loading conditions, basalt exhibits inelastic deformation characteristics ranging from brittle to ductile behavior. In this manuscript, we present a new constitutive model of basalt that spans the brittle‐ductile transition by covering a wide range of mean effective stress, temperature, and strain rate. The model has been implemented into the automatic constitutive model code generator MFront, which we have coupled with the finite element solver OpenGeoSys. The software employed for the computations is open source, accessible and offers a versatile solution to model thermomechanical failure of rocks. Within this framework, we have performed numerical simulations that highlight the localization of strains and stresses under triaxial compression. Predictions of the constitutive response, of the depth of the brittle‐ductile transition, and of the localization patterns are in agreement with laboratory and in situ observations. The results have important geophysical implications as they provide a constitutive basis that explains the mechanisms through which basalt can deform in a brittle fashion at temperatures above 600°C.
... In a worst-case scenario this propagates to the overlying edifice, potentially causing the volcano to collapse, even during periods of eruptive quiescence (van Wyk de Vries & Francis, 1997). This may be particularly of importance for volcanoes with carbonate basements, as carbonate rocks are prone to ductile deformation behavior at relatively low temperatures, easily achieved within a volcanic system (e.g., Bakker et al., 2015;Heap et al., 2013). Known examples of such volcanoes include Merapi in Indonesia (e.g., Chadwick et al., 2007), Vesuvius (e.g., Iacono-Marziano et al., 2009), and Mt. ...
... Known examples of such volcanoes include Merapi in Indonesia (e.g., Chadwick et al., 2007), Vesuvius (e.g., Iacono-Marziano et al., 2009), and Mt. Etna in Italy (e.g., Bakker et al., 2015;Heap et al., 2013;Mollo et al., 2011). ...
... This consists of a sequence of sub-Etnean clays (known as the blue clays), resting upon an imbricated sequence of sediments of the Apennine Maghrebian Chain (AMC) such consolidated clays, marly limestones, and quartz-arenitic rocks about 2-3 km thick (Branca et al., 2011;Branca & Ferrara, 2013;Nicolosi et al., 2014;Wiesmaier et al., 2015). These in turn overlie a Mesozoic to Mid-Pleistocene carbonate succession of "Comiso" limestone and dolomite, part of the Hyblean Plateau, the undeformed foreland domain composed of a 25-to 30-km crust (Bakker et al., 2015;Heap et al., 2013;Wiesmaier et al., 2015). This formation is estimated to start 4 km underneath Mt. ...
The mechanical dynamics of volcanic systems can be better understood with detailed knowledge on strength of a volcanic edifice and subsurface. Previous work highlighting this on Mt. Etna has suggested that its carbonate basement could be a significant zone of widespread planar weakness. Here, we report new deformation experiments to better quantify such effects. We measure and compare key deformation parameters using Etna basalt, which is representative of upper edifice lava flows, and Comiso limestone, which is representative of the carbonate basement, under upper crustal conditions. These data are then used to derive empirical constitutive equations describing changes in rocks strength with pressure, temperature, and strain rate. At a constant strain rate of 10‐5 s‐1 and an applied confining pressure of 50 MPa, the brittle‐to‐ductile transitions were observed at 975 °C (Etna basalt) and 350 °C (Comiso limestone). For the basaltic edifice of Mt. Etna, the strength is described with a Mohr‐Coulomb failure criterion with μ ~ 0.704, C = 20 MPa. For the carbonate basement, strength is best described by a power law‐type flow in two regimes: a low‐T regime with stress exponent n ~ 5.4 and an activation energy Q ~ 170.6 kJ/mol and a high‐T regime with n ~ 2.4 and Q ~ 293.4 kJ/mol. We show that extrapolation of these data to Etna's basement predicts a brittle‐to‐ductile transition that corresponds well with the generally observed trends of the seismogenic zone underneath Mt. Etna. This in turn may be useful for future numerical simulations of volcano‐tectonic deformation of Mt. Etna, and other volcanoes with limestone basements.
