Influence of thermal and mechanical cracks on permeability and elastic wave velocities in a basalt from Mt. Etna volcano subjected to elevated pressure

Fortin, Jérôme; Stanchits, Sergei; Vinciguerra, Sergio; Guéguen, Yves

doi:10.1016/j.tecto.2010.09.028

Cited by 138 publications

(131 citation statements)

References 38 publications

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“…On the other hand, the increase of vp values registered at low loads is justified by this porosity reduction (figure 4). The increase in velocity of ultrasonic waves during compression tests agrees with results published in previous works (Vinciguerra et al, 2006;Vasconcelos et al, 2008;Fortin et al, 2011, Pola et al 2012). In our case, the vp increase is larger for marbles (where the maximum increase correspond to dMb-Y marble) and lower for the micrite limestones.…”

Section: Discussionsupporting

confidence: 91%

Ultrasonic and X-ray computed tomography characterization of progressive fracture damage in low-porous carbonate rocks

Martı́nez-Martı́nez

Fusi²,

Galiana-Merino

et al. 2016

Engineering Geology

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This paper studies the fracturing process in low-porous rocks during uniaxial compressive tests considering the original defects and the new mechanical cracks in the material. For this purpose, five different kind of rocks have been chosen with carbonate mineralogy and low porosity (lower than 2%). The characterization of the fracture damage is carried out using three different techniques: ultrasounds, mercury porosimetry and X-ray computed tomography. The proposed methodology allows quantifying the evolution of the porous system as well as studying the location of new cracks in the rock samples.Intercrystalline porosity (the smallest pores with pores radius < 1 µm) shows a limited development during loading, disappearing rapidly from the porosimetry curves and it is directly related to the initial plastic behaviour in the stress-strain patterns. However, the biggest pores (corresponding to the cracks) suffer a continuous enlargement until the unstable propagation of fractures. The measured crack initiation stress varies between 0.25· p and 0.50· p for marbles and between 0.50· p and 0.85· p for micrite limestone. The unstable propagation of cracks is assumed to occur very close to the peak strength. Crack propagation through the sample is completely independent of pre-existing defects (porous bands, stylolites, fractures and veins). A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2The ultrasonic response in the time-domain is less sensitive to the fracture damage than the frequency-domain. P-wave velocity increases during loading test until the beginning of the unstable crack propagation. This increase is higher for marbles (between 15% and 30% from initial vp values) and lower for micrite limestones (between 5% and 10%). When the mechanical cracks propagate unstably, the velocity stops to increase and decreases only when rock damage is very high. Frequency analysis of the ultrasonic signals shows clear changes during the loading process. The spectrum of treated waveforms shows two main frequency peaks centred at low ( 20 kHz) and high ( 35 kHz) values. When new fractures appear and grow the amplitude of the high-frequency peak decreases, while that of the low-frequency peak increases. Besides, a slight frequency shift is observed towards higher frequencies.

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Section: Discussionsupporting

confidence: 91%

Ultrasonic and X-ray computed tomography characterization of progressive fracture damage in low-porous carbonate rocks

Martı́nez-Martı́nez

Fusi²,

Galiana-Merino

et al. 2016

Engineering Geology

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“…This compaction/dilatant evolution before failure is well known in studies dealing with granitic rocks (e.g. Tenthorey and Gerald, 2006;Zoback and Byerlee, 1975) and basaltic rocks (Fortin et al, 2011). This evolution is not observed in the experiments on metadiabase and chloritized metadiabase (Figs.…”

Section: Effects Of Deformation and Lithology On Laboratory Permeabilsupporting

confidence: 65%

Permeability of sheeted dykes beneath oceanic ridges: Strain experiments coupled with 3D numerical modeling of the Troodos Ophiolite, Cyprus

et al. 2015

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International audiencePermeability laboratory measurements under in-situ pressures, temperature and strain have been performed on three different diabase alteration facies (metadiabase, chloritized diabase, epidosite) from the Troodos Ophiolite, Cyprus. This aims to study the relations between hydrodynamics, deformation and hydrothermal reaction in the sheeted dyke complex beneath oceanic ridges. The use of water as pore fluid in these experiments favors hydrothermal fluid-rock interactions. All experiments, performed with a Paterson gas-medium apparatus, were achieved at 400 °C, 100 MPa of confining pressure and 50 MPa of pore fluid pressure, conditions at the base of sheeted dykes. Permeability was measured by injection of water and argon before, during and after coaxial deformation. Resulting textures and mineralogy were studied by microscopy and X-ray microtomography in order to identify mineral reactions and to calculate the permeability by numerical simulation after decompression.During stress loading, a compaction/dilatant evolution is observed only in experiments on epidosite. Failure tends to increase permeability by one order of magnitude. For example, using water as pore fluid, permeability measurements after macroscopic failure give the following variations from 4 × 10- 20 m2 to 2.9 × 10- 19 m2 for metadiabase, 1 × 10- 20 m2 to 2.6 × 10- 19 m2 for chloritized diabase and 6.5 × 10- 19 m2 to 3 × 10- 18 m2 for epidosite.Textures suggestive of self-healing and sealing explain permeability reduction by hydrothermal reaction after macroscopic failure. Paradoxically, even using argon as pore fluid, hydrothermal reaction is possible in metadiabases due to dehydration of chlorite. Moreover, fractures appear much finer in rocks enriched in chlorite because of formation of gouge structures. After experiments, 3D images of fracture networks enable to calculate permeability by numerical simulations which values are 4-6 orders of magnitude higher than the experimental measured values. Such results demonstrate that the geometry and the textures observed in unloaded samples are not suitable to estimate permeability and have to be very carefully interpreted

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“…Note that for glass, crack density is known from microstructural observations with an accuracy that is sufficient for calculations. For rocks, the initial crack density cannot be easily obtained from microstructural observations, but it can be inferred from ultrasonic velocities [ Fortin et al , ; Guéguen and Kachanov , ; Mallet et al , ].…”

Section: Interpretation Of the Results And Discussionmentioning

confidence: 99%

Brittle creep and subcritical crack propagation in glass submitted to triaxial conditions

et al. 2015

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An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack‐propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential‐stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during creep. The effect of temperature on creep was investigated from ambient temperature to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary creep, failure in tertiary creep was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle creep phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle creep behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.

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Influence of thermal and mechanical cracks on permeability and elastic wave velocities in a basalt from Mt. Etna volcano subjected to elevated pressure

Cited by 138 publications

References 38 publications

Ultrasonic and X-ray computed tomography characterization of progressive fracture damage in low-porous carbonate rocks

Ultrasonic and X-ray computed tomography characterization of progressive fracture damage in low-porous carbonate rocks

Permeability of sheeted dykes beneath oceanic ridges: Strain experiments coupled with 3D numerical modeling of the Troodos Ophiolite, Cyprus

Brittle creep and subcritical crack propagation in glass submitted to triaxial conditions

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