The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Kyriazis Pitilakis - One of the best experts on this subject based on the ideXlab platform.
-
normalized shear modulus reduction and damping ratio curves of quartz sand and rhyolitic crushed rock
Soils and Foundations, 2013Co-Authors: K Senetakis, A Anastasiadis, Kyriazis PitilakisAbstract:Abstract This paper presents a laboratory investigation of the strain-dependent dynamic properties of volcanic granular soils composed of a rhyolitic crushed rock along with additional experiments on quartz sand through a high-amplitude resonant column testing program. The sands were tested in a dry state in torsional mode of vibration and thus the degradation of the normalized shear modulus and the increase of damping ratio in shear as a function of the shear strain amplitude ( γ ) were examined. It was revealed that, for a given mean Effective Confining Pressure ( σ m ' ) and coefficient of uniformity ( C u ), the volcanic sands showed higher linearity in comparison to the quartz sands and that this trend became more pronounced with decreasing σ m ' and increasing C u . In contrast to the general trend observed in the quartz soils, the Confining Pressure and the grain-size characteristics hardly affected the rate of normalized modulus degradation and damping increase in the volcanic sands. These differences are possibly related to the micro-mechanisms that dominate at particle contacts in the range of small to medium shear strain amplitudes. For example, the possible more pronounced crushing of the asperities during the elevation of the Confining Pressure and during the dynamic loading along with the lower inter-particle friction angle and stiffness of the volcanic sands of crushable particles in comparison to the quartz sands of stronger particles might play an important role in the energy dissipation during the dynamic excitation and thus on the rate of damping increase or modulus degradation.
-
the small strain shear modulus and damping ratio of quartz and volcanic sands
Geotechnical Testing Journal, 2012Co-Authors: K Senetakis, A Anastasiadis, Kyriazis PitilakisAbstract:The dynamic properties of soils in the region of very small strains are essential for any seismic design. This paper aims to investigate the dynamic small-strain shear modulus (GO) and damping ratio (DO) of reconstituted dry sands of variable mineralogy, shape, and grain-size distribution. In particular, the low-amplitude torsional resonant column test results of 31 specimens are synthesized, 19 specimens of natural and quarry sands predominately composed of quartz particles, and 12 specimens of volcanic sands composed of rhyolitic glassy rock of porous particles. It is concluded that the volcanic sands exhibit significantly lower GO values and slightly lower DO values in comparison to the quartz ones whilst the response of the quartz sands is significantly affected by the shape of the particles. The differences in the observed responses between quartz and volcanic sands are partially attributed to the variability in particles density, morphology, and mineralogy, as well as the higher void ratio and the lower dry density that the volcanic sands exhibit in comparison to the quartz ones. Overall, the effects of the mean Effective Confining Pressure (σm′), the void ratio (e), and the grain-size distribution on the dynamic response of the volcanic soils follow a similar trend as in the quartz sands. Using the general form of available relationships presented in the literature, and after modifying the “constant” parameters, appropriate equations, stemming from the low-amplitude resonant column data test, are proposed that may be used for the estimation of the small-strain shear modulus and damping ratio separately for natural quartz sands, quarry quartz sands, and volcanic granular soils.
Ian Main - One of the best experts on this subject based on the ideXlab platform.
-
brittle creep in basalt and its application to time dependent volcano deformation
Earth and Planetary Science Letters, 2011Co-Authors: P G Meredith, Michael J Heap, Patrick Baud, S Vinciguerra, Andrew Bell, Ian MainAbstract:Time-dependent brittle deformation is a fundamental and pervasive process operating in the Earth's upper crust. Its characterization is a pre-requisite to understanding and unraveling the complexities of crustal evolution and dynamics. The preferential chemical interaction between pore fluids and strained atomic bonds at crack tips, a mechanism known as stress corrosion, allows rock to fail under a constant stress that is well below its short-term strength over an extended period of time: a process known as brittle creep. Here we present the first experimental measurements of brittle creep in a basic igneous rock (a basalt from Mt. Etna volcano) under triaxial stress conditions. Results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress (and can be equally well fit by a power law or an exponential law): with a 20% increase in stress producing close to three orders of magnitude increase in creep strain rate. Results from stress-stepping creep experiments show that creep strain rates are also influenced by the imposed Effective Confining Pressure. We show that only part of this change can be attributed to the purely mechanical influence of an increase in Effective Pressure, with the remainder interpreted as due to a reduction in stress corrosion reactions; the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips. Overall, our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure, regardless of the level of applied stress and the time taken to reach this point. The experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law, and compared with the observed deformation history at Mt. Etna volcano. (c) 2011 Elsevier B.V. All rights reserved.
-
brittle creep in basalt and its application to time dependent volcano deformation
Earth and Planetary Science Letters, 2011Co-Authors: P G Meredith, Michael J Heap, Patrick Baud, S Vinciguerra, Andrew Bell, Ian MainAbstract:article i nfo Time-dependent brittle deformation is a fundamental and pervasive process operating in the Earth's upper crust. Its characterization is a pre-requisite to understanding and unraveling the complexities of crustal evolution and dynamics. The preferential chemical interaction between pore fluids and strained atomic bonds at crack tips, a mechanism known as stress corrosion, allows rock to fail under a constant stress that is well below its short-term strength over an extended period of time; a process known as brittle creep. Here we present the first experimental measurements of brittle creep in a basic igneous rock (a basalt from Mt. Etna volcano) under triaxial stress conditions. Results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress (and can be equally well fit by a power law or an exponential law); with a 20% increase in stress producing close to three orders of magnitude increase in creep strain rate. Results from stress-stepping creep experiments show that creep strain rates are also influenced by the imposed Effective Confining Pressure. We show that only part of this change can be attributed to the purely mechanical influence of an increase in Effective Pressure, with the remainder interpreted as due to a reduction in stress corrosion reactions; the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips. Overall, our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure, regardless of the level of applied stress and the time taken to reach this point. The experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law, and compared with the observed deformation history at Mt. Etna volcano.
-
permeability evolution during progressive development of deformation bands in porous sandstones
Journal of Geophysical Research, 2003Co-Authors: Bryne T Ngwenya, O Kwon, S C Elphick, Ian MainAbstract:[1] Triaxial deformation experiments were carried out on large (0.1 m) diameter cores of a porous sandstone in order to investigate the evolution of bulk sample permeability as a function of axial strain and Effective Confining Pressure. The log permeability of each sample evolved via three stages: (1) a linear decrease prior to sample failure associated with poroelastic compaction, (2) a transient increase associated with dynamic stress drop, and (3) a systematic quasi-static decrease associated with progressive formation of new deformation bands with increasing inelastic axial strain. A quantitative model for permeability evolution with increasing inelastic axial strain is used to analyze the permeability data in the postfailure stage. The model explicitly accounts for the observed fault zone geometry, allowing the permeability of individual deformation bands to be estimated from measured bulk parameters. In a test of the model for Clashach sandstone, the parameters vary systematically with Confining Pressure and define a simple constitutive rule for bulk permeability of the sample as a function of inelastic axial strain and Effective Confining Pressure. The parameters may thus be useful in predicting fault permeability and sealing potential as a function of burial depth and fault displacement.
Zhiming Fang - One of the best experts on this subject based on the ideXlab platform.
-
investigation of the effect of Confining Pressure on the mechanics permeability behavior of mudstone under triaxial compression
Geofluids, 2019Co-Authors: Lu Shi, Zhijiao Zeng, Zhiming FangAbstract:Injecting CO2 into a reservoir disturbs the geostress field, which leads to variations in the permeability of caprock and affects its sealing performance. In this paper, the evolution characteristics of the permeability of Yingcheng mudstone were experimentally studied during deviatoric compression under different Confining Pressures. As the Confining Pressure increased, the strength of the mudstone increased bilinearly, the angle between the fault and the maximum principle stress increased, and the fault became flatter. During compression, the permeability of mudstone first decreased and then increased and the turning point of the permeability was between the onset of dilatancy and the turning point of volumetric strain; when the fault formed, the permeability increased sharply and the fault-induced increment was reduced exponentially with increasing Confining Pressure. In addition, the mudstone transformed to the ductile failure mode when the Effective Confining Pressure was greater than 35 MPa, which means that the permeability did not jump within a small strain. Finally, a practical strain-based model of permeability evolution that separately considers compaction and dilatancy was proposed, and the predicted permeability values were in good agreement with the experimental results. This study revealed the effect of Confining Pressure on permeability evolution during compression and can help evaluate the sealing ability of mudstone caprock.
Michael J Heap - One of the best experts on this subject based on the ideXlab platform.
-
brittle creep in basalt and its application to time dependent volcano deformation
Earth and Planetary Science Letters, 2011Co-Authors: P G Meredith, Michael J Heap, Patrick Baud, S Vinciguerra, Andrew Bell, Ian MainAbstract:article i nfo Time-dependent brittle deformation is a fundamental and pervasive process operating in the Earth's upper crust. Its characterization is a pre-requisite to understanding and unraveling the complexities of crustal evolution and dynamics. The preferential chemical interaction between pore fluids and strained atomic bonds at crack tips, a mechanism known as stress corrosion, allows rock to fail under a constant stress that is well below its short-term strength over an extended period of time; a process known as brittle creep. Here we present the first experimental measurements of brittle creep in a basic igneous rock (a basalt from Mt. Etna volcano) under triaxial stress conditions. Results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress (and can be equally well fit by a power law or an exponential law); with a 20% increase in stress producing close to three orders of magnitude increase in creep strain rate. Results from stress-stepping creep experiments show that creep strain rates are also influenced by the imposed Effective Confining Pressure. We show that only part of this change can be attributed to the purely mechanical influence of an increase in Effective Pressure, with the remainder interpreted as due to a reduction in stress corrosion reactions; the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips. Overall, our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure, regardless of the level of applied stress and the time taken to reach this point. The experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law, and compared with the observed deformation history at Mt. Etna volcano.
-
brittle creep in basalt and its application to time dependent volcano deformation
Earth and Planetary Science Letters, 2011Co-Authors: P G Meredith, Michael J Heap, Patrick Baud, S Vinciguerra, Andrew Bell, Ian MainAbstract:Time-dependent brittle deformation is a fundamental and pervasive process operating in the Earth's upper crust. Its characterization is a pre-requisite to understanding and unraveling the complexities of crustal evolution and dynamics. The preferential chemical interaction between pore fluids and strained atomic bonds at crack tips, a mechanism known as stress corrosion, allows rock to fail under a constant stress that is well below its short-term strength over an extended period of time: a process known as brittle creep. Here we present the first experimental measurements of brittle creep in a basic igneous rock (a basalt from Mt. Etna volcano) under triaxial stress conditions. Results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress (and can be equally well fit by a power law or an exponential law): with a 20% increase in stress producing close to three orders of magnitude increase in creep strain rate. Results from stress-stepping creep experiments show that creep strain rates are also influenced by the imposed Effective Confining Pressure. We show that only part of this change can be attributed to the purely mechanical influence of an increase in Effective Pressure, with the remainder interpreted as due to a reduction in stress corrosion reactions; the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips. Overall, our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure, regardless of the level of applied stress and the time taken to reach this point. The experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law, and compared with the observed deformation history at Mt. Etna volcano. (c) 2011 Elsevier B.V. All rights reserved.
Jiajyun Dong - One of the best experts on this subject based on the ideXlab platform.
-
determining the maximum overburden along thrust faults using a porosity versus Effective Confining Pressure curve
Tectonophysics, 2012Co-Authors: Jiajyun DongAbstract:Abstract This study aims to quantify the tectonically induced thrusting and erosion. Here, we propose and evaluate a laboratory-based method for determining the maximum Effective stress ever sustained by a sedimentary-rock formation. The porosities of nineteen samples collected from two deep boreholes of the Taiwan Chelungpu-Fault Drilling Project were measured under different Confining stresses. The relation between measured porosity and Confining Pressure (compaction curve) is bilinear in log–log scale. The maximum Effective stress of the tested rocks was determined from the intersection point of the two straight lines of the compaction curve. The maximum Effective stresses of the rocks below the Sanyi Fault (reverse fault) are close to the in-situ vertical Effective stress. Above the Sanyi Fault (hanging wall), where the rocks have been thrust, the maximum Effective stresses of the rocks are significantly greater than the in-situ stress with an average value of 29.48 MPa. That is, the eroded thickness of the formation on the hanging wall of the Sanyi Fault is 2482 m, a value close to that determined from the geological profile (2773 m). It is inferred that the total displacements along the thrust Sanyi Fault is 11.5 km, a value close to that determined from the geological profile (14–16 km). These results indicate that the proposed laboratory-based method is potentially useful for determining the thrusting and erosion in a fold–thrust belt and the total displacements along a thrust fault.
-
stress dependence of the permeability and porosity of sandstone and shale from tcdp hole a
International Journal of Rock Mechanics and Mining Sciences, 2010Co-Authors: Jiajyun Dong, Wen Jie Wu, Toshi Shimamoto, Jih Hao Hung, Yun Hao Wu, Hiroki SoneAbstract:We utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of Pliocene to Pleistocene sedimentary rocks from a 2000 m borehole. Experiments were conducted by first gradually increasing the Confining Pressure from 3 to 120 MPa and then subsequently reducing it back to 3 MPa. The permeability of the sandstone remained within a narrow range (10 � 14 –10 � 13 m 2 ). The permeability of the shale was more sensitive to the Effective Confining Pressure (varying by two to three orders of magnitude) than the sandstone, possibly due to the existence of microcracks in the shale. Meanwhile, the sandstone and shale showed a similar sensitivity of porosity to Effective Pressure, whereby porosity was reduced by about 10–20% when the Confining Pressure was increased from 3 to 120 MPa. The experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship. To extrapolate the permeability or porosity under larger Confining Pressure (e.g. 300 MPa) using a straight line in a log–log plot might induce unreasonable error, but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range. Part of the permeability and porosity decrease observed during loading is irreversible during unloading.