scholarly journals Thermal Liability of Hyaloclastite in the Krafla Geothermal Reservoir, Iceland: The Impact of Phyllosilicates on Permeability and Rock Strength

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-20 ◽  
Author(s):  
Josh Weaver ◽  
Guðjón H. Eggertsson ◽  
James E. P. Utley ◽  
Paul A. Wallace ◽  
Anthony Lamur ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Thermal Treatment ◽  
Elevated Temperatures ◽  
Gas Permeability ◽  
Temperature Fluctuations ◽  
Confining Pressure ◽  
Bulk Rock ◽  
Geothermal Fields ◽  
Triaxial Compressive Strength ◽  
The Impact

Geothermal fields are prone to temperature fluctuations from natural hydrothermal activity, anthropogenic drilling practices, and magmatic intrusions. These fluctuations may elicit a response from the rocks in terms of their mineralogical, physical (i.e., porosity and permeability), and mechanical properties. Hyaloclastites are a highly variable volcaniclastic rock predominantly formed of glass clasts that are produced during nonexplosive quench-induced fragmentation, in both subaqueous and subglacial eruptive environments. They are common in high-latitude geothermal fields as both weak, highly permeable reservoir rocks and compacted impermeable cap rocks. Basaltic glass is altered through interactions with external water into a clay-dominated matrix, termed palagonite, which acts to cement the bulk rock. The abundant, hydrous phyllosilicate minerals within the palagonite can dehydrate at elevated temperatures, potentially resulting in thermal liability of the bulk rock. Using surficial samples collected from Krafla, northeast Iceland, and a range of petrographic, mineralogical, and mechanical analyses, we find that smectite dehydration occurs at temperatures commonly experienced within geothermal fields. Dehydration events at 130, 185, and 600°C result in progressive mass loss and contraction. This evolution results in a positive correlation between treatment temperature, porosity gain, and permeability increase. Gas permeability measured at 1 MPa confining pressure shows a 3-fold increase following thermal treatment at 600°C. Furthermore, strength measurements show that brittle failure is dependent on porosity and therefore the degree of thermal treatment. Following thermal treatment at 600°C, the indirect tensile strength, uniaxial compressive strength, and triaxial compressive strength (at 5 MPa confining pressure) decrease by up to 68% (1.1 MPa), 63% (7.3 MPa), and 25% (7.9 MPa), respectively. These results are compared with hyaloclastite taken from several depths within the Krafla reservoir, through which the palagonite transitions from smectite- to chlorite-dominated. We discuss how temperature-induced changes to the geomechanical properties of hyaloclastite may impact fluid flow in hydrothermal reservoirs and consider the potential implications for hyaloclastite-hosted intrusions. Ultimately, we show that phyllosilicate-bearing rocks are susceptible to temperature fluctuations in geothermal fields.

scholarly journals Fire Resistance Behaviour of Geopolymer Concrete:An Overview

Buildings ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 82
Author(s):  
Salmabanu Luhar ◽  
Demetris Nicolaides ◽  
Ismail Luhar
Keyword(s):  
Compressive Strength ◽  
Thermal Resistance ◽  
Building Materials ◽  
Elevated Temperatures ◽  
Construction Materials ◽  
Flexural Behavior ◽  
Thermal Shrinkage ◽  
Physico Chemical ◽  
The Impact ◽  
Loss Of Strength

Even though, an innovative inorganic family of geopolymer concretes are eye-catching potential building materials, it is quite essential to comprehend the fire and thermal resistance of these structural materials at a very high temperature and also when experiencing fire with a view to make certain not only the safety and security of lives and properties but also to establish them as more sustainable edifice materials for future. The experimental and field observations of degree of cracking, spalling and loss of strength within the geopolymer concretes subsequent to exposure at elevated temperature and incidences of occurrences of disastrous fires extend an indication of their resistance against such severely catastrophic conditions. The impact of heat and fire on mechanical attributes viz., mechanical-compressive strength, flexural behavior, elastic modulus; durability—thermal shrinkage; chemical stability; the impact of thermal creep on compressive strength; and microstructure properties—XRD, FTIR, NMR, SEM as well as physico-chemical modifications of geopolymer composites subsequent to their exposures at elevated temperatures is reviewed in depth. The present scientific state-of-the-art review manuscript aimed to assess the fire and thermal resistance of geopolymer concrete along with its thermo-chemistry at a towering temperature in order to introduce this novel, most modern, user and eco-benign construction materials as potentially promising, sustainable, durable, thermal and fire-resistant building materials promoting their optimal and apposite applications for construction and infrastructure industries.

scholarly journals Study on the impact of confining pressure on gas permeability of tight sandstone cores

2021 ◽  
Vol 2076 (1) ◽  
pp. 012006
Author(s):  
Jianxiang Tong ◽  
Hengyang Wang ◽  
Yuyi Wang ◽  
Ya Zhang ◽  
Xiaohe Huang
Keyword(s):  
Power Function ◽  
Rate Coefficient ◽  
Gas Permeability ◽  
Confining Pressure ◽  
Experimental Sample ◽  
Tight Sandstone ◽  
Change Rate ◽  
Shengli Oilfield ◽  
Confining Pressures ◽  
The Impact

Abstract Taking the tight sandstone core of Shengli Oilfield as the experimental sample, this paper studies the permeability variation of the tight sandstone under different confining pressures. The experimental results show that when the pore pressure is constant, the measured gas permeability of core decreases with the increase of confining pressure. Power function is more reasonable to describe the influence of confining pressure on permeability of tight sandstone between power function and exponential function. Analyze the impact of confining pressure on gas permeability of tight sandstone cores by using permeability change rate coefficient D and coefficient S.

scholarly journals Experimental Study on Triaxial Unloading Failure of Deep Composite Coal-Rock

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Xin Li ◽  
Hao Li ◽  
Zhen Yang ◽  
Zhongxue Sun ◽  
Jiayu Zhuang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Failure Criterion ◽  
Confining Pressure ◽  
Exponential Relationship ◽  
Partial Fracture ◽  
Triaxial Compressive Strength ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Coal Rock ◽  
And Control

With the deep mining of coal, the phenomenon of high ground stress is more likely to cause dynamic disaster. In view of the above problems, this paper takes the unloading process of coal mining as the background to study the effects of mining rates under different conditions on the mechanical properties and triaxial failure criterion of composite coal-rock, so as to provide a theoretical basis for the prevention and control of dynamic disasters in coal mines. The composite coal-rock models with a composite ratio of 1 : 1 : 1 were tested under different unloading rates or confining pressures. The results show that the triaxial unloading process of coal-rock can be divided into five stages: compaction, single elasticity, elastic-plastic unloading, partial fracture, and complete fracture. In this paper, the failure criterion of composite coal-rock triaxial unloading is derived. The unloading rate has an exponential relationship with the triaxial compressive strength, and the relationship between initial confining pressure and compressive strength is linear. The triaxial compressive strength is determined by both. The peak strains ε of all samples under different unloading conditions were around 0.01. And initial confining pressure had an influence on the strain variation trend during the unloading of composite coal-rock. The higher the initial confining pressure, the greater the elastic modulus. In addition, an increase of initial confining pressure led to the increase of the total energy converted into dissipated part in the process of fracture and caused the obvious increase of the rebound characteristics of the curve. However, the unloading rate had no influence on the strain trend.

The mechanical behavior of Anvil Points oil shale at elevated temperatures and confining pressures

1983 ◽  
Vol 20 (2) ◽  
pp. 344-352 ◽  
Author(s):  
David H. Zeuch
Keyword(s):  
Compressive Strength ◽  
Oil Shale ◽  
Elevated Temperatures ◽  
Constant Strain Rate ◽  
Confining Pressure ◽  
Compression Tests ◽  
Confining Pressures ◽  
Strain Rate Compression ◽  
Effects Of Temperature ◽  
Good Agreement

Twenty-one constant-strain-rate compression tests have been performed on 80 mL/kg (20 gallons/ton) Anvil Points oil shale at elevated temperatures (50–200 °C) and confining pressures (0.5–40 MPa). The strength of oil shale increases approximately linearly with confining pressure and decreases nonlinearly with temperature. Ductility is greatly enhanced by the application of confining pressure. Elevated temperatures have little influence on ductility at low confining pressures; however, temperature exerts a progressively more pronounced influence on ductility with increasing confining pressure. A purely empirical failure law, incorporating the effects of temperature and confining pressure, has been fitted to the data. The failure law is in good agreement with the results of other studies on the compressive strength of oil shale. Keywords: oil shale, strength–temperature–pressure behaviour, rock mechanics, kerogen.

Triaxial Testing of Freshwater Ice at Low Confining Pressures

1991 ◽  
Vol 113 (3) ◽  
pp. 260-265 ◽  
Author(s):  
J. P. Nadreau ◽  
A. M. Nawwar ◽  
Y. S. Wang
Keyword(s):  
Compressive Strength ◽  
Strain Rate ◽  
Confining Pressure ◽  
Peak Temperature ◽  
Triaxial Testing ◽  
Brittle Transition ◽  
Freshwater Ice ◽  
Triaxial Compressive Strength ◽  
Confining Pressures ◽  
Ductile To Brittle Transition

Tests have been conducted on freshwater columnar ice samples to determine the uniaxial and triaxial compressive strength of the ice. Four parameters were varied. The confining pressure was increased up to 2.85 MPa (400 psi) in steps of 0.7 MPa (100 psi). The strain rate was varied in order to obtain the ductile to brittle transition peak. Temperature was kept mainly at −2°, with two series at −10°C and −20°C, and samples were machined with axes parallel, perpendicular or at a 45-deg angle to the direction of ice growth. The results are presented within their original context, but analyzed with reference to recent studies conducted on the multiaxial behavior of ice.

scholarly journals Impact Compression Test and Numerical Simulation Analysis of Concrete after Thermal Treatment in Complex Stress State

Materials ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 1938 ◽  
Author(s):  
Yue Zhai ◽  
Yubai Li ◽  
Yan Li ◽  
Yunsheng Zhang ◽  
Fandong Meng ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Thermal Treatment ◽  
Compression Test ◽  
Loading Rate ◽  
Confining Pressure ◽  
Material Strength ◽  
Radial Deformation ◽  
Impact Compression ◽  
Uniaxial Test ◽  
The Impact

To study the dynamic mechanical properties and fracture law of concrete after thermal treatment and reveal its mechanism, the impact compression test was carried out on different thermal-treated (400–800 °C) concrete specimens using a split Hopkinson pressure bas (SHPB) system. By using ANSYS/LS-DYNA, the finite element numerical simulation of the test process was illustrated. The research showed that under passive confining pressure, the more the loading rate is increased, the more obvious the effect of the passive confining pressure on the concrete specimen, as well as the more significant the improvement of the peak stress compared with the uniaxial test. On the other hand, as the temperature damage effect is enhanced, the increase in the material strength at different loading rates is reduced. Numerical simulations showed that in a uniaxial test, as the impact rate increases, the crack initiation time advances, and the degree of fracture increases at the same rate as that of the loading time. In the case of confining pressure, the stress gradually decreases to the edge from the center, and has a significant circumferential diffusion characteristic. The circumferential restraint of the passive confining pressure limits the radial deformation ability of the material to a certain extent, thereby increasing the axial compressive strength. In the analysis of the crushing process of concrete specimens, it was found that the fracture form showed a strong rate dependence. When the loading rate is low, the fracture form is a cleavage-like failure. As the loading rate increases, the fracture form changes to crush failure. The research results provide the necessary theoretical basis for the safety assessment, reinforcement, and maintenance of concrete structures after fire.

scholarly journals Experimental Study and Application of a Novel Foamed Concrete to Yield Airtight Walls in Coal Mines

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Hu Wen ◽  
Shixing Fan ◽  
Duo Zhang ◽  
Weifeng Wang ◽  
Jun Guo ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Strain Rate ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Mechanical Tests ◽  
Air Leakage ◽  
Rate Dependent ◽  
Foamed Concrete ◽  
Residual Coal ◽  
The Impact

Airtight walls are vital to prevent spontaneous combustion of residual coal as caused by air leakage. A new type of foamed concrete (FC) was developed to control air leakage. FC specimens of four densities (250, 450, 650, and 850 kg/m3) were prepared for use in a series of physical and mechanical tests. A thickener was used to control the FC shrinkage and collapse. The permeability of the FC decreased approximately exponentially with an increasing density. On the contrary, the compressive strength (σ) and elastic modulus (E) increased in exponential and linear relationship separately with the increase in density, under uniaxial compression conditions. Under triaxial compression, the compressive strength of the FC increased with an increase in confining pressure and appeared slight plastic. The impact experiment showed that the dynamic compressive strength of the FC appeared to be strain-rate dependent, and it increased with an increase in the strain rate and pressure under a confining pressure. Without a confining pressure, the variation in compressive strength exhibited a slow decrease. Applied FC resulted in a 5 MPa 28-day compressive strength of the airtight wall with no remaining fissures and with air leakage suppression to the gob.

scholarly journals Experimental Investigation on Permeability Evolution of Dolomite Caprock under Triaxial Compression

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6535
Author(s):  
Deng Xu ◽  
Jianfeng Liu ◽  
Zhide Wu ◽  
Lu Wang ◽  
Hejuan Liu ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Test Machine ◽  
Permeability Evolution ◽  
Triaxial Compressive Strength ◽  
Confining Pressures ◽  
Porosity And Permeability ◽  
The Difference ◽  
Maximum Permeability

In order to study the influence of different confining pressures on the stability and airtightness of dolomite underground gas storage, a permeability test under hydrostatic confining pressure, conventional triaxial compression test and gas–solid coupling test under triaxial compression were carried out on MTS815 test machine. During the tests, an acoustic emission (AE) monitoring system was also employed to estimate the rock damage. The experimental results showed that the relationships between permeability, porosity and hydrostatic confining pressure were exponential function and power function, respectively. Increasing confining pressure reduced the porosity and permeability of dolomite, and increased its triaxial compressive strength, but the addition of nitrogen reduced the compressive strength of dolomite by 10~30%, the higher the confining pressure, the smaller the difference. Compared with the maximum permeability under 15 MPa, confining pressure in the gas–solid coupling experiment, the maximum permeability under confining pressure of 30, 45, and 60 MPa is reduced by 42.0%, 84.4%, and 97.9%, respectively. In addition, the AE activity of dolomite decreases significantly with the increase in confining pressure, which also delayed the arrival of the AE active period.

scholarly journals Comparative Analyses Concerning Triaxial Compressive Yield Criteria of Coal with the Presence of Pore Water

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Rulin Liu ◽  
Yanbin Yu ◽  
Weimin Cheng ◽  
Qingfeng Xu ◽  
Haotian Yang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Pore Water ◽  
Yield Criterion ◽  
Triaxial Compression ◽  
Strength Criterion ◽  
Confining Pressure ◽  
Quadratic Polynomial ◽  
Yield Criteria ◽  
Triaxial Compressive Strength

The least absolute deviation is used as a metric to analyze the applicability of five yield criteria, to describe the yield characteristics of coal based on triaxial compressive strength tests on natural, water-saturated, and seepage coal samples with the presence of pore water. The results show that the strength of coal exhibits nonlinear characteristics with the increase of confining pressure, which the linear Coulomb criterion fails to authentically describe. Although the parabolic Mohr criterion can describe the nonlinearity feature more decently than the linear yield criterion, the fitting error is significant, and the uniaxial compressive strength of coal is overestimated. The Hoek-Brown criterion, quadratic polynomial criterion, and exponential criterion yield decent fitting quality for the coal rock. In particular, the exponential strength criterion can accurately reflect the actual uniaxial compressive strength of the rock. However, the differential principle yield stress for an infinite confining pressure calculated from the exponential strength criterion is lower than the measured value. Furthermore, by employing effective stress principle to analyze the yield criteria for the saturated and seepage coal samples, one can find that the quadratic polynomial criterion and the exponential criterion can also reflect the changes of yield characteristics during the fluid-solid coupling triaxial compression test.

scholarly journals The impact of changes in pore structure on the compressive strength of sulphoaluminate cement concrete at high temperature

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
J.J.K. Tchekwagep ◽  
P. Zhao ◽  
S. Wang ◽  
S. Huang ◽  
X. Cheng
Keyword(s):  
Compressive Strength ◽  
Pore Structure ◽  
Elevated Temperatures ◽  
Nitrogen Adsorption ◽  
Cement Concrete ◽  
Constant Weight ◽  
Sulphoaluminate Cement ◽  
Structure Changes ◽  
The Impact ◽  
The Relationship

Abstract The internal pore structure of sulphoaluminate cement concrete (SACC) significantly affects its mechanical properties. The main purpose of this study was to establish the relationship between pore structure changes and compressive strength after exposure to elevated temperatures. SACC samples that had been cured for 12 months were dried to a constant weight and then exposed to different temperatures (100 °C, 200 °C and 300 °C), after which the compressive strength and pore structure were measured. The pore structure of SACC was quantitatively described by mercury intrusion porosimetry (MIP) and nitrogen adsorption results. The results showed that with increased temperature, the porosity of the SACC samples also increased and the pore structure was gradually destroyed. Moreover, the SACC’s compressive strength gradually decreased with increasing temperature. The relationship between compressive strength and porosity was in close agreement with the compressive strength–porosity equation proposed by Schiller. Therefore, after extensive exposure to elevated temperature, the changes in SACC’s compressive strength can be quantitatively described by the Schiller equation.

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