scholarly journals Shear-induced Permeability Evolution of Sandstone Fractures

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Hongwei Zhang ◽  
Zhijun Wan ◽  
Zijun Feng ◽  
Jinwen Wu
Keyword(s):  
Shear Stress ◽  
Hydraulic Fracturing ◽  
Water Inrush ◽  
Shear Displacement ◽  
Permeability Evolution ◽  
Stick Slip ◽  
Fracture Surfaces ◽  
Flow Pathways ◽  
Induced Changes ◽  
Stable Stage

In underground coal mines, shear-induced changes in regional fluid flow are a major factor causing water inrushes from faults into working faces. Shear slip along preexisting fractures tends to be activated during hydraulic fracturing, and this movement can either enhance or diminish hydraulic fracturing efficiency. To prevent water inrush disasters and further hydraulic fracturing, understanding the evolution of shear-induced permeability in fractures in sedimentary rock is very important. In this study, the evolution of shear-induced permeability in saw-cut sandstone fractures with three different types of surface roughness was investigated by conducting triaxial shear tests and examining the 3-D topography of the unsheared and sheared fracture surfaces. The results allow several important conclusions to be drawn. (1) The permeability of fractures follows a three-stage shear-displacement-dependent evolution. The permeability remains unchanged in the first stable stage. After that, permeability decreases sharply with increasing shear displacement. Finally, the permeability enters a second stable stage. (2) The shear stress versus shear-displacement curves can also be divided into three stages, namely, a stress adjustment stage, a stage of increasing stress, and a stable stage. During the experiments, the fractures always experienced stick-slip shear in the stable stage. The oscillations of the shear stress in the stick-slip stage had a higher frequency for fractures with rougher surfaces. In addition, the rougher surfaces exhibited a greater permeability drop after shearing than that shown by smoother fracture surfaces. (3) The 3-D scanning results imply that the coupled effects of grinding (plus scraping) and sealing lead to decreased permeability. During shearing, the fracture walls grind and scrape against each other resulting in partial flattening of the fracture surface and the production of fault gouge in the fracture. This leads in turn to the flow pathways being partially sealed by crushed mineral grains.

scholarly journals Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3070
Author(s):  
Fernanda Bessa Ferreira ◽  
Paulo M. Pereira ◽  
Castorina Silva Vieira ◽  
Maria de Lurdes Lopes
Keyword(s):  
Shear Stress ◽  
Stress Relaxation ◽  
Shear Displacement ◽  
Time Dependent ◽  
Shear Behaviour ◽  
Displacement Rate ◽  
Shear Mode ◽  
Direct Shear ◽  
Constant Displacement ◽  
Shear Box

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.

Strength and permeability evolution of andesite during benchtop acid dissolution experiments: implications for volcanic systems

2021 ◽  
Author(s):  
Jamie Farquharson ◽  
Bastien Wild ◽  
Alexandra Kushnir ◽  
Michael Heap ◽  
Patrick Baud ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Physical And Mechanical Properties ◽  
Permeability Evolution ◽  
Acid Dissolution ◽  
Crater Lakes ◽  
Glass Dissolution ◽  
Order Of Magnitude ◽  
Flow Pathways ◽  
Permeability Increase ◽  
Chemical Conditions

<p>Acidic crater lakes are common features of subaerial volcanic systems; indeed, research suggests the existence of over 700 volcanic lakes around the world. Their persistence requires a regular input of water (e.g., meteoric water) at a rate that exceeds the migration of fluid from the system—for example, due to evaporation or fluid flow through the porous edifice.  Flank aquifers and fumarole fields may similarly be strongly acidic environments.</p><p>In order to explore the evolution of the physical and mechanical properties of an andesite under these field-relevant chemical conditions, we performed batch reaction experiments over timescales from 1 day to 4 months. The experiments involved immersion of a suite of samples in a solution of sulfuric acid (0.125 M; pH ∼0.6). Periodically, samples were removed and their physical and mechanical properties measured. We observe a progressive loss of sample mass, along with a general increase in porosity. We attribute this to the dissolution of plagioclase,  accompanied by the generation of a microporous diktytaxitic groundmass due to glass dissolution.</p><p>Plagioclase phenocrysts are seen to undergo progressive pseudomorphic replacement by an amorphous phase enriched in silica and depleted in other, relatively more soluble, cations (Na, Ca, and Al). In the first phase of dissolution (i.e. between 1 and 10 days), this process appears to be confined to preexisting fractures within the plagioclase phenocrysts. Ultimately, however, these phenocrysts tend toward entire replacement by amorphous silica. We do not observe evidence of induced dissolution or alteration in the other mineral constituents of the material: pyroxene, cristobalite, and titanomagnetite, specifically.</p><p>Examining the required Klinkenberg corrections during permeability measurements, we quantitatively demonstrate that the relative aperture of flow pathways increases with progressive acid immersion, by as much as a factor of five. We propose that the dissolution process results in the widening of pore throats and the improvement of pore connectivity, with the effect of increasing permeability by over an order of magnitude relative to the initial measurements. Compressive strength of our samples was also decreased, insofar as porosity tends to increase.</p><p>We highlight broader implications of the observed permeability increase and strength reduction for volcanic systems including induced flank failure and related hazards, improved efficiency of volatile migration, and attendant eruption implications.</p>

scholarly journals Experimental Investigation of Water-Inrush Risk Based on Permeability Evolution in Coal Mine and Backfill Prevention Discussion

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Meng Li ◽  
Jixiong Zhang ◽  
Weiqing Zhang ◽  
Ailing Li ◽  
Wei Yin
Keyword(s):  
Experimental Investigation ◽  
Coal Mine ◽  
Strain Softening ◽  
Water Inrush ◽  
Rock Fractures ◽  
Permeability Evolution ◽  
Testing Laboratories ◽  
Fracture Development ◽  
Confining Pressures ◽  
Maximum Permeability

Induced by coal mining, the fractures constantly occur in geologic strata until failure occurs, which provide channels for water flow. Therefore, it is essential to investigate the permeability evolution of rocks under load. Borehole sampling was conducted in a bedrock layer beneath an aquifer, and the permeability evolution of sandstone specimens under different confining pressures was tested in rock mechanics testing laboratories. The results indicated that the permeability gradually decreases with the increasing confining pressures, while the peak strength increases with the increase of confining pressures. The minimum and maximum permeabilities occurred in the sandstone specimens that were subjected to elastic deformation and strain-softening stages, respectively. The failure, and maximum permeability, of these sandstone specimens did not occur simultaneously. To prevent the flow channel being formed due to the development and failure of rock fractures, a method of backfill gob was proposed and also the influence of backfill on fracture development was discussed.

Seismic triggering of catastrophic failures on shear surfaces in saturated cohesionless soils

2005 ◽  
Vol 42 (1) ◽  
pp. 229-251 ◽  
Author(s):  
Aurelian Catalin Trandafir ◽  
Kyoji Sassa
Keyword(s):  
Shear Stress ◽  
Shear Resistance ◽  
Shear Displacement ◽  
Sliding Surface ◽  
Shear Tests ◽  
Shear Surface ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
Stress Reversals ◽  
Undrained Shear

This paper is concerned with an analysis of the seismic performance of infinite slopes in undrained conditions. The material assumed on the sliding surface is a loose saturated sand susceptible to a gradual loss in undrained shear strength after failure with the progress of unidirectional shear displacement. The undrained monotonic and cyclic shear behavior of this sand was investigated through an experimental study based on ring shear tests, with initial stresses corresponding to the static conditions on the sliding surface of the analyzed slopes. These tests provide the experimental framework for a modified sliding block method to estimate the earthquake-induced undrained shear displacements for conditions of no shear stress reversals on the sliding surface. The proposed estimation procedure incorporates the shearing resistance obtained from undrained monotonic ring shear tests to approximate the undrained yield resistance at a certain displacement during an earthquake. The term catastrophic failure is used in this study to define the accelerated motion of a potential sliding soil mass due to the static driving shear stress exceeding the reduced undrained yield resistance of the soil on the shear surface. The critical displacement necessary to trigger a catastrophic failure on the shear surface under seismic conditions was derived based on the shear resistance – shear displacement curve obtained under monotonic loading conditions. Using the shear resistance – shear displacement data from undrained monotonic ring shear tests and several processed horizontal earthquake accelerograms, the minimum peak earthquake acceleration necessary to cause a catastrophic shear failure under various seismic waveforms was estimated for conditions of no shear stress reversals on the sliding surface.Key words: earthquakes, slopes, critical shear displacement, sand, ring shear tests, undrained shear strength.

Elastoplastic constitutive model for hydraulic aperture analysis of hydro-shearing in geothermal energy development

SIMULATION ◽  
2018 ◽  
Vol 95 (9) ◽  
pp. 861-872
Author(s):  
Yong Xiao ◽  
Jianchun Guo ◽  
Hehua Wang ◽  
Lize Lu ◽  
Mengting Chen
Keyword(s):  
Shear Strength ◽  
Hydraulic Fracturing ◽  
Geothermal Energy ◽  
Energy Development ◽  
Green Energy ◽  
Shear Displacement ◽  
Natural Fracture ◽  
Roughness Coefficient ◽  
Fracture Simulation ◽  
Hydraulic Aperture

Geothermal energy is renewable, clean and green energy generated and stored in the Earth’s crust. The most important consideration for geothermal energy development in non-hydrothermal scenarios is the use of hydraulic fracturing technology to establish an effective network pathway to conduct fluid from injectors to producers. Hydraulic fracturing in geothermal wells is referred to as hydro-shearing and the aim is to improve the conductivity of natural fractures. In this paper, linear elastic constitutive relationships and shear strength of discontinuities in the pre-peak region are initially considered. Based on the dynamic frictional weakening, a proved conductive aperture and the post-peak elastoplastic constitutive models are proposed to analyze the deformation and conductivity of the natural fracture. Simulation research has shown that the joint compressive strength (JCS) mainly affects the shear displacement and hardly affects the dilation. The joint roughness coefficient (JRC) is more important for decreasing the shear strength and improves the dilation aperture. To no one’s surprise, reducing the effective normal stress is the best way for increasing the shear displacement, dilation and conductivity of the natural fracture. Almost 90% of the slip displacement and dilation occurs after fracture shear failure. This displacement not only increases the hydraulic conductivity of the fracture, but also reduces the required surface pumping pressure.

Nanoparticle localization in blood vessels: dependence on fluid shear stress, flow disturbances, and flow-induced changes in endothelial physiology

Nanoscale ◽  
2018 ◽  
Vol 10 (32) ◽  
pp. 15249-15261 ◽  
Author(s):  
M. Juliana Gomez-Garcia ◽  
Amber L. Doiron ◽  
Robyn R. M. Steele ◽  
Hagar I. Labouta ◽  
Bahareh Vafadar ◽  
...  
Keyword(s):  
Shear Stress ◽  
Fluid Shear Stress ◽  
Fluid Shear ◽  
Nanoparticle Distribution ◽  
Flow Models ◽  
Flow Disturbances ◽  
Induced Changes ◽  
Stress Flow

Hemodynamic factors drive nanoparticle distribution in vivo and in vitro in cell-based flow models.

scholarly journals Numerical Investigation of a Hydrosplitting Fracture and Weak Plane Interaction Using Discrete Element Modeling

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 535
Author(s):  
Shuaiqi Liu ◽  
Fengshan Ma ◽  
Haijun Zhao ◽  
Jie Guo ◽  
Xueliang Duan ◽  
...  
Keyword(s):  
Shear Stress ◽  
Principal Stress ◽  
Stress Ratio ◽  
Water Pressure ◽  
Maximum Shear Stress ◽  
Water Inrush ◽  
Discrete Element ◽  
Maximum Principal Stress ◽  
In Situ Stress

Water inrush caused by hydrosplitting is an extremely common disaster in the engineering of underground tunnels. In this study, the propagation of fluid-driven fractures based on an improved discrete element fluid-solid coupling method was modeled. First, the interactions between hydrosplitting fractures (HFs) and preexisting weak planes (WPs) with different angles were simulated considering water pressure in the initial fracture. Second, the influence of the in situ stress ratio and the property of WPs were analyzed, and corresponding critical pressure values of different interactions were calculated. Lastly, the maximum principal stress and maximum shear stress variation inside the pieces were reproduced. The following conclusions can be drawn: (1) Five different types of interaction modes between HFs and natural WPs were obtained, prone to crossing the WPs under inclination of 90°. (2) The initiation pressure value decreased with an increased in situ stress ratio, and the confining stress status had an effect on the internal principal stress. (3) During HFs stretching in WPs with a high elastic modulus, the value of the maximum principal stress was low and rose slowly, and the maximum shear stress value was smaller. Through comprehensive analysis, the diversity of the principal stress curves is fundamentally determined by the interaction mode between HFs and WPs, which are influenced by the variants mentioned in the paper. The analysis provides a better guideline for understanding the failure mechanism of water gushing out of deep buried tunnel construction and cracking seepage of high head tunnels.

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