scholarly journals Experimental Study on Seepage Properties of Postpeak Fractured Rocks under Cyclic Loading-Unloading Confining Stress and Axial Stress

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xiaobo Zhang ◽  
Zuhao Xia ◽  
Chi Yao ◽  
Jianhua Yang ◽  
Mingdong Yang
Keyword(s):  
Cyclic Loading ◽  
Permeability Coefficient ◽  
Fractured Rocks ◽  
Axial Stress ◽  
Rock Fracture ◽  
Complex Loading ◽  
Seepage Flow ◽  
Confining Stress ◽  
Fractured Sandstone ◽  
Seepage Properties

Excavation in rock masses always encounters safety problems from rock fracture seepage in water-rich areas, which needs to be paid much attention, especially for fractured rocks under complicated stress state. For this reason, the permeability of fractured sandstone and granite is experimentally investigated under cyclic loading-unloading confining stress and axial stress. The variation of permeability coefficient and seepage flow with increasing and decreasing the confining stress and axial stress are comprehensively analyzed. Results show that the changing patterns of permeability with loading-unloading cycles of confining stress for both fractured sandstone and granite are similar. The permeability is most sensitive to the initial loading-unloading stages. After several loading-unloading cycles, the confining stress has little effect on permeability. The seepage flow decreases as the confining stress is unloaded to the same level in the loading process, indicating a hysteresis effect on the recovery of seepage capacity. The seepage properties under cyclic loading-unloading the axial stress are quite different from those under the confining stress. The permeability of fractured sandstone is most sensitive to the first cycle of loading-unloading of axial stress. The irrecoverable shear slide between fractures under the axial stress causes dilatancy or contraction, which makes the permeability coefficient to consecutively decrease at the subsequent cycles. The permeability of granite first decreases during the first loading of axial stress, while this trend is disordered at the subsequent stages no matter loading or unloading the axial stress. This is because of the accumulation of breakage fragments between fractures, which further disturbs the seepage flow. These findings may be useful for further understanding the seepage properties of fractured granite and sandstone under complex loading-unloading history.

Study on Characteristic of Saturated Soft Clay under one-Way Cyclic Loading

2010 ◽  
Vol 168-170 ◽  
pp. 690-695
Author(s):  
Tian Jun Liu ◽  
Guan Feng An ◽  
Hong Bin Zhang
Keyword(s):  
Cyclic Loading ◽  
Axial Stress ◽  
Soft Clay ◽  
Liquid Limit ◽  
Triaxial Tests ◽  
Confining Stress ◽  
Traffic Loading ◽  
Critical Dynamic ◽  
The Pearl River ◽  
Saturated Soft Clay

Simulating traffic loading, the high liquid limit clay specimens and the low liquid limit clay specimens of the Pearl River delta are engaged in cyclic triaxial tests under one-way cyclic loading respectively. The influence of axial stress, confining stress and plasticity index are taken into account. A critical dynamic stress ratio of saturated soft clay under one-way cyclic loading and the variations of axis strain and pore pressure with number of cycles were obtained. The conclusions are helpful to compute the settlement of saturated soft foundation under traffic loading after work.

scholarly journals A Water-Rock Coupled Model for Fault Water Inrush: A Case Study in Xiaochang Coal Mine, China

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Luyuan Wu ◽  
Haibo Bai ◽  
Chao Yuan ◽  
Guangming Wu ◽  
Changyu Xu ◽  
...  
Keyword(s):  
Fracture Zone ◽  
Permeability Coefficient ◽  
Axial Stress ◽  
Water Inrush ◽  
Coupled Model ◽  
Fault Zones ◽  
Fractured Zone ◽  
Fault Fracture Zone ◽  
Fractured Sandstone

Water inrush disasters in mining frequently occur under the influence of confined water-bearing fault zones. Therefore, investigating the fault water inrush mechanism is necessary to reduce the number of occurrences of this type of disaster. In fault zones, the rock is highly fractured, and the mechanism of water conduction is complex. In this research, the seepage mechanism of fractured sandstone in fault zones is studied through experiments, and the results indicate that the permeability coefficient of fractured sandstone depends on the axial stress and particle size. The relationship between the permeability coefficient and axial stress was an exponential relationship. Then, a water-rock coupled model is proposed based on the experimental results, which considers the different water flow patterns during water inrush disasters. Finally, a numerical simulation combined with the water-rock coupled model is conducted to investigate the fault water inrush mechanism of a case study, and the results reveal that when water inrush disasters occur during mining, two types of conditions are required. One is that the connection among the fractured zone of the coal seam roof, fault fracture zone, and aquifer fails, and the other is that the connection among the fractured zone of the water inrush prevention pillar, fault fracture zone, and aquifer fails. This study contributes to an increased understanding of the mechanism of water inrush disasters and the design of water inrush prevention pillars.

scholarly journals Hydromechanical Coupling Characteristics of the Fractured Sandstone under Cyclic Loading-Unloading

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Tong Zhang ◽  
Yang Liu ◽  
Ke Yang ◽  
Ming Tang ◽  
Xiang Yu ◽  
...  
Keyword(s):  
Rock Mass ◽  
Cyclic Loading ◽  
Enhancement Effect ◽  
Single Fracture ◽  
Hydraulic Pressure ◽  
Fracture Permeability ◽  
Confining Stress ◽  
Axial Cyclic Loading ◽  
Residual Strains ◽  
Fractured Sandstone

The mechanical and hydraulic properties of rock mass play a crucial role in underground engineering. To study the effect of hydraulic pressure, confining pressure, and axial cyclic loading-unloading on variation of the deformation and permeability in fractured rock mass, the coupling triaxial experiment of sandstone was conducted. The concept of permeability recovery rate (PRR) and permeability enhancement reduction rate (PERR) was proposed to characterize the change in permeability. The results show that the permeability of fractured sandstone quadratically varies with the change of hydraulic pressure and confining stress. In detail, the permeability decreases with the decrease of hydraulic pressure and increases with the decrease of confining stress, respectively. Compared with the single-fracture permeability, the double-fracture permeability is more sensitive to the change of hydraulic pressure. Furthermore, the permeability of fractured sandstone is more dependent on the hydraulic pressure than the confining stress. With the performance of axial cyclic loading-unloading, the permeability spirals down, and both the axial and radial residual strains quadratically evolve. Following the first axial cyclic loading-unloading, an obvious deformation memory phenomenon characterized by a parallelogram shape in axial stress-strain curves was observed for the sandstone. The cumulative PRR of 85%-95% was maintained in double-fracture sandstone. On the contrary, a fluctuation of cumulative PRR characterized by “V shape” was observed for single-fracture sandstone. The enhancement effect of axial cyclic loading on the permeability was characterized by the decrease of PERR for double-fracture sandstone and increase of PERR with a greater gradient for single-fracture sandstone.

scholarly journals Coupled Effects of Stress, Moisture Content and Gas Pressure on the Permeability Evolution of Coal Samples: A Case Study of the Coking Coal Resourced from Tunlan Coalmine

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1653
Author(s):  
Guofu Li ◽  
Yi Wang ◽  
Junhui Wang ◽  
Hongwei Zhang ◽  
Wenbin Shen ◽  
...  
Keyword(s):  
Moisture Content ◽  
Coalbed Methane ◽  
Gas Permeability ◽  
Axial Stress ◽  
Gas Pressure ◽  
Pressure Curve ◽  
Permeability Evolution ◽  
Confining Stress ◽  
Qinshui Basin ◽  
Gas Seepage

Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH4-containing coal samples. Therefore, considering the coupled effects of compressing and infiltrating on the gas permeability of coal could be more accurate to reveal the CH4 gas seepage characteristics in CBM reservoirs. In this study, coal samples sourced from Tunlan coalmine were employed to conduct the triaxial loading and gas seepage tests. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (2) The permeability versus gas pressure curve of coal presents a ‘V’ shape evolution trend, in which the minimum gas permeability was obtained at a gas pressure of 1.1MPa. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. Specifically, as the moisture content increasing from 0.18% to 3.15%, the gas permeability decreased by about 70%. These results are expected to provide a foundation for the efficient exploitation of CBM in Qinshui basin.

scholarly journals Analytical Solution of Seepage Field in Karst Tunnel

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Chong Jiang ◽  
Han-song Xie ◽  
Jia-li He ◽  
Wen-yan Wu ◽  
Zhi-chao Zhang
Keyword(s):  
Analytical Solution ◽  
Permeability Coefficient ◽  
Complex Function ◽  
Great Influence ◽  
Pressure Head ◽  
Seepage Flow ◽  
Seepage Field ◽  
Karst Tunnel ◽  
Lining Structure ◽  
Initial Support

An analytical solution for the seepage field in water-filled karst tunnel is derived based on the inversion of complex function and groundwater hydraulics theory. The solution considers the distance between the tunnel and the cavern, the size of the cavern, and the properties of the lining structure, such as the permeability coefficient as well as the radius of the grouting ring. This paper also performed numerical simulations for two cases: the application of gravity and the absence of gravity. The numerical solution was obtained to verify the analytical solution, and a good agreement was found. Then, the effect of parameters is discussed in detail, including the distance between the tunnel and the cavern, the radius of the cavern, the grouting ring, and the initial support. The results show that when the radius of the cavern is constant, the pressure head and seepage flow decrease as the distance between the tunnel and the cavern increases. When the distance is constant, the pressure head and seepage flow increase with the increase of the radius of the cavern. In addition, the pressure head and the seepage flow decrease with the increase of the thickness of the grouting ring and decrease with the decrease of the permeability coefficient. As the thickness of the initial support increases, the pressure head gradually increases and the percolation decreases. Furthermore, due to the great influence of the grouting ring and initial support on the pressure head and seepage flow, the thickness and permeability coefficient of the grouting ring and initial support should be taken into account carefully during construction.

Study of Seepage Properties of Fractured Rock Mass Based on Improved K-Means Clustering Algorithm

2013 ◽  
Vol 405-408 ◽  
pp. 310-315
Author(s):  
Hai Qing Guo ◽  
Bo Wen ◽  
Xiao Feng Bai
Keyword(s):  
Rock Mass ◽  
Clustering Algorithm ◽  
Fractured Rock ◽  
Rock Fracture ◽  
Fractured Rock Mass ◽  
Dam Foundation ◽  
Fracture Geometry ◽  
Basic Task ◽  
Matlab Program ◽  
Seepage Properties

Seepage properties of fractured rock mass are of prime importance for hydraulic engineering and accurate description of rock fracture geometry parameters is an important and basic task in rock hydraulics. In this paper, an improved K-means clustering algorithm for structural plane of fractured rock mass was first brought forward and the corresponding Matlab program for discontinuity orientations partitioning was compiled and then used in the fitting analysis of dominant orientations of certain dam foundation rock mass. On this basis, combining calculation formulas of multi-group fractures, the permeability tensor and principle value was calculated for the actual dam foundation. The results provide a theoretical and computational reference for other similar projects.

Effect of Cyclic Loading on the Yield Surface

1979 ◽  
Vol 101 (1) ◽  
pp. 59-63 ◽  
Author(s):  
F. Ellyin ◽  
K. W. Neale
Keyword(s):  
Aluminum Alloy ◽  
Steady State ◽  
Cyclic Loading ◽  
Yield Surface ◽  
Stress Ratio ◽  
Axial Stress ◽  
Repeated Loading ◽  
Plastic Response ◽  
Initial Yield ◽  
Yield Surfaces

The effect of repeated loading on the yield surface is investigated experimentally for an aluminum alloy. Initial yield surfaces under combined axial stress and torsion are first obtained, and yield surfaces subsequent to steady-state plastic response are then determined for various cyclic loading programs. The results suggest that the initial yield surface expands and translates under cyclic loading and that the form of the steady-state yield surface is independent of the stress ratio.

Analysis of Elastic-Plastic Plates and Shells Under Cyclic Loading

1978 ◽  
Vol 100 (4) ◽  
pp. 344-349
Author(s):  
K. W. Neale ◽  
Z. Nazli
Keyword(s):  
Approximate Solution ◽  
Cyclic Loading ◽  
Kinematic Hardening ◽  
Axial Stress ◽  
Repeated Loading ◽  
Elastic Plastic ◽  
Plate And Shell ◽  
Rate Form ◽  
Plates And Shells ◽  
Stress States

The behavior of elastic-plastic plate and shell structures under repeated loading is considered. The typical problem is formulated in incremental or “rate” form, and a variational method is applied to furnish an approximate solution in a stepwise fashion. In the analysis, Ziegler’s model of kinematic hardening is adopted together with a generalization of Masing’s rule for multi-axial stress states in order to describe material response under cyclic loading. Examples of application of the analysis include cylindrical shells and circular plates subjected to cyclically varying loads. The accuracy of the approximate solution in each case is assessed through a comparison of numerical results with published experimental data for monotonic loading conditions.

scholarly journals Novel chemical stimulation for geothermal reservoirs by chelating agent driven selective mineral dissolution in fractured rocks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Noriaki Watanabe ◽  
Kaori Takahashi ◽  
Ryota Takahashi ◽  
Kengo Nakamura ◽  
Yusuke Kumano ◽  
...  
Keyword(s):  
Fractured Rocks ◽  
Chelating Agent ◽  
Chemical Stimulation ◽  
Mineral Dissolution ◽  
Moderate Intensity ◽  
Geothermal Systems ◽  
Confining Stress ◽  
Traditional Methods ◽  
Hydraulic Stimulation ◽  
Permeability Enhancement

AbstractImproving geothermal systems through hydraulic stimulation to create highly permeable fractured rocks can induce seismicity. Therefore, the technique must be applied at a moderate intensity; this has led to concerns of insufficient permeability enhancement. Adding chemical stimulation can mitigate these issues, but traditional methods using strong mineral acids have challenges in terms of achieving mineral dissolution over long distances and highly variable fluid chemistry. Here, we demonstrate a novel chemical stimulation method for improving the permeability of rock fractures using a chelating agent that substantially enhances the dissolution rate of specific minerals to create voids that are sustained under crustal stress without the challenges associated with the traditional methods. Applying this agent to fractured granite samples under confining stress at 200 °C in conjunction with 20 wt% aqueous solutions of sodium salts of environmentally friendly chelating agents (N-(2-hydroxyethyl)ethylenediamine-N, N′, N′-triacetic acid and N, N-bis(carboxymethyl)-l-glutamic acid) at pH 4 was assessed. A significant permeability enhancement of up to approximately sixfold was observed within 2 h, primarily due to the formation of voids based on the selective dissolution of biotite. These results demonstrate a new approach for chemical stimulation.

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