scholarly journals Experimental Study on Seepage and Fracture Characteristics of Cemented Rock Samples under Triaxial Stress

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 7) ◽  
Author(s):  
Chong Li ◽  
Sifeng He
Keyword(s):  
Rock Sample ◽  
Water Pressure ◽  
Probability Model ◽  
Confining Pressure ◽  
Permeability Evolution ◽  
Volume Strain ◽  
Crack Network ◽  
Rock Samples ◽  
Crack Volume ◽  
Three Stages

Abstract To study the seepage and fracture characteristics of cemented rock strata, a series of triaxial seepage tests on cemented rock samples under different confining pressures and water pressures were carried out in this study. The triaxial strength, elastic modulus, volume strain, and the permeability of the cemented rock samples were analyzed by the seepage unit connection probability model and Kozeny-Carman model. Based on test results, the stress state of cemented rock samples was divided into four stages: nonlinear compaction stage, linear elastic stage, stress yield stage, and failure and postfailure stage. The triaxial strength of the cemented rock samples gradually increased with the increase of confining pressure but decreased with the increase of water pressure. The elastic modulus of the cemented rock sample increased with the increase of confining pressure but decreased with the increase of water pressure. Besides, the volume strain of the cemented rock sample was analyzed, and the volume strain change of the cemented rock sample was also classified into three stages: the increasing stage of crack volume strain, the stable stage of crack volume strain, and the decreasing stage of crack volume strain. Based on the results of triaxial seepage tests, the evolution of permeability was divided into the declining stage, increasing stage, and redescend stage. Through the seepage unit connection probability model and Kozeny-Carman model, the evolution of crack volume was obtained, and the evolution of crack volume with axial strain was also classified into three stages: the original pore closure stage, crack network expansion stage, and crack network closure stage. The permeability evolution and the crack volume evolution were also compared. The comparison results suggest that three stages of crack volume evolution are all ahead of three stages of permeability evolution, verifying that the crack propagation induces the formation of seepage channels in cemented rock samples. This research will provide a valuable reference for the study of instability and water inrush mechanism in cemented rock strata.

scholarly journals Mechanism of Permeability Evolution for Reservoir Sandstone with Different Physical Properties

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Xianshan Liu ◽  
Ming Xu ◽  
Ke Wang
Keyword(s):  
Physical Properties ◽  
Water Pressure ◽  
Great Influence ◽  
Confining Pressure ◽  
Permeability Evolution ◽  
Mechanical Coupling ◽  
Reservoir Permeability ◽  
Reservoir Sandstones ◽  
Permeability Increase ◽  
Distinct Features

Permeability of sandstones with different properties taken from Chongqing reservoirs has been measured and deeply discussed under increasing deviatoric stress. Corresponding to the distinct features in the stress-strain behaviors, the permeability of sandstones is found to evolve with a clear permeability decrease in the initial closure region, a constant permeability value in the elastic region, a permeability increase in the crack initiation and propagation region, a sharp permeability increase in the crack growth region, and a decrease permeability in the residual stage. The results also show that the variation patterns of permeability are similar for two reservoir sandstones under combination of confining pressure and water pressure; however, the strength and permeability are smaller for the sandstone with mud than that without mud, deeply indicating that mud-like materials have a relatively great impact on the mechanical properties and permeability, so mud components cannot be ignored for prediction of reservoir permeability. Furthermore, a statistical damage constitutive model considering hydraulic-mechanical coupling process is presented to calculate the damage variable D, illustrating that larger water pressure will result in a relatively smaller damage variables D and corresponding maximum, which explains that the permeability increases more rapidly and is larger for the sandstone without mud than that with mud, and sandstone damage related to corresponding circumferential crack strain and permeability has been investigated, also implying the evolution mechanism of permeability for two sandstones with different physical properties. Therefore, it is worth pointing out that rock physical properties have a great influence on the reservoir permeability under complex extraction conditions and cannot be ignored, which is necessary to improve the recovery ratio and productivity.

scholarly journals Effect of Variable Confining Pressure on Cyclic Triaxial Behavior of K0-consolidated Soft Marine Clay

2018 ◽  
Vol 4 (4) ◽  
pp. 755
Author(s):  
Lei Sun
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Confining Pressure ◽  
Stress Path ◽  
Cyclic Stress ◽  
Marine Clay ◽  
Stress Ratios ◽  
Variable Confining Pressure

The effect of variable confining pressure (VCP) on the cyclic deformation and cyclic pore water pressure in K0-consolidated saturated soft marine clay were investigated with the help of the cyclic stress-controlled advanced dynamic triaxial test in undrained condition. The testing program encompassed three cyclic deviator stress ratios, CSR=0.189, 0.284 and 0.379 and three stress path inclinations ηampl=3,1 and 0.64. All tests with constant confining pressure (CCP) and variable confining pressure (VCP) have identical initial stress and average stress. The results were analyzed in terms of the accumulative normalized excess pore water pressure rqu recorded at the end of each stress cycle and permanent axial strain, as well as resilient modulus. Limited data suggest that these behavior are significantly affected by both of the VCP and CSR. For a given value of VCP, both of the pore water pressure rqu and permanent axial strains are consistently increase with the increasing values of CSR. However, for a given value of CSR, the extent of the influence of VCP and the trend is substantially depend on the CSR.

scholarly journals Experimental investigations of CO2 seepage behaviorin naturally fractured coal under hydro-thermal-mechanical conditions

2021 ◽  
Vol 25 (6 Part B) ◽  
pp. 4651-4658
Author(s):  
Teng Teng ◽  
Xiaoyan Zhu ◽  
Yu-Ming Wang ◽  
Chao-Yang Ren
Keyword(s):  
Gas Flow ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Experimental Investigations ◽  
Permeability Evolution ◽  
Coal Permeability ◽  
Naturally Fractured ◽  
Series Of Experiments ◽  
Fractured Coal ◽  
Increasing Temperature

Gas-flow in coal or rock is hypersensitive to the changes of temperature, confin?ing pressure and gas pressure. This paper implemented a series of experiments to observe the seepage behavior, especially the permeability evolution of CO2 in naturally fractured coal sample under coupled hydro-thermal-mechanical conditions. The experimental results show that coal permeability increases exponentially with the increasing gas pressure, and tends to be linear when the confining pressure is high. Coal permeability decreases exponentially with the increasing confining pressure. Coal permeability decreases with the increasing temperature generally, but it may bounce up when the temperature rises to high. The results provide reference for the projects of coal gas extraction and carbon dioxide geological sequestration.

scholarly journals Experimental Study on the Variation Law of Excess Pore Water Pressure at the Bottom of the Foundation Pit for Excavation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Qizhi Hu ◽  
Qiang Zou ◽  
Zhigang Ding ◽  
Zhaodong Xu
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Confining Pressure ◽  
Deep Foundation ◽  
Foundation Pit ◽  
Excess Pore Water Pressure ◽  
Accurate Expression ◽  
Excess Pore

The excavation unloading of deep foundation pits in soft soil areas often produces negative excess pore water pressure. The rebound deformation of soil on the excavation surface of the foundation pit can be predicted reliably through the accurate expression of relevant variation laws. In combination with the principle of effective stress and the general equation of unidirectional seepage consolidation, an equation for calculating the rebound deformation from the bottom in the process of foundation pit excavation unloading was obtained. Additionally, a triaxial unloading test was adopted to simulate the excavation unloading processes for actual foundation pit engineering. After studying the variation law of the excess pore water pressure generated by excavation unloading, it was found that the negative excess pore water pressure increased with increasing unloading rate, while the corresponding peak value decreased with increasing confining pressure. The equation for rebound calculation was verified through a comparison with relevant measured data from actual engineering. Therefore, it is considered that the equation can reliably describe the rebound deformation law of the base. This paper aims to guide the design and construction of deep foundation pits in soft soil areas.

scholarly journals Experimental Study on Mechanical Behavior of a New Backfilling Material: Cement-Treated Marine Clay

2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
Nan Zhou ◽  
Shenyang Ouyang ◽  
Qiangqiang Cheng ◽  
Feng Ju
Keyword(s):  
Coal Mine ◽  
Water Pressure ◽  
Confining Pressure ◽  
Secant Modulus ◽  
Marine Clay ◽  
Stress Strain ◽  
Strata Control ◽  
Strain Behavior ◽  
Versus Strain ◽  
Overlying Strata

Backfilling mining method is an overlying strata control way, which is widely used in underground coal mine. This method is effective in preventing and controlling geological disasters such as surface subsidence, mine water inrush, rock burst, and other disasters. Cement-treated marine clay (CMC) is a typical porous media, which has abundant reserves and can be used as a new backfilling material. Therefore, the mechanical characteristics of CMC are very important for overlying strata control in coal mine. To investigate stress-strain behavior of CMC, isotropic consolidated drained (CID) triaxial test and isotropic compression test (ICT) were conducted with different confining pressures in the range of 50–800 kPa. Stress-strain behavior was found similar to those of the overconsolidated stress-strain behavior as well as the pore water pressure versus strain. Stress versus strain curves under lower confining pressure 50–250 kPa presented shear dilatancy. The result shows that the peak strength increased linearly with increasing confining pressure. The internal friction angle and cohesion are 48° and 590 kPa, respectively. Before the confining pressure reaches 727 kPa, which is the primary yielding point, the secant modulus E1 (the secant modulus at 1% axial strain) and the secant modulus E50 (corresponding to the 50% of the peak point) increase initially and decrease afterwards with the increasing of confining pressure. Afterwards, the two parameters increased with increasing confining pressure. The yielding stress occurred in the stage, generating a dramatic decrease in tangent modulus. This study can be a theoretical basis for engineering application of this new backfilling material.

scholarly journals Failure and Seepage Characteristics of Gas-Bearing Coal under Accelerated Loading and Unloading Conditions

2019 ◽  
Vol 9 (23) ◽  
pp. 5141
Author(s):  
Zhang ◽  
Wang ◽  
Du ◽  
Lou ◽  
Wang
Keyword(s):  
Confining Pressure ◽  
In Situ Stress ◽  
Permeability Evolution ◽  
Permeability Model ◽  
Significant Control ◽  
Gas Dynamic ◽  
Working Face ◽  
Loading And Unloading ◽  
Seepage Characteristics ◽  
Gas Bearing

In actual mining situations, the advancing speed of the working face is usually accelerated, which may affect the failure and seepage characteristics of gas-bearing coal, and may even induce dynamic disasters. In order to discover the effects of such accelerated advancement of the working face, an experimental study on the failure and seepage characteristics of gas-bearing coal under accelerated loading and unloading conditions was carried out in this work. The results showed that the energy release was more violent and impactful under accelerated loading and unloading paths. The time required for the failure of the sample was significantly shortened. After being destroyed, the breakup of the sample was more severe, and the magnitude of the permeability was greater. Accordingly, the acceleration of the loading and unloading had significant control effects on the failure and permeability of coal and it showed a significant danger of inducing coal and gas dynamic disasters. Meanwhile, the degree of influence of the acceleration on the coal decreased with an increase in the gas pressure and increased significantly with an increase in the initial confining pressure. It was found that for a deep high-gas mine, the accelerated advancement of the working face under a high in situ stress condition would greatly increase the risk of coal and gas dynamic disasters. Then, the permeability evolution model of gas-bearing coal in consideration of changes in the loading and unloading rates was theoretically established in this work, and this permeability model was validated by experimental data. The permeability model was found to be relatively reasonable. In summary, the effects of accelerated loading and unloading on the failure and seepage characteristics of gas-bearing coal were obtained through a combination of experimental and theoretical studies, and the intrinsic relationship between the accelerated advancement of the working face and the occurrence of coal and gas dynamic disasters was discovered in this work.

scholarly journals Data processing method for experimental studies of deformation in a rock sample under uniaxial compression

2019 ◽  
Vol 129 ◽  
pp. 01018
Author(s):  
Andrei Golosov ◽  
Olga Lubimova ◽  
Mikhail Zhevora ◽  
Vladislava Markevich ◽  
Vladimir Siskov
Keyword(s):  
Rock Sample ◽  
Experimental Studies ◽  
Main Element ◽  
Theoretical Studies ◽  
Dynamic Changes ◽  
New Approach ◽  
Rock Samples ◽  
Data Processing Method ◽  
Patterns Of Behavior ◽  
Experimental And Theoretical Studies

As a result of experimental and theoretical studies, the patterns of behavior of rocks in a condition close to destructive are the focal nature of the preparation of macrocracking, which allowed us to include the mesocrack structure of the material, which is the main element in the preparation of macrocracking. Differences in this new approach to mathematical modeling will let adequately describe dissipative mesocrack structures of various hierarchical levels of geodesy, predict dynamic changes, structures and mechanical properties of both rock samples and massif, which also lead to resource-intensive experimental studies. In this paper, with usage of the methods of cluster, factor, and statistical analysis, we set the task of processing the data of experimental studies of the laws of deformation and preparing macro-fracture of rock samples by various methods, including acoustic and deformation observations.

scholarly journals Study on Damage Model and Damage Evolution Characteristics of Backfill with Prefabricated Fracture under Seepage-Stress Coupling

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jifeng Hou ◽  
Zhongping Guo ◽  
Weizhen Liu ◽  
Hengze Yang ◽  
WenWu Xie
Keyword(s):  
Mechanical Properties ◽  
Damage Evolution ◽  
Coupling Effect ◽  
Water Pressure ◽  
Damage Model ◽  
Confining Pressure ◽  
Seepage Water ◽  
Confining Pressures ◽  
Initial Fracture ◽  
Total Damage

Aiming at the backfill with prefabricated fracture under seepage-stress coupling, the concepts of fracture macrodamage, loaded mesodamage, seepage mesodamage, and total damage of backfill were proposed. Based on the macroscopic statistical damage model, the coupling effect of seepage, stress, and initial fracture was considered comprehensively and the damage model of backfill with prefabricated fracture under seepage-stress coupling was established. The mechanical properties of backfill with prefabricated fracture under different seepage water pressures and confining pressures were tested and the rationality of the model was verified. The research shows that the mechanical properties of backfill with prefabricated fracture under the seepage-stress coupling are determined by the seepage water pressure, the load, the initial fracture, and the coupling effect. Fracture and seepage have significant effects on the damage of the backfill. When the seepage water pressure is low, the fracture damage dominates; however, when the seepage water pressure is high, the seepage damage dominates; the total damage under the coupling action is more serious than the single factor. The development laws of the total damage evolution curves under different seepage water pressures and confining pressures are basically the same, and they show the S-shaped distribution law with the increase of the axial strain. With the increase of confining pressure, the damage effect of fracture and seepage on the backfill is weakened, indicating that the confining pressure has a certain inhibitory effect on the damage evolution of the backfill. The research results can provide a theoretical basis for the study of the stability of backfill with geological defects such as joints and fractures in deep high-stress and high-seepage water pressure coal mines.

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