Article
Engineering, Civil
Dawei Hu, Jun Li, Hui Zhou, Jingjing Lu, Dongdong Ma, Fan Zhang
Summary: The study revealed that the pressure applied through different stress paths has different impacts on the permeability of granite. The lateral deformation in confining pressure unloading tests is significantly larger than that in classical triaxial compression tests, and the permeability in confining pressure unloading tests shows a progressively increasing trend.
EUROPEAN JOURNAL OF ENVIRONMENTAL AND CIVIL ENGINEERING
(2021)
Article
Multidisciplinary Sciences
Honggang Zhao, Chao Liu, Gun Huang
Summary: The behavior of sandstone under different initial confining pressures and unloading rates was studied in triaxial experiments. It was found that sandstones exhibited shear dilatancy before failure, with crack density increasing as initial confining pressure increased. The normalized permeability was positively correlated with unloading rates, with a linear/nonlinear relationship between the permeability and volumetric strain depending on the unloading rates.
ROYAL SOCIETY OPEN SCIENCE
(2021)
Article
Geosciences, Multidisciplinary
Jinrong Cao, Linming Dou, Kunyou Zhou, Jiliang Kan, Jiazhuo Li, Yanjiang Chai
Summary: This study conducts simulations of unloading-induced coalbursts using the distinct element method. The numerical model is calibrated and validated by comparison with laboratory tests. The influence of pre-confining pressure on coalbursts is investigated, with a focus on crack propagation, fracturing process, failure pattern, and energy evolution. The results show that increasing pre-confining pressure leads to more intense coalbursts with faster completion time, and the main failure pattern transforms from tensile to shear type. Additionally, the conversion ratio of kinetic energy and frictional energy during coalbursts increases non-linearly with increasing pre-confining pressure.
FRONTIERS IN EARTH SCIENCE
(2023)
Article
Metallurgy & Metallurgical Engineering
Deng Zhang, Zai-quan Wang, Li-ming Zhang, Xiao-shan Wang
Summary: Unloading confining pressure tests were conducted on sandstone under seepage pressure to investigate the relationship between deformation characteristics, permeability, stress paths, and seepage pressure of the rock. The results showed that increasing confining pressure leads to an increase in characteristic stress and a decrease in crack strain growth rates, while increasing seepage pressure leads to a decrease in characteristic stress and an increase in crack strain growth rates.
JOURNAL OF CENTRAL SOUTH UNIVERSITY
(2023)
Article
Engineering, Geological
Long Yan, Weiya Xu, Rubin Wang, Huanling Wang, Wei-Chau Xie
Summary: This paper presents an experimental study on the mechanical behavior and permeability evolution of basalt under hydro-mechanical coupling conditions. The relationship between confining pressure and steady creep rate was described by an exponential function, while the evolution of permeability exhibited phased characteristics. These results provide insights for the long-term stability assessment of basalt under coupled hydro-mechanical conditions.
ROCK MECHANICS AND ROCK ENGINEERING
(2021)
Article
Construction & Building Technology
Jijing Wang, Hualin Zhang, Shuangxing Qi, Hanbing Bian, Xinbo Duan, Biao Long
Summary: This study investigates the micro-damage mechanism of silty mudstone through the use of nano-materials and a triaxial unloading test considering multiple paths. The results show that the initial deviatoric stress affects the peak stress, residual stress, and residual strain of the mudstone, while crack propagation on the fracture surface during unloading is influenced by both confining pressure and initial deviatoric stress. The impact of confining pressure on pore morphology diminishes as the confining pressure and initial deviatoric stress increase. In addition, the fractal dimension increases with increased confining pressure and initial deviatoric stress, leading to a transition in the pore surface from smooth to rough.
CASE STUDIES IN CONSTRUCTION MATERIALS
(2023)
Article
Mechanics
Yushun Yang, Dongming Zhang, Yun Dong, Jihua Zhang, Xiaoming Li, Chunlei Zhang, Jingke Wu
Summary: The study found that the volumetric strain gradually increases and permeability exponentially decreases with the increase in effective stress during loading axial stress. In the process of simultaneous unloading axial stress and loading confining pressure, the volumetric strain of coal sample increases while the permeability decreases exponentially with the increase in effective stress.
Article
Chemistry, Multidisciplinary
Yanwei Duan, Guohua Zhang, Tao Qin
Summary: This research simulated the failure process of rock mass caused by unloading through triaxial unloading confining pressure tests, analyzed the crack-characteristic stress, and studied the energy evolution of rock under unloading. The results showed that confining pressure greatly affected the crack closure stress and crack initiation stress. The energy characteristic parameters gradually increased with the increase in confining pressure, and the release process of releasable elastic energy after the peak stress exhibited a significant confining pressure effect.
APPLIED SCIENCES-BASEL
(2023)
Article
Chemistry, Multidisciplinary
Bin Ma, Xinchao Ding, Xingzhou Chen
Summary: The excavation-unloading damage effects of western high-geostress slopes on rock were investigated using sandstone reloading mechanical tests under pre-peak confining pressure unloading. The deformation and failure mechanisms were analyzed using the particle discrete-element method. (1) As unloading failure approached, increasing confining pressure led to a decrease in specimen bearing capacity. (2) Unloading of confining pressure promoted microdefect propagation and development, with specimens rapidly reaching the damage stress value after reaching the initiation stress value. Penetration fracture zones were more pronounced and expansive in the model, with dense crack areas concentrated in the fracture zone and surrounding area. (3) The tangential contact force exhibited the highest average interval in the direction of crack expansion and propagation. Strong force chains primarily bore external loads, while weak force chains played a key role in maintaining stability. (4) The number of cracks developing during the confining pressure unloading damage process indicated that the loading process did not cause damage to the specimens. Fracture zones further propagated and formed on dominant fractures due to the damage caused by confining pressure unloading disturbance.
APPLIED SCIENCES-BASEL
(2023)
Article
Green & Sustainable Science & Technology
Peng Zhao, Jun Liu, Derek Elsworth
Summary: This study investigates an enhanced geothermal system (EGS) reservoir with horizontal wells and multiple hydraulic fractures, focusing on the effects of complex thermal-hydraulic-mechanical interactions on the thermal unloading of rock matrix and permeability evolution. The proposed model is validated against existing analytical solutions and a demonstration project, and the impact of fracture number on heat extraction is discussed. Results show that thermal unloading-induced matrix permeability enhancement should be considered in the coupled model, as it greatly affects the maximum temperature difference and the cooling range along the production well. Generally, more fractures in the EGS lead to higher production temperatures. The fracture number plays a crucial role in considering the heat transportation rate and the cooling range in geothermal exploration, with only slight differences in heat extraction ratio between numerical cases considering both matrix and fracture geothermal exploitation.
Article
Geosciences, Multidisciplinary
Yan-Hua Huang, Sheng-Qi Yang, Shang-Yong Teng
Summary: The study found that as the effective confining pressure increased, sandstone permeability decreased nonlinearly, while as the effective confining pressure decreased, permeability increased nonlinearly. Elevated temperature decreased sandstone permeability, however, the reduction in permeability decreased with increasing temperature.
MATHEMATICAL GEOSCIENCES
(2021)
Article
Chemistry, Physical
Wei Chen, Yixuan Han, Franck Agostini, Frederic Skoczylas, Didier Corbeel
Summary: The effects of confining pressure on macro-cracked concrete samples were studied, revealing that despite mechanical closure of the crack at around 20 MPa, gas permeability continued to decrease as confinement increased. The traditional model using two parallel planes to represent permeability variations during crack closure was found to be inadequate, leading to the development of a new physical model to simulate the real behavior of the macro-crack. This new modeling approach allowed for consistent simulation of both mechanical and hydraulic behaviors under confining pressure using the same set of parameters.
Article
Environmental Sciences
Tingen Zhu, Wenping Li, Jiawei Tian, Yi Cheng, Zhenmeng Lv
Summary: The creep deformation and permeability evolution of the paleoweathered rock in the K-1/J(2) unconformity contact zone under triaxial unloading-loading confining pressure were studied. The results provide valuable information for understanding leakage from Cretaceous aquifers and regional water-level decline. The creep strain and permeability show different patterns during the confining pressure unloading and loading stages, with the average creep rate and permeability being affected by clay mineral contents and deviatoric stress.
ENVIRONMENTAL EARTH SCIENCES
(2023)
Article
Engineering, Geological
Yinda Li, Liu Han, Tao Shang
Summary: This study investigates the impact of complex triaxial unloading confined pressure conditions on the mechanical behavior and fracture mechanism of sandstone. Through various tests and initial damage states, the influence of unloading rate and initial damage on the mechanical properties of sandstone samples is analyzed. Additionally, a proposed mechanism of tensile fracture development caused by the unloading of confining pressure is discussed, along with the potential engineering disasters it may induce.
ROCK MECHANICS AND ROCK ENGINEERING
(2023)
Article
Engineering, Mechanical
Yaoyao Meng, Hongwen Jing, Xiaowei Liu, Qian Yin
Summary: This study investigates the strength, micro crack distribution, and energy evolution characteristics of stratified rock mass under unloading confining pressure conditions. Triaxial compression tests and triaxial unloading confining pressure tests were conducted at various initial unloading levels. The results indicate that the triaxial unloading confining pressure plus axial stress corresponds to a stress path between uniaxial compression and triaxial compression. As the initial unloading level increases, the specimen approaches the stress state of triaxial compression, resulting in linear increases in peak stress, peak axial strain, peak circumferential strain, and peak volume strain, and a linear decrease in Poisson's ratio. The failure type of specimens exhibits four typical characteristics. Additionally, when the bedding plane inclination is 45 degrees, 3D reconstruction and quantitative characterization of micro cracks were performed based on CT scanning results. The variations of area fraction along the specimen height displayed three typical characteristics. The stratified rock mass primarily stores and dissipates energy before the peak stress and releases and dissipates energy after the peak stress under different conditions. Furthermore, the input energy, elastic energy, dissipative energy, and energy dissipation rate at the peak stress increase approximately linearly with the increasing initial unloading level.
THEORETICAL AND APPLIED FRACTURE MECHANICS
(2023)
Article
Chemistry, Physical
Deng-Ke Wang, Shu-Min Liu, Jian-Ping Wei, Hong-Lei Wang, Bang-Hua Yao
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2017)
Article
Energy & Fuels
Yingying Li, Hongqing Cui, Ping Zhang, Dengke Wang, Jianping Wei
Article
Energy & Fuels
Xin Bai, Dongming Zhang, Sheng Zeng, Shuwen Zhang, Dengke Wang, Fulin Wang
Article
Multidisciplinary Sciences
Hongtu Zhang, Dengke Wang, Chong Yu, Jianping Wei, Shumin Liu, Jianhua Fu
Article
Geochemistry & Geophysics
Yan Wu, Dengke Wang, Xiaofei Pang, Hang Zhang
Summary: In this study, the evolution process of internal defects in coal, such as pores and fissures, was visualized using a combination of real-time computed tomography (CT) scanning test and loading test. A CT image similarity retrieval method was proposed to address the influence of axial deformation on fracture analysis. The results showed that the proposed method accurately characterized the fracture distribution and dynamic evolution law of the coal sample. Three fracture evolution stages were observed under triaxial stress: closure during compaction and elastic stages, initiation and development during the plastic yield stage, and rapid expansion and penetration during the postpeak stage. The analysis helps clarify the coal failure mechanism under triaxial stress.
Article
Geochemistry & Geophysics
Kai Wang, Xiang Zhang, Haijun Guo, Qiang Fu, Dengke Wang, Hang Zhang, Fangchao Lu
Summary: This study reveals the propagation law of hydraulic fractures in the immediate roof of soft outburst coal seam and the changes in microstructure after hydraulic fracturing. Experimental results show that the bedding angle significantly affects the extension of hydraulic fractures, which are determined by both internal fractures and the cementation strengths of the bedding planes. The findings provide guidance for the design and application of hydraulic fracturing in the immediate roof of soft outburst coal seam.
