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Dynamic characteristics of coal specimens with varying static preloading levels under low-frequency disturbance load

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Journal of Central South University 2024年第8期31卷 2644-2657页

作者： Wen, Xiao-ze Feng, Guo-rui Guo, Jun Yu, Lu-yang Qian, Rui-peng Zhang, Jie Zhang, Peng-fei Feng, Wen-ming College of Mining Engineering Taiyuan University of Technology Taiyuan China key laboratory of shanxi Province for mine rock strata control and disaster prevention Taiyuan University of Technology Taiyuan China State key laboratory of Hydroelectric and Engineering Tsinghua University Beijing China

The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces. This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system, and studied the strength evolutions, surface deformations, acoustic emission (AE) characteristic parameters, and the failure modes of coal specimens with different static preloading levels were studied. The disturbance damage is positively correlated with the coal specimen static preload level. Specifically, the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60% and 70% of the uniaxial compressive strength (UCS) were 2.66 and 3.19 times that of the 50% UCS specimens, respectively. Macroscopically, this behaviour manifested as a decrease in the compressive strength, and the mean strengths of the disturbance-damaged coal specimens with 60% and 70% of UCS static preloading decreased by 8.53% and 9.32%, respectively, compared to those of the specimens under pure static loading. The crack sources, such as the primary fissures, strongly control the dynamic response of the coal specimen. The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.

关键词： low-frequency disturbance dynamic response coal specimens static preloading level

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Stability analysis of longwall top-coal caving face in extra-thick coal seams based on an innovative numerical hydraulic support model

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International Journal of Mining Science and Technology 2024年第4期34卷 491-505页

作者： Jun Guo Wenbo Huang Guorui Feng Jinwen Bai Lirong Li Zi Wang Luyang Yu Xiaoze Wen Jie Zhang Wenming Feng College of Mining Engineering Taiyuan University of TechnologyTaiyuan 030024China key laboratory of shanxi Province for mine rock strata control and disaster prevention Taiyuan University of TechnologyTaiyuan 030024China shanxi Coking Coal Group Co. Ltd.Taiyuan 030024China shanxi-Zheda Institute of Advanced Materials and Chemical Engineering Taiyuan 030024China

The relationship between support and surrounding rock is of great significance to the control of surrounding rock in mining *** view of the fact that most of the existing numerical simulation methods construct virtual elements and stress servo control to approximately replace the hydraulic support problem,this paper establishes a new numerical model of hydraulic support with the same working characteristics as the actual hydraulic support by integrating numerical simulation software Rhino,Griddle and FLAC3D,which can realize the simulation of different working *** on this model,the influence mechanism of the supporting strength of hydraulic support on surrounding rock stress regulation and coal stability in front of the top coal caving face in extra thick coal seam were ***,under different support intensity,the abutment pressure of the bearing coal and the coal in front of it presents the “three-stage”evolution *** influence range of support intensity is 15%–30%.Secondly,1.5 MPa is the upper limit of impact that the support strength can have on the front coal failure ***,within a displacement range of 2.76 m from the coal wall,a support strength of1.5 MPa provides optimal control of the horizontal displacement of the coal.

关键词： Extremely thick coal seam Fully mechanized top coal caving Support strength Support-surrounding rock interaction

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Failure mechanisms and destruction characteristics of cemented coal gangue backfill under compression effect of non-uniform load

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Journal of Central South University 2024年第8期31卷 2676-2693页

作者： Feng, Guo-rui Guo, Wei Qi, Ting-ye Li, Zhu Cui, Jia-qing Wang, Hao-chen Cui, Ye-kai Ma, Jing-kai College of Mining Engineering Taiyuan University of Technology Taiyuan China shanxi Province Research Center of Green Mining Engineering Technology Taiyuan China shanxi Province Coal-based Resources Green and High-efficiency Development Engineering Center Taiyuan China shanxi key laboratory of mine rock strata control and disaster prevention Taiyuan China

Backfill mining is one of the most important technical means for controlling strata movement and reducing surface subsidence and environmental damage during exploitation of underground coal resources. Ensuring the stability of the backfill bodies is the primary prerequisite for maintaining the safety of the backfilling working face, and the loading characteristics of backfill are closely related to the deformation and subsidence of the roof. Elastic thin plate model was used to explore the non-uniform subsidence law of the roof, and then the non-uniform distribution characteristics of backfill bodies’ load were revealed. Through a self-developed non-uniform loading device combined with acoustic emission (AE) and digital image correlation (DIC) monitoring technology, the synergistic dynamic evolution law of the bearing capacity, apparent crack, and internal fracture of cemented coal gangue backfills (CCGBs) under loads with different degrees of non-uniformity was deeply explored. The results showed that: 1) The uniaxial compressive strength (UCS) of CCGB increased and then decreased with an increase in the degree of non-uniformity of load (DNL). About 40% of DNL was the inflection point of DNL-UCS curve and when DNL exceeded 40%, the strength decreased in a cliff-like manner; 2) A positive correlation was observed between the AE ringing count and UCS during the loading process of the specimen, which was manifested by a higher AE ringing count of the high-strength specimen. 3) Shear cracks gradually increased and failure mode of specimens gradually changed from “X” type dominated by tension cracks to inverted “Y” type dominated by shear cracks with an increase in DNL, and the crack opening displacement at the peak stress decreased and then increased. The crack opening displacement at 40% of the DNL was the smallest. This was consistent with the judgment of crack size based on the AE b-value, i.e., it showed the typical characteristics of “small b-value-large crack and

关键词： cemented coal gangue backfill crack opening displacement degree of non-uniformity of load failure mode non-uniform load

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Compressive performance of innovative reinforced pillars in closed/abandoned mines

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Journal of Central South University 2024年第8期31卷 2780-2793页

作者： Li, Jian Bai, Jin-wen Feng, Guo-rui Wang, Shan-yong Zhao, Hong-chao Mi, Jia-chen Pan, Rui-kai Shi, Xu-dong Ma, Jun-biao College of Mining Engineering Taiyuan University of Technology Taiyuan China key laboratory of shanxi Province for mine rock strata control and disaster prevention Taiyuan University of Technology Taiyuan China shanxi-Zheda Institute of Advanced Materials and Chemical Engineering Taiyuan China Priority Research Centre for Geotechnical Science and Engineering School of Engineering The University of Newcastle Callaghan Australia School of Geology and Mining Engineering Xinjiang University Urumqi China Department of Mining Engineering Shanxi Institute of Energy Jinzhong China

Pillar is closely related to the stability and reliability of underground spaces in closed/abandoned mines. The present research introduced a new technique to strengthen square cement mortar columns via fiber-reinforced polymer (FRP) strips to verify the strengthening effect of FRP on pillars. Compared to a fully wrapped FRP jacket, the advantages of FRP strip are cost-effective and easy-to-construct. A series of compression tests as well as theoretical analysis were carried out to explore the mechanical behavior of square cement mortar specimens partially strengthened with FRP strips. The results verified the effectiveness of FRP strips in enhancing the stress and strain of cement mortar. Different from unconfined cement mortar specimens, these FRP-strengthened cement mortar specimens are featured with the double-peaked behaviors, mainly attributed to the stress state transformation from a one-dimensional to a three-dimensional stress state. It also indicated that the enhancement of stress increased with the FRP strip width. Moreover, the brittle-ductile transition ductile failure characteristics were also observed in FRP-confined cement mortar specimens. The ultimate ductility of the cement mortar specimen decreases gradually with the growth of the FRP strip width. The main contribution of this research is to enrich the strengthening techniques for residual pillars.

关键词： brittle-ductile transition double-peaked behaviors fiber-reinforced polymer partially strengthening uniaxial compression

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Visualization and characterization of experimental hydraulic fractures interacting with karst fracture-cavity distributions

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Journal of rock Mechanics and Geotechnical Engineering 2024年第5期16卷 1667-1683页

作者： Hanzhi Yang Xin Chang Chunhe Yang Wuhao Guo Lei Wang Guokai Zhao Yintong Guo State key laboratory of Coal mine disaster Dynamics and control Chongqing UniversityChongqing400044China State key laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and *** fracturing is considered as the best method for exploiting carbonate reservoirs;however,previous studies primarily focused on the effects of individual types of geological formations,such as natural fractures or cavities,on fracture *** this study,true-triaxial physical simulation experiments were systematically performed under four types of stress difference conditions after the accurate prefabrication of four types of different fracture-cavity distributions in artificial ***,the interaction mechanism between the hydraulic fractures and fracture-cavity structures was systematically analyzed in combination with the stress distribution,cross-sectional morphology of the main propagation path,and three-dimensional visualization of the overall fracture *** was found that the propagation of hydraulic fractures near the cavity was inhibited by the stress concentration surrounding the *** contrast,a natural fracture with a smaller approach angle(0°and 30°)around the cavity can alleviate the stress concentration and significantly facilitate the connection with the *** addition,the hydraulic fracture crossed the natural fracture at the 45°approach angle and bypassed the cavity under higher stress difference conditions.A new stimulation effectiveness evaluation index was established based on the stimulated reservoir area(SRA),tortuosity of the hydraulic fractures(T),and connectivity index(CI)of the *** findings provide new insights into the fracturing design of carbonate reservoirs.

关键词： Karst fracture-cavity reservoir Fracturing experiment Fracture propagation Cross-sectional morphology Stimulation effectiveness

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低频扰动下不同预静载水平煤样动态响应特征（英文）

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Journal of Central South University 2024年第8期 2644-2657页

作者：文晓泽冯国瑞郭军于露杨钱瑞鹏张洁张鹏飞冯文明 College of Mining Engineering Taiyuan University of Technology key laboratory of shanxi Province for mine rock strata control and disaster prevention Taiyuan University of Technology State key laboratory of Hydroelectric and Engineering Tsinghua University

开采扰动影响下残采区遗留煤柱的力学特性对遗煤资源复采的安全性有重要影响。为了明晰低频扰动(5 Hz，正弦波)下不同预静载水平煤样的动态响应特征，基于自主研发的动静载耦合电液伺服试验机，开展了低频扰动荷载作用下不同预静载水平... 详细信息

开采扰动影响下残采区遗留煤柱的力学特性对遗煤资源复采的安全性有重要影响。为了明晰低频扰动(5 Hz，正弦波)下不同预静载水平煤样的动态响应特征，基于自主研发的动静载耦合电液伺服试验机，开展了低频扰动荷载作用下不同预静载水平煤样的动态单轴压缩试验；同时采用数字图像相关技术及声发射设备对煤样破裂过程进行监测。结果表明，低频扰动损伤与煤样的预静载水平成正比，预静载水平为60%单轴抗压强度(UCS)和70%UCS组煤样的累计声发射(AE)计数率是50%UCS组的2.66和3.19倍；宏观上表现为扰动损伤煤样强度的劣化，预静载水平为60%UCS和70%UCS的扰动损伤煤样强度相较纯静态加载分别降低了8.53%和9.32%。此外，低频扰动荷下煤样的不可逆应变较小，但是强度劣化较大，与致密硬岩的动态响应差异显著。内部随机分布的原生裂隙等裂纹源对煤样扰动损伤和动态力学响应特征有明显的控制作用。

关键词：低频扰动动态响应煤样静态预应力水平

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Dynamic response characteristics of muddy sandstone in pumped storage mine under action of high-stress dynamic disturbance

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Journal of Central South University 2024年第8期31卷 2736-2747页

作者： Liang, Bin Wang, Dong Luan, Heng-jie Dong, Ling Liu, Jian-kang Wang, Chang-sheng State key laboratory of Mining disaster prevention and control Co-Founded by Shandong Province and the Ministry of Science and Technology Shandong University of Science and Technology Qingdao China

During the construction and operation of the abandoned mine pumped storage power station, the underground space surrounding rock body faces the complex stress environment under the action of mining disturbance, frequent pumping, water storage and other dynamic disturbances. The stability of the abandoned mine surrounding rock body is the basis for guaranteeing the safety and effectiveness of water storage in the underground space of the abandoned mine. By considering the two main factors of different stress levels and disturbance amplitudes, the mechanical properties, damage characteristics and acoustic emission characteristics of the abandoned mine perimeter rock body under dynamic disturbance were investigated using a creep-disturbed dynamic impact loading system. The experimental results show that: 1) The stress level is considered to be the major contributing factor of the failure of muddy sandstone, followed by the amplitude of the disturbances; 2) The time required for the destruction of muddy sandstone decreases with the increase of amplitude. When the stress level is 80%, the sandstone specimens have a decreasing number of cycles as the disturbance amplitude increases. The disturbance amplitude is sequentially increased from 4 MPa to 5, 6, 7, and 8 MPa, the number of cycles required for specimen destruction decreases significantly by 96.71%, 99.13%, 99.60%, and 99.93%, respectively; 3) Disturbance amplitude and stress level have a significant effect on muddy sandstone damage and damage occurs only after a certain threshold is reached. With the increase of stress level and disturbance amplitude, the macroscopic damage of muddy sandstone is mainly conical, with obvious flake spalling and poor damage integrity; 4) According to the time-dependent changes in AE energy and ringing counts, the acoustic emission activity during the failure process could be divided into three phases, namely, weakening period, smooth period, and surge period, corresponding to the comp

关键词： abandoned mine pumped storage dynamic disturbance muddy sandstone acoustic emission

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Experimental investigation of dynamic characteristics of leaching tubing for solution mining of salt cavern carbon and energy storage

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Petroleum Science 2024年第4期21卷 2703-2722页

作者： Yin-Ping Li Xin-Bo Ge Xi-Lin Shi Hong-Ling Ma State key laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil Mechanics Chinese Academy of Sciences University of Chinese Academy of Sciences College of Energy and Mining Engineering Shandong University of Science and Technology State key laboratory of Mining disaster prevention and control Co-founded by Shandong Province and the Ministry of Science and Technology Shandong University of Science and Technology

Salt caverns are extensively utilized for storing various substances such as fossil energy, hydrogen,compressed air, nuclear waste, and industrial solid waste. In China, when the salt cavern is leached through single-well water solution mining with oil as a cushion, engineering challenges arise with the leaching tubing, leading to issues like damage and instability. These problems significantly hinder the progress of cavern construction and the control of cavern shape. The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space, which results in severe bending or damage to the tubing. This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus. The experiment utilizes a silicone-rubber pipe(SRP) and a polycarbonate pipe(PCP) to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid. These factors include external space constraint, flexural rigidity, medium outside the pipe, overhanging length, and end conditions. The experiments reveal four dynamic response phenomena: water hammer, static buckling, chaotic motion, and flutter instability. The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid. Additionally, the flutter critical flow velocity is influenced by the end conditions and different external media.

关键词： Salt cavern storage Solution mining Leaching tubing Experimental investigation Flutter instability

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Paradigm for Determining the Optimal Ultradeep and Superthick Saline Aquifer for High-TDS mine Water Geological Storage

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Acta Geologica Sinica(English Edition) 2024年第3期98卷 771-785页

作者： LI Xin CHEN Ge XU Zhimin LIU Qi CHEN Tianci SUN Yajun School of Resources and Geosciences China University of Mining and TechnologyXuzhouJiangsu 221116China National Professional Central laboratory of Basic Research on mine Water disaster prevention and control Technology XuzhouJiangsu 221116China

Saline aquifers are the most popular waste and CO_(2)injection and storage reservoirs *** project proposes that several optimal injection positions should be investigated as hydraulic pressure-focused positions,in order to relieve the high demands of pump *** comprehensive indices(F_(i))representing the injectivity of different burial depths were obtained by using information entropy,based on the mercury injection experimental data of 13 rock *** results demonstrated that the burial depths of No.4,No.1 and No.2 in the Liujiagou Formation were the most suitable positions for hydraulic focused injection,which means the upper 30 m thickness could be regarded as the hydraulic focused range in the saline aquifer with an average thickness of 400 *** addition,some laboratory experiments and in situ tests were carried out for the purpose of certifying and analyzing results,including SEM,XRD,brittleness index and *** results suggested that the rock samples at the No.4,No.1 and No.2 burial depth ranges have loose microstructure,weak cementation,as well as dual pores and *** lithology is mainly quartz and feldspar,but the clay mineral content is high(10%-25%),which is positive for *** lithology is suitable for hydraulic fracturing to form extended cracks and micro-fissures during high-TDS(total dissolved solids)mine water injection,because of the high brittleness ***,a theoretical and technical framework for high-TDS mine water injection was established,based on operating pilot *** theoretical defects and drawbacks learned from the field practices were summarized and solutions *** research in this study could provide guidance and a paradigm for the inexpensive treatment of high-TDS mine water by injection and storage.

关键词： ultradeep Liujiagou Formation high-TDS mine water optimal hydraulic injection positions information entropy reservoir spatial characteristics

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A novel nano-grade organosilicon polymer:Improving airtightness of compressed air energy storage in hard rock formations

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International Journal of Mining Science and Technology 2024年第3期34卷 305-321页

作者： Zhuyan Zheng Guibin Wang Chunhe Yang Hongling Ma Liming Yin Youqiang Liao Kai Zhao Zhen Zeng Hang Li Yue Han Institute of rock and Soil Mechanics Chinese Academy of SciencesWuhan 430071China University of Chinese Academy of Sciences Beijing 100049China State key laboratory of Geomechanics and Geotechnical Engineering Wuhan 430071China State key laboratory of Coal mine disaster Dynamics and control Chongqing UniversityChongqing 400044China PowerChina Huadong Engineering Corporation Limited Hangzhou 310014China

Enhancing cavern sealing is crucial for improving the efficiency of compressed air energy storage(CAES)in hard rock *** study introduced a novel approach using a nano-grade organosilicon polymer(NOSP)as a sealant,coupled with an air seepage evaluation model that incorporates Knudsen ***,the initial coating application methods were outlined,and the advantages of using NOSP compared to other sealing materials,particularly regarding cost and construction techniques,were also examined and *** results indicated a significant reduction in permeability of rock specimens coated with a 7–10μm thick NOSP ***,under a 0.5 MPa pulse pressure,the permeability decreased to less than 1 n D,and under a 4 MPa pulse pressure,it ranged between4.5×10^(-6)–5.5×10^(-6)m D,marking a 75%–80%decrease in granite *** sealing efficacy of NOSP surpasses concrete and is comparable to rubber *** optimal viscosity for application lies between 95 and 105 KU,and the coating thickness should ideally range from 7 to 10μm,applied to substrates with less than 3%*** study provides new insights into air transport and sealing mechanisms at the pore level,proposing NOSP as a cost-effective and simplified solution for CAES applications.

关键词： Compressed air energy storage Lining Permeability Transient pulse method Hard rock cavern Nano-grade organosilicon polymer coating

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