工程科学与技术2025，Vol.57Issue(4)：89-102,14.DOI:10.12454/j.jsuese.202300932
循环加卸载作用下水浸煤体渐进损伤机理试验研究
Experimental Research on Progressive Damage Mechanism for Water Immersed Coal Under Cyclic Loading and Unloading
摘要
Abstract
Objective The technology of underground coal mine reservoirs has become an effective method for protecting and utilizing mine water resources.Among these,the stability of the coal pillar is critical to the safe operation of underground coal mine reservoirs.The coal pillar is subjected to the long-term and repeated action of various mining stresses.The water-bearing state of the coal pillar varies significantly at different periods of wa-ter storage in coal mine underground reservoirs,and the influence of the long-term and repeated mining stresses also differs accordingly.There-fore,studying the deformation and mechanical characteristics of coal samples under different water content conditions and subjected to cyclic loading and unloading contributes to a better understanding of the coal pillar failure mechanism. Methods Cylindrical standard specimens in three water-containing states,dry,natural,and saturated,were fabricated,respectively.First,the ap-propriate cyclic load was selected for the cyclic loading and unloading test through a preloading test.Then,the uniaxial graded cyclic loading and unloading test was conducted,and the number of cycles at each load level was increased to analyze the complete process of fatigue damage in coal and rock under multiple cyclic loads.The damage characteristics of coal samples were monitored using acoustic emission(AE)equipment,and the pore development of the coal samples was detected using nuclear magnetic resonance(NMR)equipment Results and Discussions The average maximum loads of the dried,natural,and saturated coal samples,measured through the preloading experi-ment,were 32.77,27.69,and 22.45 kN,respectively.Compared to the dried coal samples,the average maximum load of the saturated coal samples decreased by 31.49％,indicating that water deteriorated the strength parameters of the coal samples.The acoustic emission signals of coal samples with varying water content states increased gradually with the number of circulation stages,and the degree of fracture development also increased accordingly.Under the action of cyclic stress,the damage and failure of coal mainly occur when the peak load of each level is reached for the first time.The water-rock interaction exhibited a weakening effect on acoustic emission.Under cyclic stress,water-containing coal samples were prone to stress-induced mutations,resulting in instantaneous damage and destruction to the coal body.In addition,with the in-crease of water content,the number of stress mutations also increased.Under the same load,the damage degree of saturated coal samples was higher,resulting in the further development of internal microfissures and the generation of more acoustic emission signals,which partially coun-teracted the weakening effect of water on the acoustic emission signals.Both natural and saturated coal samples experienced further damage and destruction during the loading and unloading of the third-level cycle,with the saturated coal samples exhibiting a higher degree of damage.After cyclic loading and unloading,the pore number of the dried coal samples increased with the number of cycle stages.After the first two stages of cyclic loading and unloading,the natural and saturated coal samples developed pores with varying diameters,and the number of internal pores in-creased.However,after the third stage of cyclic loading and unloading,the number of medium and micropores significantly decreased.The num-ber of large pores has increased slightly,resulting in an overall decrease in the number of internal pores.During the first-stage cyclic loading pe-riod,dried coal samples primarily showed growth in macropores,while natural and saturated coal samples primarily exhibited growth in micro-pores,though the growth was not substantial.After the loading and unloading of the second-level cycle,the bimodal growth area of the dried coal samples was slightly larger than that observed in the first-level cycle.The number of small and medium pores in the natural and saturated coal samples increased significantly,with the growth in medium pores being slightly higher than that of micropores.The number of micropores in the dried coal samples increased significantly,while the growth in medium pores remained relatively low.After the third-level cycle,the number of micropores and medium-large pores in natural coal samples decreased.In saturated coal samples,the total number of internal pores decreased,whereas the number of medium and large pores increased slightly.In dried coal samples,the number of pores with different diameters continued to increase.Pore changes in water-bearing coal bodies exhibited a low-range trend of"increase-decrease-increase"with increasing cyclic stress.After the loading and unloading of stage Ⅰ and stage Ⅱ cycles,the porosity of each coal sample increased.After stage Ⅲ cycles,the po-rosity of the dried coal sample continued to increase,while that of the natural and saturated coal samples decreased.In addition,the reduction in porosity of the coal sample in its natural water-containing state was greater,by 0.45％.The decrease in the porosity of the saturated coal sample was smaller than that of the natural coal sample.Combined with the T2 spectrum,The number increase of macropores in saturated coal samples is greater,which reduces the porosity decrease.The compressive strength of the dried coal sample after grade Ⅲ cyclic loading and unloading was 14.27 MPa,which was 9.85％lower than the average value before cyclic loading and unloading.The compressive strength of the saturated coal sample was 8.49 MPa,which was 24.87％lower than the average value under initial conditions without cyclic loading and unloading.The strength of the coal samples decreased with the increase in water content and the number of cycles. Conclusions This study reveals the damage and failure mechanisms of coal subjected to hierarchical cyclic loading conditions by analyzing the acoustic emission characteristics and pore evolution patterns of coal samples with different water contents under cyclic loading.关键词
煤柱/水浸煤体/循环加卸载/孔隙变化/渐进损伤Key words
coal pillar/water immersed coal body/cyclic loading and unloading/pore change/damage evolution分类
建筑与水利引用本文复制引用
王方田,汤天阔,张村,窦凤金,魏学谦,孙暖,成家章..循环加卸载作用下水浸煤体渐进损伤机理试验研究[J].工程科学与技术,2025,57(4):89-102,14.基金项目
国家自然科学基金面上项目(52474151 （）
52474161) （）
中国矿业大学研究生创新计划项目(2025WLKXJ031) （2025WLKXJ031）
江苏省研究生科研与实践创新计划项目(KYCX25_2803) （KYCX25_2803）
