摘要
运用自主研制的煤岩热-流-固耦合试验系统,以原煤为研究对象,进行峰后轴压保持在不同应力水平下围压的卸载试验,以分析围压卸载对原煤变形特性和渗透特性的影响。研究结果表明:通过径向应变ε_3、轴向应变ε_1和体应变ε_V的不可恢复变形量以及三者在力加载过程中的响应程度来定义损伤变量,满足损伤变量的变化区间[0,1],并以此计算煤样在卸载过程中的损伤量,得到在峰后轴压σ_1保持不变,对围压σ_3进行卸载时,损伤量D随着σ_3的减小而增大,煤样的损伤程度越来越大;当轴压卸荷到不同应力时,煤样的渗透率随围压卸载次数的增加而增大,表明当σ_1减小时,σ_3对渗透率的影响越来越重要,同时煤样内部的孔隙裂隙以发育、扩展、延伸为主。此外,渗透率k在σ_3卸载初期,几乎不增加;当σ_3继续卸载时,k开始增大,并且斜率越来越大,表明煤样的损伤加剧。当保持σ_1不变,对σ_3进行卸载时,相当于摩尔应力圆半径增大,煤样向破坏的趋势发展,发生二次破坏的可能性增大。随着σ_3的卸载,卸围压前σ_1越大,摩尔应力圆半径越大,煤样的承载能力就越弱,更易发生煤样的二次破坏,表现在煤样的轴向应变ε_1和径向应变ε_3发生突变。
In this study, experiments were conducted on raw coal specimens by using the self-developed triaxial servo-controlled seepage equipment for thermo-hydro-mechanical coupling of coal containing methane. Experiments were carried out when the axial pressure maintained at different stress levels but the confining pressure was unloaded. We studied the effects of unloading confining pressure on deformation properties and permeability characteristics of gas-filled coal at the post-peak. The results showed that the damage variable was defined by the unrecoverable deformations of radial strain ε3, axial strain ε1 and volumetric strain εV and the response of these three parameters during the process of unloading. The interval [0, 1] of damage variable was satisfied to calculate the damage quantity of coal specimen in the process of unloading. When the axial pressure σ1 remained constant and the confining pressureσ3 was unloaded, the amount of damage quantity D increased with the decrease of σ3 and the damage degree of coal specimen increased greatly. When unloading the axial pressure to different stress levels, the permeability of coal specimen increased with the growing unloading times of confining pressure. It indicated that the influence of confining pressure σ3 on permeability was more and more important when σ1 decreased. At the same time, the pores and fractures in the coal specimen were developed, expanded and extended. In addition, the permeability k hardly increased at the beginning of unloadingσ3. As σ3 continued to unload, k began to increase and the slope became growing, indicating the severe damage of coal specimen. The radius of Mohr stress circle was equivalent to an increase under this stress path of loading and unloading, and coal specimens tended to destruction causing the increasing possibility of the occurrence of secondary failure. At the higher level of σ1, with the unloading of σ3, the radius of Mohr stress circle increased and the supportability of coal specimens became weaker. Hence, the secondary failure easily occurred, which manifested the abrupt change of axial strain ε1 and radial strain ε3.
作者
刘超
张东明
尚德磊
赵宏刚
宋真龙
俞欢
LIU Chao;ZHANG Dong-ming;SHANG De-lei;ZHAO Hong-gang;SONG Zhen-long;YU Huan(State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, China;College of Resources and Environmental Sciences, Chongqing University, Chongqing 400030, China;State and Local Joint Engineering Laboratory of Methane Drainage in Complex Coal Gas Seam, Chongqing 400030, China)
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2018年第6期2017-2024,2034,共9页
Rock and Soil Mechanics
基金
国家自然科学基金(No.51434003
No.51374256)~~
关键词
围压卸载
损伤
损伤变量表达式
渗透率
摩尔应力圆
二次破坏
confining pressure unloading
damage
damage variable expression
permeability
Mohr stress circle
secondary failure
