循环载荷作用下饱水灰岩力学性能及能量演化规律研究

Mechanical Properties and Energy Evolution of Saturated Limestone Under Cyclic Load

为了探究水力耦合作用下煤层底板石灰岩的力学特性及变形规律,预防因工程扰动而产生的底板失稳破坏,利用岩石微机伺服多场耦合试验系统,开展了不同围压下饱水灰岩的常规三轴压缩试验及循环加卸载试验。通过经典岩石力学理论划分了岩石全应力-应变曲线的各个阶段,从能量耗散及累积损伤的角度,对循环载荷作用下的岩石破坏机理进行研究。研究发现:(1)在围压不变的条件下,循环加卸载试验下岩样的峰值强度较常规三轴压缩试验有所降低,整体应变量随卸荷水平的增加而变大,扩容现象逐渐显著;(2)在围压及循环载荷作用条件下,饱水灰岩的破坏形式主要为剪切破坏,当围压增大后,逐渐出现了以横向、纵向为主的张拉破坏;(3)随着循环等级的增加,弹性应变能的占比相应降低,耗散能的占比逐渐增大,同一循环等级下,随着循环次数的增加,耗散能占比呈小幅降低趋势;(4)扩大卸荷水平,岩石损伤行为越发活跃,但同等级循环内岩石损伤出现小幅度降低,与耗散能的演化规律及机理基本一致。

In order to study the mechanical properties and deformation laws of limestone in coal seam floor under hydraulic coupling and to prevent the instability and failure of coal floor caused by engineering disturbance,the conventional triaxial compression test and cyclic loading and unloading test of saturated limestone under different confining pressures were carried out based on rock microcomputer servo multi-field coupling system.The stages of total stress-strain curve of rock were divided by classical rock mechanics theory.The failure mechanism of rock under cyclic load was studied from the view of energy dissipation and cumulative damage.The study findings are as follows.Firstly,under the condition of constant confining pressure,the peak strength of rock sample under cyclic loading and unloading test is lower than that of conventional triaxial compression test,and the overall strain variable increases with the increase of unloading level,and the dilatancy phenomenon is gradually significant,Secondly,under confining pressure and cyclic load,shear failure is the main failure mode of saturated limestone.When confining pressure increases,transverse and longitudinal tensile failure occurs gradually.Thirdly,with the increase of cycle level,the proportion of elastic strain energy decreases correspondingly,and the proportion of dissipated energy increases gradually.Under the same cycle level,with the increase of cycle number,the dissipated energy shows a slight decrease trend.Finally,with the increase of unloading level,the rock damage behavior becomes more active,but there is a slight decrease in rock damage within the same cycle level,which is basically consistent with the evolution law and mechanism of dissipated energy.