摘要
对石灰岩不同围压的三轴压缩过程进行微结构观察,发现:当平均应力与体积应变曲线偏离静水压力线时,岩样微结构产生颗粒之间胶结物破坏,颗粒挤紧,孔隙减小,导致应变硬化,达到剪切增强的压实阶段.继续加载较软的颗粒被挤碎,导致崩塌变软,岩样出现宏观软化现象;同时孔洞表面产生大量平行于最大主应力方向的裂纹,汇聚成核.在低围压(<40 MPa)时,含天然缺陷的岩石中,观测到剪切带的产生,也会在局部缺陷处发生崩塌;随着围压的增加(>150MPa),局部体积崩塌将逐步引发大面积的垮塌.对应岩石试件的屈服行为也由以剪切破坏机制为主,逐渐转变为以体积崩塌压缩机制为主,引起纵向应变迅速增加.当剪切增强压缩继续发展到C*′直到峰值应力前时产生颗粒破裂、移动或旋转,曲线出现转向,岩样发生体积膨胀,同时引起密集声发射活动.峰值应力后,微裂纹串联成裂纹簇开始剪切诱导岩样体积膨胀,导致应力降引起应变软化,同时产生剪切局部化.在没有无序性影响的压缩带发展和传播的数值模拟中,展示了压缩带由样品的上下端面向样品中部逐渐扩展的过程,与Bentheim砂岩切片图显示和AE监测结果是吻合的.通过微观与宏观实验结合的描述方法清楚地展现了剪切带、压缩带、膨胀带的产生机理以及压缩带的发展过程,这里压缩屈服过程即为帽盖模型的形成过程,它是近似椭圆的帽盖模型中的帽子部分.
Micro structure observations were conducted on the triaxial compression experiments of 4limestone under different confining pressures.The results showed that when the average stress-volume strain curves deviated from the hydrostatic pressure line,bonds among particles in the micro structure of rock were crushed.These particles were compacted and pores were reduced,it led to strain hardening of rock and the macro behaviors showed shear-enhanced compaction.Increasing the loads,softer particles were completely crushed and it led to collapse softening.The macro behaviors showed a softening property.At the same time,lots of cracks parallel to the maximum principal stress were generated and nucleated.Under low confining pressures,i.e.lower than 40 MPa,some shear bands were observed in rocks with natural defects,and pore collapse could also be found at local. With the confining pressure increasing and when confining pressures reached to a high value,i.e.150 MPa in the present experiments,local pore collapse would develop to global collapse of sample. The corresponding yield mechanism of rock samples changed from shear failure to volume collapse and compaction,which resulted in rapid increasing of axial strain.When the shear enhanced compaction continued and reached to a critical state,e.g.C＊′in the present paper,particles in rock samples were crushed,moved and rotated until the peak stress.Volume expansions generated in sample,and intensive acoustic emissions（AE）were induced.After the peak,micro cracks nucleated to be crack clusters and made the sample volume expanded.It led to stress drop and strain softening,and shear localization was then formed.Numerical analyses of the evolution of compaction bands were conducted by the disorder affecting method,the process of the compaction band developing from the up and the bottom of the sample to the middle of sample was observed,which agreed well with the SEM photos and AE records of Bentheim sandstone.Therefore,the mechanism of shear band,compaction band,and dilatance band forming and the evolution of compaction band were clearly illustrated by experiments at the micro scale and the macro scale.The process of compression yield covered the forming of cap model in plastic theory,and it was the cap of the cap model with quasi ellipse shape.
出处
《地球物理学进展》
CSCD
北大核心
2015年第4期1926-1934,共9页
Progress in Geophysics
基金
国家自然科学基金资助项目(11472264
11272304
40874093)资助
关键词
微观机制
高孔隙岩石
剪切增强压缩
压缩带的传播
椭圆帽子模型
micro mechanism
high porous rock
shear enhanced compaction
propagation of compaction band
elliptical cap model
