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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.
The microstructure observation of the triaxial compression process with different confining pressures of limestone shows that when the mean stress and volume strain curve deviate from the hydrostatic pressure line, the cementitious material between the microstructures of the rock samples is destroyed, the particles are tightened, the pores are reduced, Leading to strain hardening, reaching shear-enhanced compaction stage.Continuous loading of the softer particles was crushed, resulting in the collapse softening and macroscopical softening of the rock samples.At the same time, a large number of cracks were generated on the surface of the pores parallel to the direction of maximum principal stress, Nucleation.Under low confining pressure (<40 MPa), the occurrence of shear band was observed in rocks with natural defects, and collapse occurred at local defects. With the increase of confining pressure (> 150 MPa), local The volume collapse will gradually lead to large-scale collapse.The yield behavior of the corresponding rock specimen is also dominated by the shear failure mechanism and gradually changes to the volume collapse compression mechanism, causing the longitudinal strain to increase rapidly.When the shear enhancement compression continues Development to C * ’until the peak stress before the occurrence of particle rupture, movement or rotation, the curve appears turn, the volume of rock sample expansion, while causing intensive acoustic emission activity.After the peak stress, the micro-cracks in series crack The initial shearing of the tufts induces the volume expansion of the rock specimen, which leads to the stress softening and the shearing localization. In the numerical simulation of the development and propagation of the compressive zone without disordered influence, the compression bands are shown from the top and bottom of the sample The process of gradual expansion towards the middle of the sample is in agreement with the Bentheim sandstone slice and AE monitoring results.The microscopic and macroscopic experiments clearly show the formation mechanism of shear band, compression band, expansion band and compression band The process of compressing and yielding here is the formation of a cap model, which is a hat part of an approximately elliptical cap model.