干湿循环下溶隙灰岩单轴压缩损伤破裂特征

Effect of Dry-Wet Cycles on Damage and Failure Characteristics ofKarst-fissured Limestone under Uniaxial Compression

为研究干湿循环对溶隙灰岩损伤破坏特征的影响,制备裂隙状、椭圆状、蘑菇状和类哑铃状溶隙灰岩试样,开展单轴压缩试验并辅以数字图像相关方法(DIC)和声发射技术进行监测,分析0、3、6、10次干湿循环下溶隙灰岩的损伤特性和变形破裂特征。结果表明:①基于峰值强度定义干湿循环和溶隙形状损伤度,干湿循环损伤度与循环次数和水-岩接触面积成正比,溶隙形状损伤度在干湿循环过程中为33.31%~64.86%;耦合损伤度合理表达了二者的耦合关系。②干湿循环作用下溶隙灰岩由拉伸破坏转变为以拉伸破坏为主的拉剪混合破坏,表面应变局部化带过渡到“延性”扩展;而溶隙形状对试样破坏有优势导向作用。③干湿循环导致岩样声发射累积振铃计数减小,裂纹起裂应力σci及裂纹损伤应力σcd也逐步降低。研究成果可以为三峡库区溶隙灰岩的破坏机理分析提供科学依据。

To investigate the impact of dry-wet cycles on damage and failure characteristics of karst-fissured limestone,we prepared limestone specimens with fracture-shaped,elliptical,mushroom-shaped,and dumbbell-shaped karst fissures for uniaxial compression test.Digital Image Correlation and Acoustic Emission techniques were also employed to monitor the damage and deformation characteristics of karst-fissured limestone after 0,3,6 and 10 dry-wet cycles.The results showed that the dry-wet cycles and the karst fissure damage degree of limestone samples were defined based on the peak strength.The damage degree was proportional to the number of cycles and the water-rock contact area,ranging from 33.31%to 64.86%during dry-wet cycles.We expressed the coupling relationship between the damage degree of karst fissure and the dry-wet cycle.Under dry-wet cycles,the failure mode of karst-fissured limestone changed from tensile failure to tensile-shear mixed failure,and the local zone of surface strain transitioned to ductile extension.The shape of karst fissure had a dominant guiding effect on the failure path.In addition,the cumulative ringing counts of acoustic emission,as well as the crack initiation stressσci and crack damage stressσcd decreased with the proceedings of dry-wet cycles.The research results provide scientific basis for analyzing the failure mechanism of karst-fissured limestone in the Three Gorges Reservoir area.