摘要
为探讨深埋软岩在不同应力路径下力学性质的差异,对取自丹巴水电站右岸平硐深埋软岩分别进行室内三轴加载试验和不同围压等级、不同卸荷应力水平、不同卸荷速率的恒轴压卸围压试验,并对岩样卸荷破坏面进行微观形貌扫描,分别探讨不同条件下岩样的变形、强度及破坏特征,结果发现:(1)相比三轴加载试验,同等级围压的软岩在卸荷条件下的强度、峰值应变及力学参数都有减小,应力–应变曲线从延性向脆性转换;(2)软岩峰值轴向应变、极限强度、残余强度与卸荷应力水平、卸荷速率均呈正相关性;(3)相比Hoek-Brown经验强度准则,Mohr-Coulomb强度准则能更好地描述软岩强度特性,不同应力路径对抗剪强度参数影响有差异性,卸荷速率对c值的影响更为显著,而卸荷应力水平对?值的影响更为显著;(4)软岩加、卸载条件下都发生剪切破坏,加载时除主裂纹外基本没有衍生微裂纹,卸载时,低卸荷应力水平下岩样破坏后的次生裂纹更发育,且卸荷速率越大岩样破坏程度越强烈;低围压下卸荷破坏时,岩石断面微观形貌演化自由度较高,破坏面粗糙度大。
In order to investigate the difference of mechanical properties of deep-buried soft rock under different stress paths,the indoor triaxial loading test and confining pressure unloading test with a constant axial stress under different confining pressure levels,different unloading stress levels and different unloading rates were performed on the deep-buried soft rock samples from the right bank of the Danba Hydropower Station, and the microtopography of the unloading failure surface of the rock samples was scanned. Deformation,strength and failure characteristics of rock samples under different conditions were discussed. The results show that,compared with the triaxial loading test,the strength and the peak strain the soft rock with the same grade confining pressure under the unloading condition are reduced,and the stress-strain curve is converted from ductility to brittleness. The peak axial strain,the ultimate strength and the residual strength of the soft rock are positively correlated to the unloading stress level and the unloading rate. Compared with the Hoek-Brown empirical strength criterion,the Mohr-Coulomb strength criterion can better describe the soft rock strength characteristics. Different stress paths have different effects on the shear strength parameters. The unloading rate has a more significant effect on c value while the unloading stress level has a more significant effect on ? value. The failure mode of soft rock under both loading and unloading is shear failure. There is no derivatized microcrack except for the main crack under loading,but the low unloading stress level is more likely to induce new cracks than the high unloading stress level. The larger the unloading rate,the more severe the damage is. When the sample fails under a lower confining pressure unloading,there is a higher degree of freedom of failure surface microtopography evolution and the roughness of the failure surface is larger.
引文
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