水力作用下砂岩三轴卸荷试验及破裂特性研究

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高应力、高水压卸荷条件下岩石的非连续性微缺陷演化过程研究对揭示隧道围岩裂纹的起裂孕育、碎胀裂化和峰值破坏,分析围岩稳定性具有重要意义。利用MTS815型程控伺服刚性试验机开展了砂岩在固定围压、不同水压条件下的水力三轴卸荷试验。试验结果表明:岩石变形在卸荷前以压缩为主,变化微小;卸荷后不久开始快速扩容,直至损伤破裂。水力条件下应力–应变曲线上的各个特征应力值比无水压条件下的饱和试样有不同程度地提高,增加了应变能储备,从初始扩容到峰值强度的历时更短,曲线斜率更陡。随着水压的不断增大,各个特征应力值有所减小,表现在起裂条件降低,压缩极限减小,扩容时间提前,表明了砂岩在高水压条件下的脆性特性进一步增强,抵抗变形破坏的能力逐渐降低。通过扩容特征值与扩容点后的体应变关系,求得初始扩容点后的相对扩容应变与变形模量差,建立了多项式回归关系。研究结论揭示了水力作用下砂岩扩容变形行为的强烈性和突发性,可为水–力双场条件下的围岩变形预测及控制提供参考。 The study of rock discontinuity evolution process under high stress and high hydraulic pressure unloading is of great significance for revealing the initiation and rupture, cracking and cracking of surrounding rock and the analysis of the stability of surrounding rock. Hydraulic triaxial unloading test of sandstone under fixed confining pressure and different water pressure conditions was carried out by MTS815 program-controlled servo rigid testing machine. The experimental results show that the deformation of rock is dominated by compression before the unloading, and the change is slight. The unloading quickly begins to expand rapidly until the damage ruptures. Under hydraulic conditions, the stress of each characteristic stress on the stress-strain curve is increased to some extent than that of the saturated sample under no water pressure, which increases the strain energy reserve, and the duration from the initial expansion to the peak intensity is shorter and the slope of the curve is steeper . With the increasing of water pressure, the stress of each characteristic decreases, which shows that the condition of initiation of cracking decreases, the compression limit decreases and the expansion time advances. It shows that the brittleness of sandstone under high water pressure is further enhanced, Deformation and destruction of ability to gradually reduce. Through the relationship between the volumetric eigenvalue and the body strain after the expansion point, the relative expansion strain and deformation modulus difference after the initial expansion point are obtained, and the polynomial regression relationship is established. The conclusion of the study reveals the strong and sudden deformation of sandstone under the action of hydraulic stress. It can provide a reference for the prediction and control of the surrounding rock deformation under the conditions of water-power and double-field.
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