不同卸荷速率下北山花岗岩力学特性试验研究

为探讨在增轴压卸围压的应力路径下不同卸荷速率对甘肃北山花岗岩力学性质的影响,对北山花岗岩进行了不同速率、不同围压条件下的卸荷试验,并与循环加卸载试验强度方面的数据对比分析,研究花岗岩的强度变形特征和破坏特点。研究结果表明:1围压效应明显,峰值强度随实时围压升高而增强;卸荷试验峰值强度包络线在循环加、卸载试验峰值强度包络线上方,且随着卸荷试验速率的升高,岩样峰值承载能力增强。2随着卸荷速率的增加,黏聚力增大,但内摩擦角变化较小且无明显规律;相比循环加卸载试验,卸荷试验的黏聚力降低了8%~20%,内摩擦角提高了9%左右。3随着围压的增加,卸荷试验峰值点至峰后应力跌落点的横向应变增量先减小后增加;不同围压下的卸荷起点至卸荷峰值点的横向应变增量在0.5~2.0 MPa/min卸荷速率区间内有相同的增减趋势。4随着卸荷试验速率的增加,岩样破裂面贯通程度增加;随着围压的升高,主破裂面破裂角增大,且破裂面更加平直。

Experimental Research on the Mechanical Properties of Beishan Granite under Different Unloading Rates

In order to analyze the influence of the stress path of unloading confining pressure meanwhile increasing axial pressure rates on mechanical properties of Beishan granite in Gansu province under different test rates,unloading tests with dif-ferent unloading rates and different confining pressure are carried out to analyze the characteristics of rock strength,deformation behavior and fracture features. Comparison analysis of the unloading tests results and cyclic loading-unloading tests results are conducted to discuss the deformation characteristics and damage feature of granite. The study results show that:①The confining pressure effects is significant, it is increased obviously with the increasing of the real-time confining pressure, the envelop curves of test peak strength of unloading test are above the one of cyclic loading-unloading test,the peak load bearing capacity in increased with the increasing of unloading test rate.②With the increasing of unloading test rate,the cohesion of unloading test is decreased irregularly,compared with the cyclic loading-unloading test,the cohesion of unloading test is reduced by 8%~20%,and the internal friction angle is increased about 9%.③With the increasing of confining pressure,the increment of transverse strain between the peak point and post peak stress drop point of unloading test is decreased and then increased,the increment of transverse strain under the different confining pressure between the unloading starting point and unloading peak point have the uniform increasing and decreasing tendency with in the unloading rate range of (0. 5~2. 0) MPa/min.④With the increasing of unloading rate,the fractured surface becomes more developed,the main,the main fractured surfaces become more straight and the fracture angle is increased with increasing of confining pressure.