循环荷载作用下围压对砂岩滞回环演化规律的影响

EFFECT OF CONFINING PRESSURE ON EVOLUTION LAW OF HYSTERESIS LOOP OF SANDSTONE UNDER CYCLIC LOADING

利用MTS815岩石力学试验系统对砂岩进行循环荷载作用下不同围压时的三轴压缩试验,研究循环荷载作用下围压对砂岩滞回环演化规律的影响。试验结果表明:(1)可将滞回环分为加载段和卸载段分别进行二次拟合。在加载段,随着循环次数的增加,拟合参数A,B随围压的增大而增大,而拟合参数C随围压的增大而减小,拟合曲线的开口均逐渐增大并趋于稳定,且围压越大,其达到稳定的时间越短;在卸载段,随着循环次数的增加,拟合参数A随围压的增大而减小,拟合参数B,C随围压的增大呈现减小的趋势,拟合曲线的开口逐渐增大并趋于稳定,且围压越大,其拟合曲线的开口越大。(2)随着围压的增加,砂岩的滞回环面积增大,这说明随着围压的增加,试件在每个循环中所耗散掉的能量也在增加,即裂纹扩展所需要的能量也会随着围压的增加而增加。(3)分析试验参数和拟合曲线,得出轴向单位体积耗散能与循环次数的关系符合乘幂负指数关系,曲线的特征是随着循环次数的增加,轴向单位体积耗散能衰减很快,逐渐达到稳定。

The effect of confining pressure on evolution law of hysteresis[l1] loop of sandstone under cyclic loading is investigated by using MTS815 rock mechanics testing system. Test results are shown as follows：（1） The hysteresis [l2]loop can be divided into two parts to perform quadratic fitting. In cyclic loading section,with the increase in cycle,fitting parameters A and B increase with the increase in confining pressure;while the fitting parameter C decreases with the increase in confining pressure. The opening of fitting curve increases gradually and tends to be stable;the greater the confining pressure is,the less the time it need to be stable is. In cyclic unloading section,with the increase in cycle,fitting parameter A decreases with increase in confining pressure;fitting parameters B and C decrease with the increase in confining pressure. The openings of fitting curves increase gradually and tend to be stable;the greater the confining pressure is,the larger the opening of fitting curve is. （2） Hysteresis [l3]loop area of sandstone increases with the increase in confining pressure,which means that with the increase in confining pressure,the dissipation energy of specimen in each cycle increases and the crack propagation energy needed also increases. （3） The relationship between the axial dissipation energy and cycle accords with the power of negative exponent function under cyclic loading;and the feature of the curve is that with the increase in cycle,the axial dissipation energy per unit volume attenuates quickly and tends to be stable gradually.