分级加载条件下深部灰岩蠕变试验及模型

Creep Experiment and Model of Deep Limestone Under Step Loading

通过对矿山深部灰岩开展分级加载单轴蠕变试验,获取了不同应力水平下轴向和径向蠕应变,基于试验结果,分析各分级应力水平下轴向蠕应变、径向蠕应变和体应变的变化规律,研究轴向和径向蠕应变与各分级总应变的比值关系,并将该比值依次定义为蠕变效应比K_z、K_h,二者之差为K_(h-z)。研究发现:随着应力水平的提高,各分级轴向和径向蠕应变均先增加后减小;当恒载应力小于51 MPa时,试样体积压缩,K_(h-z)在±0.28%范围内,表明轴向蠕变与径向蠕变效应彼此相当;当超过该应力水平后,试样扩容,K_z和K_h剧增,K_(h-z)由0.21%突增至2.64%,在试样发生蠕变破坏时达到峰值,表明与轴向蠕变相比,在扩容阶段径向蠕变效应更加明显。选用西原体模型来描述灰岩轴向蠕变特性,通过曲线拟合的最小二乘法求取蠕变模型参数,R^2均值为0.931,拟合效果较好。

The uniaxial creep test with step loading is carried out for the deep limestone, the axial and radial creep strain of different stress levels are obtained.Based on the test results, the change laws of axial creep strain, radial crcep strain and volumetric strain under different stress levels are analyzed.In addition to, the ratios of the axial and radial creep strain to the total strain are studied, which are defined as the ratio of creep effect Kz and Kh, and the difference between those is Kh-z.The study found that with the increase of the stress level, the axial creep strain and radial creep strain increase first and then decrease.When the constant stress is less than 51 MPa, the sample volume is compressed, Kh-z are within the scope of ±0.28%.It shows that the axial creep effect and radial creep effect are equal.However,if the stress is exceeded,the sample will expand and kz,kh increase rapidly,kh-z increased from 0.21% to 2.64%.It will reach peak value when the creep failure of specimen occurs.The results show that the radial creep effect is more obvious in the expansion stage, compared with the axial creep.The fitting effect is better by describing the characteristics of limestone axial creep with visco-elastoplastic model, and use the method of least squares curve fitting to get the creep model parameters, the average value of R2 is 0.931.