分级加载下深部粉砂岩单轴压缩蠕变试验研究

Experimental Study on Uniaxial Compressive Creep of Deep Siltstone under Step Loading

为研究深部硬岩的蠕变特性,采用分级加载方式对深部粉砂岩进行了单轴压缩蠕变试验。试验结果表明,分级加载作用下深部粉砂岩产生瞬时的轴向应变和侧向应变后随即进入蠕变阶段,深部粉砂岩的侧向蠕变发展较轴向蠕变快;在蠕变过程中存在一个应力阈值,其中轴向蠕变的应力阈值比侧向蠕变的大。随轴向分级荷载的提高,岩石的瞬时弹性模量呈先增加后减小的变化趋势,瞬时泊松比呈上凹型增长,轴向蠕变应变先减小后增大,侧向蠕变应变呈前期增长平缓的上凹型增长;根据试验过程中的等时应力应变曲线的变化趋势,可以看出深部粉砂岩蠕变过程具有非线性特征,且侧向蠕变较轴向蠕变更明显。

To investigate the creep characteristic of deep hard rock,the uniaxial compressive creep tests of deep siltstone were carried out under step loading condition.The test results show that creep stage is occurred after instantaneous axial strain and lateral strain caused by step loading,and the deformation rate of lateral creep is faster than that of axial creep under step loading condition.There is a stress threshold for deep siltstone during the process of creep test,and the stress threshold of axial creep is higher than that of lateral creep.With the increase of axial loading pressure,the instantaneous elastic modulus firstly increases and then decreases,and the instantaneous Poisson’s ratio increases in the shape of concave.The axial creep strain firstly decreases and then increases,and the lateral creep strain increases in the shape of concave with a slow growth at the early stage.Nonlinear characteristics of deep siltstone are also observed by analyzing the isochronous stress-strain curve,and the nonlinear characteristic of lateral creep is more obvious than that of axial creep.