锯齿状结构面剪切蠕变、松弛及长期强度研究

Study on shear creep, relaxation and long term strength of serrate structure surface

摘要:

为对结构面的蠕变、松弛和长期强度进行综合分析，用水泥砂浆浇筑成不同角度的结构面试样，采用相同的分级加载方法，在岩石双轴流变试验机上对规则齿形结构面进行剪切蠕变试验和松弛试验.首先分析了蠕变特性与松弛特性的异同及蠕变和松弛过程中剪应力-位移曲线的差异，其次基于蠕变速率及蠕变与松弛关系，推导能够描述应力松弛的经验方程，最后分别基于蠕变试验和松弛试验确定结构面的长期强度，并对长期强度进行对比分析.研究结果表明：蠕变曲线与松弛曲线形态相似，变化趋势相反；蠕变变形量和应力松弛量都随结构面爬坡角的增大而增大；蠕变过程和松弛过程的剪应力-位移曲线显示两者的应力-应变路径不同，表明蠕变和松弛过程中能量变化不同，且由于不可逆功的存在，不能简单认为蠕变和松弛是等价的；本文提出的应力松弛方程，能够较好地描述松弛过程，但蠕变方程和松弛方程的拟合参数值相差约1个数量级；基于相同的机理，根据蠕变试验和松弛试验确定的结构面长期强度不同，相差约为9%，而且长期强度值与蠕变过程和松弛过程中剪应力-位移曲线的屈服强度比较接近.

Abstract:

To comprehensively analyze the creep, relaxation, long-term strength of serrate structure surface, the creep and stress relaxation tests of dentate discontinuity poured by cement mortar were carried out using biaxial creep machine under step load. Firstly, the similarities and differences between creep and relaxation were analyzed, and the differences of shear stress-displacement curves in creep process and relaxation process were compared. Secondly, a new stress relaxation model was presented based on the creep rate equation and the relations between creep and relaxation. Finally, the long term strength was determined separately by creep test and relaxation test, and contrastive analyses were made. The results show that the creep curve has similar shape with stress relaxation curve, but the trend of the creep curve is opposite to that of the stress relaxation curve. The creep deformation and stress relaxation amount increase with the increase of slope angles. The shear stress-displacement curve during creep test process and relaxation test process reveal the stress-strain path of creep differently from relaxation, which indicates the energy change in creep test different from relaxation test, so it cannot be simply considered to be equivalent between creep and relaxation due to the irreversibility of work. Though the stress relaxation model can fits the experimental data better, the differences among the orders of magnitude of the the parameter in creep equation and relaxation equation are 1 series. Based on the same mechanism, the long term strength of creep test is similar to that of relaxation test, in which the difference rate is about 9%. The long term strength is very close to yield strength in the shear stress-displacement curve of creep test and relaxation test.