干湿状态对红层软岩脆延特性影响的试验研究

Experimental Research on Effects of Dry and Natural States on Brittle-Ductile Transition Property for Red-Bed Soft Rock

为研究含水状态对脆延转化特性的影响,针对工程性质特殊的胡麻岭隧道红层软岩展开了系列试验,探究了干燥与天然含水状态试样脆延性区的强度变形规律。首先对干湿组红层软岩分别进行不同围压下的常规三轴压缩试验,进一步引入脆性指标对岩样脆性程度进行定量表征,并基于Mohr-Coulomb强度准则以及考虑结构强度的初始屈服面模型对各特征应力进行了分析。在此基础上通过试验,从宏细观尺度上探究了红层软岩脆延转化机理。研究表明:岩样干燥后,峰值强度增加了93.39%~145.35%,残余强度增加了77.83%~133.72%,脆延转化压力增加近40%,峰值应变降低了24.13%~88.92%;延性区的干湿试样的黏聚力近似为脆性区的1.8倍,但内摩擦角均小于脆性区,为脆性区的50.4%~90.5%;同时发现延性区试样在施加围压时已经进入了弹塑性变形阶段,且脆延转化压力等于等向固结压力。该研究内容可进一步丰富红层软岩的工程特性,并为穿越红层软岩地下工程的开挖支护提供理论依据。

To understand the influence of rock water content on the brittle-ductile transition(BDT)property,a series of tests were carried out on Humaling red-bed soft rock with special engineering properties to explore the strength and deformation laws of dry and natural rock samples.The triaxial tests for the dry and natural red-bed soft rock were conducted,the brittleness index was then introduced to characterize the brittle degree of rock samples quantitatively.Following Mohr-Coulomb strength criterion and initial yield surface model considering structural strength,the characteristic stress was analyzed and the BDT mechanism was explored in macroscopic and microscopic scales.Compared to the natural sample,the results show that the peak strength of dry sample increases by 93.39%-145.35%,the residual strength increases by 77.83%-133.72%,the BDT pressure increases by nearly 40%,however,the peak strain decreases by 24.13%-88.92%.Furthermore,the cohesion of the samples in ductile zone is 1.8 times that in brittle zone,but the friction angle in ductile zone is only 50.4%-90.5%of the brittle zone.The samples in ductile zone enter the elastic-plastic deformation stage under isotropic compression,and the BDT pressure equals to the isotropic consolidation pressure.This approach can further enrich the engineering properties of red-bed soft rock,and provide theoretical basis for excavation and support of red-bed soft rock in underground engineering.