中低应变率加载下弱胶结软岩动力学特性

Dynamic characteristics of weakly consolidated soft rock under medium and low strain rate loading

我国西部侏罗系煤层上覆巨厚白垩系富水软岩,为了解此类软岩在冲击荷载作用下的力学本构关系及损伤演化规律,利用Hopkinson压杆装置对干燥、饱和红砂软岩进行中低应变率下的冲击试验,结果表明:红砂软岩峰值应力、峰值应变均表现出明显的应变率效应,其中峰值应力与应变率呈指数关系;相同应变率下,干燥红砂软岩的强度大于饱和状态,对冲击荷载表现出更强的抵抗能力,但饱和红砂软岩的宏观破坏强度大于干燥状态;低应变率加载下,干燥红砂软岩出现负损伤;结合微观机理分析,低应变率下,水对红砂软岩的弱化作用占据主导地位,随着应变率的增大,在惯性效应和水的Stefan效应共同作用下,饱和红砂软岩的动态强度得到强化;基于Z-W-T模型和应变等效原理,建立了服从Weibull分布的损伤本构方程,经验证能很好的反映红砂软岩的动态本构关系,具有一定的工程实际意义。

The Jurassic coal seam in western China covered with huge thick Cretaceous water-rich sandstone.To investigate the mechanical constitutive relation and damage evolution rule of this kind of soft rock under impact loading,the impact test on dry and saturated red sand soft rock with medium and low strain rate were carried out by using the Hopkinson pressure bar device.The results showed that the peak stress and peak strain of red sand soft rock showed an obvious strain rate effect.The relationship between peak stress and strain rate was exponential.Under the same strain rate,the strength of the dry red sand soft rock was bigger than that of the saturated,which showed the stronger resistance to impact load.But the failure strength of the saturated red sand soft rock was bigger than that of the dry state.Under low strain rate loading,the negative damage occurred by dry red sand soft rock.Combined with microscopic mechanism analysis,the weakening effect of water on red sand soft rock was dominant under low strain rate.With the increase of strain rate,the dynamic strength of saturated red sand soft rock was strengthened under the action of inertia effect and water Stefan effect.Based on Z-W-T model and strain equivalence principle,the damage constitutive equation obeying Weibull distribution was established,which could well reflect the dynamic constitutive relationship of red sand soft rock and had a certain practical engineering significance.