砂岩三轴卸荷力学特性试验研究

基于三轴卸荷破坏试验,分析研究砂岩在卸荷应力状态下的应力-应变及破坏特征。试验结果表明:岩体卸荷破坏时脆性特征非常明显,相比于加载破坏,卸荷破坏更加突然和剧烈,岩体破碎程度更高;卸荷过程中轴向变形随围压降低不断增加,在开始卸荷阶段增加较慢,当卸荷量达到一定值后,变形突然增大,很小的卸荷量就会引起较大的变形。根据卸荷过程中岩体应力-应变曲线变化特征,将卸荷量作为重要参量,假定岩体在卸荷损伤屈服阶段符合Griffith屈服准则,接近极限破坏强度时符合Hoek-Brown屈服准则,认为卸荷造成岩体屈服发生塑性变形后,岩体卸荷条件下的屈服函数随卸荷量在Griffith准则和Hoek-Brown准则间呈线性变化,推导考虑卸荷应力状态的弹脆塑性力学模型。

EXPERIMENTAL STUDY OF SANDSTONE MECHANICAL PROPERTIES BY UNLOADING TRIAXIAL TESTS

Based on the results of triaxial unloading tests，the stress-strain characteristics and failure characteristics of sandstone have been discussed. The results show that the brittle characteristic of sandstone failure under unloading conditions is obvious. Compared to loading failure，unloading failure is more sudden and severe with a higher degree of rock fragmentation. Axial deformation increases continuously with decreasing confining pressure during unloading；and it increases slowly at the beginning of unloading. When the unloading reaches a certain value，deformation suddenly increases；a little change in confining pressure can cause large unloading deformation. Considering unloading degree as an important parameter，an elastic-brittle-plastic mechanical model has been established according to the characteristics of rock mass stress-strain curves under unloading conditions，which assuming that rock mass conform to Griffith criterion in unloading damage segment and Hoek-Brown criterion in unloading failure segment，unloading yield function varies linearly between Griffith and Hoek-Brown criteria.