不同卸荷水平下饱和红砂岩三轴压缩破坏及能量演化特征

Characteristics of triaxial compression damage and energy evolution of saturated red sandstone under different unloading levels

为保证水下红砂岩地层隧道的安全施工,避免开挖区突水、失稳等工程事故的发生。以赣州蓉江四路过江隧道工程为依托,对饱和状态下的泥质红砂围岩开展初始卸荷水平为60%、70%、80%和100%(无卸荷)的三轴压缩对比试验,分析不同初始卸荷水平下三轴压缩力学特性变化规律,并结合扫描电镜,对试验后岩样的宏细观破坏特征进行对比分析。基于能量耗散原理,对不同初始卸荷水平下饱和泥质红砂岩试样的能量关系进行拟合,揭示卸荷过程中的破坏特征与能量演化之间的规律。研究结果表明:无卸荷三轴压缩破坏时的峰值偏应力远高于初始卸荷水平为60%、70%、80%时的峰值偏应力,随着初始卸荷水平的提高,饱和泥质红砂岩的峰值偏应力在增加,偏应力增加值在减少,环向变形减小,卸荷所导致的岩样扩容时间会更短,岩样内部的裂隙及黏结颗粒碎屑和表面的破裂纹路增多并发生贯通,且受张拉破坏越明显。在卸荷条件下,三轴压缩达到屈服阶段后,岩样裂隙快速发展,弹性应变能增加缓慢,耗散能急剧增加,破坏阶段时,岩样内部存储的弹性应变能达到存储极限并瞬间释放,产生更多的裂隙。随着初始卸荷水平的提高,峰值偏应力对应的总应变能、弹性应变能及耗散能均呈现先减小后增大的趋势。研究结果可为红砂岩分布地区的水下隧道开挖及建设提供一定的理论参考。

To ensure the safe construction of tunnels in underwater red sandstone strata,and to avoid the occurrence of engineering accidents such as water surge and destabilization in the excavation area.Based on the Ganzhou Rongjiang 4th Road Crossing Tunnel Project,triaxial compression tests with initial unloading levels of 60%,70%,80%,and 100%(no unloading)were carried out on the saturated muddy red sand perimeter rock to analyze the changing rules of the mechanical properties of triaxial compression under different initial unloading levels.Combined with scanning electron microscopy,the macroscopic damage characteristics of the rock samples were comparatively analyzed after the tests.Based on the principle of energy dissipation,the energy relationship of saturated muddy red sandstone specimens under different initial unloading levels was fitted to reveal the law between the damage characteristics and energy evolution during the unloading process.The results are shown as follows.The peak deviatoric stress in unloaded triaxial compression damage is much higher than that under the initial unloading level of 60%,70%,and 80%.With the increase of initial unloading level,the peak deviatoric stress of saturated muddy red sandstone is increasing,the value of the increase in the deviatoric stress and the circumferential deformation is decreasing.The time of expansion of the rock samples due to unloading is much shorter.The fissures and bonded particles of the debris and the fracture lines on the surface of the rock samples are increased and penetration occurs and the more pronounced the damage is caused by tensions.Under the unloading condition,the cracks of the rock samples develop rapidly and the elastic strain energy increases slowly after the triaxial compression reaches the yield strength.The dissipated energy increases sharply,and the elastic strain energy stored inside the rock samples reaches the storage limit during the destructive stage and releases instantaneously leading to the generation of more cracks.As the initial unloading level increases,the total strain energy,elastic strain energy and dissipation energy corresponding to the peak deviatoric stress show a decreasing and then increasing trend.The research results can provide some theoretical references for the excavation and construction of underwater tunnels in the red sandstone distribution area.