板裂化模型试样失稳破坏及其裂隙扩展特征的试验研究

Experimental study of instability destruction and crack propagation characteristics of slab failure model specimen

锦屏二级水电站深埋隧洞大量岩爆案例表明板裂化围岩的失稳破坏与岩爆之间具有很强的相关性。采用高强石膏配制满足板裂化围岩结构特征的硬脆性模型试样,通过一侧约束条件下的单轴压缩试验研究板裂化模型试样的失稳破坏过程、强度与变形特性及其裂纹扩展特征。研究表明,(1)板裂化模型试样失稳破坏过程表现出应变型岩爆的特征,其典型的破坏过程为预制裂隙尖端张拉裂纹的萌生与扩展-试样劈裂成板-岩板屈曲变形-岩板压折、岩片弹射;(2)与完整试样相比,含1条、2条、3条预制裂隙模型试样的峰值强度、弹性模量均呈现稳定下降的趋势,而峰值轴向应变则是先减小后增大;(3)试样预制裂隙尖端张拉裂纹的产生会造成:相邻预制裂隙尖端横向应变值的突变、试样侧向变形量的突增以及侧向变形速率的显著增大;(4)临空面附近的预制裂隙,其尖端产生的张拉裂纹在很短的时间内便会失稳扩展,并造成试样的失稳破坏。最后,分析试样变形破坏过程中的声发射特性。研究结果对于揭示深埋硬岩隧洞板裂化围岩的失稳破坏规律、岩爆的发生机制具有重要意义。

A large number of rockburst cases happened in deep tunnels of JinpingⅡhydropower station revealed that the slab failure of surrounding rock has a strong relationship with rockburst. Model specimens that meet the architectural feature of slab failure are made by using high-strength gypsum. Instability destruction process, strength and deformation characteristics, crack propagation signature of model specimens are researched under the condition of one lateral side restraint uniaxial loading mode. The results show that(1) the instability destruction process of the slab model specimens shows the characteristics of strain rockburst. A typical failure process can be described as follows: initiation and propagation of extension crack from the tip of pre-existing fissure, splitting into slabs, flexure deformation of slabs, buckling of slabs and ejection of slices.(2) The peak strength, elastic modulus of model specimens containing one, two and three pre-existing fissures show a steady decline law, but the peak axial strain decreases and then increases.(3) The emergence of extension crack will result in: a sudden change of the lateral strain near the tip of adjacent fissures and a significant increase in the amount and the rate of lateral deformation of the specimens.(4) Due to the affect of the free surface, extension crack will enter into unstable propagation stage in a short time after its initiation from the tip of pre-existing fissure that near the free surface of specimens and this will lead to the overall instability of the model specimen. At last, acoustic emission characteristics of specimen in the overall stage of compression deformation are analyzed. The research results are of important significance for the reveal of the instability destruction law of slabbing surrounding rock and the rockburst formation mechanism of deep tunnel in hard rock.