季节性冻融环境是加剧寒区岸坡开挖卸荷岩体力学强度衰减的关键因素之一,为研究冻融作用下某岸坡开挖卸荷岩体的时效力学特性,开展了以砂岩为对象的三轴卸荷试验,进行了模拟冻结强度的冻融循环试验,以遭受冻融作用的卸荷试样为对象,采用分级增量加载方式实施了三轴蠕变试验。结果表明：①与常规试样相比,卸荷试样的总体变形明显增加,且侧向相比轴向更容易产生蠕变行为。围压量级决定着卸荷试样蠕变变形的量级,且影响着蠕变速率的变化规律;②冻融作用加剧了卸荷试样的蠕变行为,冻结周期越长,蠕变应变占比越大且蠕变速率明显增大;③遭受冻融作用的卸荷试样,其蠕变破坏形态主要表现为剪切破坏,蠕变过程加剧了试样张拉型裂纹的衍生;卸荷试样的围压越高,蠕变破坏时的塑性特征愈加明显且脆性特征减弱;④冻融作用显著削减了卸荷试样的长期强度、约为瞬时强度的55%,长期强度伴随冻结周期增加存在显著的衰减特征。所得研究成果可为寒区岩坡开挖卸荷岩体长期稳定性评价提供理论参考。
Seasonal freeze-thaw conditions are one of the key factors exacerbating the mechanical strength decay of excavated and unloaded rock on reservoir banks in cold regions. In order to study the effective mechanical properties of an excavated unloaded rock mass on a bank slope under freeze-thaw action, triaxial unloading tests were carried out on sandstone, freeze-thaw cycling tests were carried out to simulate freezing strength, and triaxial creep tests were carried out on unloaded specimens subjected to freeze-thaw action using graded incremental loading. The results show that the overall deformation of unloaded specimens is significantly higher than that of conventional specimens, and creep is more likely to occur in the lateral direction than in the axial direction; the level of envelope pressure determines the level of creep deformation of unloaded specimens and affects the variation pattern of creep rate; the freezing and thawing exacerbate the creep behavior of unloaded specimens, and the longer the freezing period, the greater the percentage of creep strain and the creep rate increases significantly; the unloaded specimens subjected to freezing and thawing are mainly characterized by shear damage, and the creep process exacerbates the derivation of tensile cracks. The creep damage is mainly in the form of shear damage, and the creep process intensifies the derivation of tensile cracks in the specimens; the higher the peritectic pressure of the unloaded specimens, the more plastic and less brittle the creep damage is. The freeze-thaw action significantly reduce the long-term strength of the unloaded specimens, which is about 55% of the instantaneous strength, and the long-term strength decreases significantly with the increase of freeze-thaw cycle and has a lower threshold value. The results of the research can provide a theoretical reference for the evaluation of the long-term stability of unloaded rock masses in excavations on cold slopes.
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