小南海红层坝基以洪泛平原细粒沉积为主, 粉砂岩-黏土岩不等厚互层的岩性组合、构造作用产生岩层屈曲及一定的地下水环境为层间剪切带的形成提供了条件。基于颗粒流理论, 采用离散单元法软件PFC2D建立了软弱相间岩层层间剪切带试样的颗粒流模型, 对剪切带试样的破坏发展过程进行了数值模拟, 分析了剪切带内孔隙比变化、剪切裂隙发展的位置、宽度、角度及间距, 模拟结果与A.W. Skempton提出的黏土实验室滑动面发展破坏过程一致。对比了8组不同厚度及延伸长度的剪切带试样的PFC数值模拟试验, 结果表明剪切带厚度及上下所夹硬岩尺寸一定时, 试样长度越长, 裂隙与层面夹角越小、裂隙间距越大, 微裂隙越容易集中在剪切带左右两端;试样长度和上下所夹硬岩厚度相同时, 剪切带厚度越大, 裂隙间距越大, 但裂隙与层面的夹角相近。
Abstract
The depositional environment of the bedrock of Xiaonanhai Dam is dominated by floodplain sub-facies. The strata are mainly composed of siltstone and mudstone interbedded. Tectonic leads to the buckling of layers, and groundwater causes the softening and mudding of wear intercalation. Those are three essential factors for the formation of intercalated shear zone in the alternatively distributed soft and hard rock layers. The macro-properties of shear zone can be simulated in mesomechanical level by particle flow code (PFC). On the basis of particle flow theory, PFC2D models of shear zone were established to study its shear failure process, in which different contact bond constitutive relations were introduced. The simulation test focused on the void ratio change, as well as the position, width, angle and spacing of the shear cracks. Results show that the shear failure process of the model is consistent with the development of slip surface in clay which was proposed by A.W. Skempton. Eight PFC2D models of shear zone samples with different thicknesses and lengths were compared, and the simulation results reveal that when the thickness of hard and soft rock is fixed, the longer sample leads to the gentler angle of the cracks and larger spacing between them. Meanwhile, micro-cracks are prone to be concentrated initially in both ends of the shear zone. Maintaining the length and the thickness of hard rock, the spacing of the cracks becomes larger with the increasing thickness of shear zone, but the angle remains unchanged.
关键词
红层 /
层间剪切带 /
颗粒流 /
细观力学 /
剪切破坏
Key words
red bed /
intercalated shear zone /
particle flow code /
mesomechanics /
shear failure
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基金
国家自然科学基金资助项目(41272308)
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