针对以粗粒土为代表的软弱层带在水电、铁路等交通领域对边坡及洞室围岩稳定性的控制,结合某水电工程坝区,分别对岩块岩屑型和岩屑夹泥型两种软弱夹层,在考虑一定围压作用下进行了天然含水状态和饱水状态的现场直剪试验.结果显示,剪应力-剪切位移曲线饱水前、后均呈现出微弱的峰值,整体均表现为塑性破坏特征,饱水前、后发生屈服前的剪切位移分别为5 mm和10 mm以内.在强度参数上,两类夹层饱水前、后峰值强度内摩擦系数降低幅度一般在8%～10%,残余强度一般降低5%以内.表明以粗粒土为代表的软弱层带由于细粒(＜0.075 mm)物质少,细粒起不到包裹粗颗粒而作为润滑作用,同时因围压效应,饱水对其强度参数的影响有限,因此不同含水状态对该类软弱层带内摩擦角和内聚力均无显著影响,其强度参数主要还是取决于夹层本身的颗粒成分.%Due to the control action of non-clay weak interbed composed by coarse-grained soil to the stability of slope and surrounding rock masses in hydropower, railway and other transportation field, combined with the dam area of a hydropower projects, considering the effect of confining pressure, in-situ shear test on two types of weak interbed under natural and saturated state is carried out. The results showed that a faint peak appeared in the shear strength versus. shear displacement curve before and after saturation, the plastic deformation failure characteristics were performed in the overall curve, and the shear displacement under yielding were less than 5 mm before saturation and less than 10 mm after saturation. For the strength parameters, internal friction coefficient of the peak strength before and after saturation of the two types of weak interbed was decreased generally 8％ to 10％, the residual strength was generally reduced no more than 5％. According to the test, it can be found that because the finegrained material ( ＜0.075 mm) accounted for low proportion in the non-clay weak interbed composed by coarsegrained soil, the fine-grained material cannot wrap the coarse-grained to form lubricant. At the same time due to confining pressure effect, saturation state had little influence on the strength parameters. Therefore, the test represented that different saturated state had no significant effect on the internal friction and the cohesion in the no-clay weak interbed, and the strength parameters of the weak interbed were mainly depended on the particles composition of itself.
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