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土的分类体系、分类标准和分类试验方法是一个不可分割的统一体。卡氏塑性图中的液限是用卡氏仪(碟式仪)试验求得的,而我国现行分类试验用的是76克瓦氏锥。这样就不可避免地给使用塑性图带来一系列问题。卡氏塑性图既是分类方法,也是分类标准。因此,将原塑性图坐标换算为76克锥系统原则上是不可的,逻辑上也是欠缺的。本文论证了分类试验中76克锥液限法对卡式图的明显不合理性,并提出了改进途径。推荐锥角30°、重量100克和入土深度h_L=20毫米的锥式仪作液限测定。根据试验,塑限时特定的入土深度h_p随土的类别而异,提出了两种确定h_p的方法,这样就可用锥式仪对土的液限W_L和塑限W_p进行联合测定。
Soil classification systems, classification criteria and classification test methods are an inseparable unity. The liquid limit in the Cartesian plasticity chart was obtained by the Karl Fischer (disc instrument) test, and the current classification test in China uses a 76-kV cone. This inevitably brings a series of problems to the use of plastic maps. The Cartesian plasticity chart is both a classification method and a classification criterion. Therefore, the conversion of the original plastic map coordinates to the 76-gram cone system is in principle impossible and logically absent. This paper demonstrates the obvious irrationality of the 76-gram cone-liquid method in the classification test for the cassette diagram, and proposes an improved approach. A cone meter with a cone angle of 30°, a weight of 100 g, and a depth of penetration of h_L=20 mm is recommended for liquid limit determination. According to the experiment, the specific depth of soil h_p varies with the soil type during the plastic limit, and two methods for determining h_p are proposed. Thus, the cone liquid level limit W_L and the plastic limit W_p can be jointly determined by a cone type instrument.