落锥法确定粉土液限和塑限的试验研究

针对部分细粒土进行了室内落锥法确定液限和塑限的试验研究，试验结果表明：对于一些细粒土在双对数坐标上圆锥下沉深度与含水率之间的关系并非线性关系，无法依据线性关系确定液、塑限；采用规程建议的3个含水率范围有时根本无法获得有效试验数据，采用规程建议的3个含水率范围确定得到粉土的液、塑限试验结果的可靠性有待商榷；采用直线段试验数据确定的液、塑限进行分类可能出现相互矛盾甚至错误的结果。进一步试验结果表明：对于黏粒含量高于13 %的粉土，由于其抗剪强度以凝聚分量为主，落锥法适用，所测塑性指数能够反映其可塑性；对于部分黏粒含量低于13 %的粉土及外观接近粉土的粉砂，由于其抗剪强度以颗粒间摩擦分量为主，落锥法不再适用，所测塑性指数不能反映其可塑性。

Experimental research on fall cone test to determine liquid limit and plastic limit of silts

A series of fall cone tests are performed to determine the liquid limits and the plastic limits of fine grained soil. The result shows that the log-log relationships between penetration depth of fall cone and water content of some fine grained soil are clearly nonlinear; and the liquid limits and the plastic limits can not be obtained according to the linear relation. Effective test data can not be measured within the three ranges of water contents proposed by the present standards. The dependability is necessary to discuss about the liquid-plastic limit test results obtained from three ranges. It is possible that the contradictory and wrong classification results exist by using the liquid limits and the plastic limits obtained from the test data with straight line. The further test results show that the fall cone test is suitable for the silts over 13 % clay particles content since the shear strength is mainly controlled by cohesion; and the plasticity is available from the plasticity indexes. On the contrary, the fall cone test is not suitable for the other silts and the silty sands which are similar to silts, because the shear strength is mainly controlled by particle friction. At last, some opinions about the fine grained soil classification are given.