GRADATION CHARACTERISTICS AND DISCRIMINATION METHODS OF CRUSHED GRAVEL WITH FINE GRAIN CONTENT(Pc35%) AND SEEPAGE DEFORMATION OF PIPING

Fine grain content criterion is a main discriminant method for the seepage deformation type of cohesionless coarse grained soil. However the seepage deformation type(piping) of crushed gravel(Pc35%) does not conform to the fine grain content criterion. According to the statistical analysis on seepage deformation testing results with 310 specimens from 46 projects(in which, the number of samples(Pc35%) is 35),the grain grading curves have such an unique characteristic that the slope of both ends of the gradation curve is steeper, and the slope of the middle segment is slow, so up to 87.5% of sampling particles are poorly-graded. Further analysis shows that the ratios of D15/d8 are more than 5,which means that the test results of seepage deformation are consistent with the filter criteria. Therefore the filter criteria are taken as a discriminant method for this kind of soil, and as a beneficial supplement for the fine grain content discrimination method as well.