INFLUENCE OF THE SCALE EFFECT ON THE MECHANICAL PARAMETERS OF COARSE-GRAINED SOILS

The mechanical parameters of coarse-grained soils are often obtained via indoor or field tests. In these tests, it is necessary to reduce the particle size of the original graded soils due to the size limitation of the testing apparatus. Therefore, several scale methods (e.g., the equivalent substitute method and parallel gradation method) have been proposed to reduce the size of the original graded soils to the proper testing size. However, the mechanical parameters will be different if different scale methods are adopted, a phenomenon that has been termed the “scale effect”. In this research, a group of large-scale oedometer tests were conducted with specimens that were downsized using different scale methods. The results show that (1) when adopting the same scale methods, the compression modulus increases with the increase in the nominal maximum particle size. (2) For the same nominal maximum particle size, samples that are downsized using the equivalent substitute method have a higher compression modulus and degree of particle breakage than those adopting the parallel gradation method. (3) Then Duncan-Chang E-B model parameters were back calculated from oedometer tests using an immune genetic algorithm (IGA). These mechanical parameters were also used in a three-dimensional (3D) finite element method analysis of the Pankou Rock-fill Dam. The manner in which the scale method influences rock-fill dam deformation is also discussed.