Bimodal Features for Widely-Graded Soils

The microporosity structure of coarse granular soils with various coarse/fines contents has been introduced in Chap. 3. The skeletons of five types of compacted and saturated specimens change from clay aggregates to coarse particles gradually. The soils with coarse contents greater than 70% have a coarse-controlled microstructure and the soils with coarse contents lower than 70% have a fines-controlled microstructure. The coarse-controlled soils, such as GW-GM with sand and SM with gravel, dual-porosity structure are formed during the soil compaction and show limit changes after wetting and drying. As presented in Chap. 5, Figs. 5.6, 5.7, and 5.32, the SWCCs and SHCFs for colluvial soils with high coarse fractions show a bimodal feature with two air entry values and is essentially relates to a dual-porosity structure.