How many groups of soils come under the Indian standard soil classification system?
The Indian Standard Soil Classification System (ISCS), first developed in 1959, was revised in 1970. The fine-grained soils have been subdivided into three groups (Low, Medium, and High Plasticity).
In all, there are 18 groups of soils: 8 groups of coarse-grained, 9 groups of fine-grained, and 1 group of peat.
Each of the above sub-divisions is further sub-divided into four groups depending upon grading and inclusion of other materials:
GW = Well graded, clean
GC = Well graded with an excellent clay binder
GP = Poorly graded, fairly clean
GM = Containing fine materials not covered in other groups.
Examples are-Well graded gravels, poorly graded gravels silty gravels, Clayey gravels, SW(Well graded sand), SP(poor graded sand), SM and SC and Inorganic Silts, Peat, and other highly organic soils.