Soil Classification

Soil explorations, that are to be carried out to the required extent and then to be appropriately evaluated, form the basis for the structural calculations of already existing, newly to be laid, or to be rehabilitated drains, sewers and associated structures by means of the open cut or trenchless method of construction.

For these applications, [ASTM D2487-06] classifies the types of soils as follows:

• Category I: Clean, course grained soils: SW, SP, GW, GP or any soil beginning with one of those symbols with 12% or less passing a #200 sieve

• Category II: Course grained soils with fines: GM, GC, SM, SC or any soil beginning with one of these symbols, containing more than 12% passing a #200 sieve; Sandy or gravelly fine– grained soils: CL, ML, (or CL-ML, CL/ML, ML/CL) with 30% or more retained on a #200 sieve

• Category III: Fine-grained soils: CL, ML, (or CL-ML, CL/ML, ML/CL) with less than 30% retained on a #200 sieve

• Category IV: MH, CH, OL, OH, PT

For additional information, please see Soil classifications for soil designations (equivalent USCS and AASHTO) and Soil classification chart per [ASTM D2487-06].