Purpose of soil classification

Soil classification groups soils of similar engineering behaviour into the same class, using simple index properties (grain size and plasticity).

Purposes and importance

1. Common language: engineers share a standard name and symbol for a soil (e.g. SC, CH), so reports are understood by everyone.
2. Prediction of behaviour: from the group, the probable strength, compressibility, permeability, compaction and swelling can be estimated.
3. Preliminary design: gives approximate design values (bearing capacity, subgrade suitability, frost susceptibility) before costly tests are done.
4. Selection of construction material: helps to select borrow soil for embankments, dam cores, and road subgrades.
5. Site investigation planning: helps decide what tests are needed.
6. Use of past experience: data from similar soils elsewhere can be applied.
7. Economy: avoids costly lab tests for small or simple projects.
8. Correlation: index properties correlate with engineering properties (e.g. $w_L$ with compression index).