Geotechnical Engineering
Soil Classification Helper
Screen a preliminary USCS soil group using gradation percentages and Atterberg limits.
Parameter sketch
Gradation and plasticity screening
Labels update with the current input values so the formula symbols stay tied to the geometry.
gravel: 20%sand: 45%fines: 35%LL: 42PI: 18
Result
Preliminary USCS group: SC
Coarse fraction
65
Fines fraction
35
A-line PI
16.1
USCS symbol
SC
Step-by-step calculation
- Coarse fraction = gravel + sand = 65%.
- A-line PI = 0.73 x (42 - 20) = 16.1.
- Compare measured PI 18 with the A-line and fines percentage.
What this means
Use this helper as a screening aid only. Full USCS classification requires gradation curve details and lab procedures.
Formula Used
A-line PI = 0.73(LL - 20)
Step-by-Step Example
A soil with 20% gravel, 45% sand, 35% fines, LL=42, and PI=18 screens as SC.
Engineering Notes
Check units, assumptions, boundary conditions, groundwater, drainage, and whether the simplified method is appropriate before using a result in any project decision.
FAQ
Is this a lab classification?
No. It is a screening helper and does not replace ASTM or project lab procedures.