1. Field Methods of Soil Classification
ACPA 2017 Pipe School
Norman Dennis
January 5, 2017

2. Installation Type and Bedding Categories

3. Soil Bedding Categories

4. Unified Soil Classification System (USCS)
Based on grain size distribution and plasticity.
Hierarchical System
Good material at the top
Poor material at the bottom
Need: Sieve Analysis
Liquid Limit (LL)
Plastic Limit (PL)
Hydrometer Analysis
Plasticity Index (PI) = LL-PL

5. USCS – Coarse Grained Soil
Category I - Well and Poorly Graded Gravels and Sands
≤ 5% Passing #200 sieve
(practically ≤ 12%)
Category II
>12% Passing #200 sieve
< 50% Passing #200 sieve
Clay must be low plasticity (CL)
Note: #200 sieve particle size is mm or ~ inches

6. USCS – Fine Grained Soil
≥ 50% Passes # 200 Sieve
Category II
Category III
Also GC and SC with highly plastic clay fines

7. ASSHTO Soil Classification System –Coarse Grained
Category I
Category II

8. ASSHTO Soil Classification System – Fine Grained
Category II
Category III

9. Field Particle Size Analysis
Place about 3 inches of soil in a 100 ml graduate cylinder
Fill with water to 100 ml mark.
Mark side of cylinder with pencil at top of soil.
Shake well to get all soil in suspension
Set graduate cylinder down and wait 30 seconds.
Mark top of soil (Gravel and Sand fraction)
Wait 50 minutes (Silt Fraction)
Wait 24 hours (Clay fraction)

10. Smear Test (degree of plasticity)
Add water to a pinch of soil to create a soft putty like paste.
Smear the soil between the thumb and forefinger.
Alternatively drag a thumbnail across the soil pat.
Rough or dull texture of the smear indicates low plasticity
Smooth waxy like texture indicates high plasticity

11. Dilatancy Test (CH) (MH or CL) (ML)
Mix soil and water to create a ball about inches in diameter of soft putty-like consistency.
Hold ball in palm of one hand squeeze the ball then hit the open palm sharply with the other hand repeatedly. Squeeze the ball again.
(CH)
(MH or CL)
(ML)

12. Thread Test
Work the water out of the dilatancy ball until it starts to crack or break apart when molded.
Roll out a soil worm to the smallest possible diameter before disintegration.
Low plasticity threads will be 1/8 inch or larger when breaking up.
High plasticity threads may be rolled to 1/32 of an inch or smaller.

13. Dry Strength Test
Add water to a pinch of soil to create a ball about ¼- ½ inch in diameter.
Allow ball to dry (can use a heat source (< 140 F, 45 C)
Using the Thumb press the ball against a hard surface.

14. Soil Plasticity

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