Split Spoon
Sampling 

A split spoon sampler is a steel cylindrical tube that can be separated lengthwise (split) into two halves. This design allows easy access to the soil sample inside after retrieval.

Typical Dimensions

• Outer diameter: ~2 inches (51 mm)
• Length: ~18 to 30 inches
• Wall thickness: ~1/8 to 1/4 inch

How Split Spoon Sampling Works (in SPT context)

1. Drill a Borehole
   • A hollow stem auger or mud rotary rig advances the borehole to the desired depth.
2. Lower the Sampler
   • The split spoon sampler is attached to drill rods and lowered to the bottom of the borehole.
3. Drive the Sampler with a Hammer
   • A 140 lb (63.5 kg) hammer is dropped from a height of 30 inches (76 cm) to drive the sampler into the soil.
   • The sampler is driven 18 inches (45 cm) total, and the number of hammer blows for each 6-inch (15 cm) increment is recorded.
4. Retrieve and Open the Sampler
   • The sampler is pulled up, opened, and the disturbed soil sample is removed for logging and lab testing.

What Is the SPT “N-value”?

The SPT N-value is the number of hammer blows required to drive the split spoon sampler the last 12 inches (30 cm) into the soil.
It’s a key measure of soil resistance or density:

• Loose sand: 0–10 blows
• Medium sand: 10–30 blows
• Dense sand: 30–50+ blows
• Very dense or refusal: >50 blows

Advantages

• Widely standardized (ASTM D1586)
• Quick and relatively inexpensive
• Provides both a sample and in-situ soil resistance

Limitations

• Disturbed sample – not suitable for detailed structure or permeability analysis
• Not ideal in gravelly or very soft soils (low recovery or sampler refusal)
• Results can be influenced by equipment type, operator, and borehole conditions