Standard Penetration Test Procedure

The Standard Penetration Test (SPT) is most popular and economical test to determine the surface information, both on land and offshore. This test is widely used to obtain the bearing capacity of soil.

Standard Penetration Test Tools.

1. Drilling Rig.

2. Split spoon (tube).

3. Drop hammer 65 kg (140 lbs ).

4. Driving head (anvil).

5. Guiding rod.

6. Tripod.

7. Extension rods.

Standard Penetration Test Theory.

The number or blows required for 12 inches penetration resistance of the soil. It is generally referred as the ‘N’ value and measured in blows/unit penetration.

The Standard penetration test ( SPT ) is widely used to get the bearing capacity of soil directly at a certain depth. The consistency of clayey soils can often be estimated from this test.

When a borehole is extended to a predetermined depth, the drill tools are removed, and the sampler (split spoon) is lowered to the bottom of the borehole.

The sampler is driven into the soil, by hammer blows to the top of the drill rod. The standard weight of the hammer is 140 lbs.(62.3 N) the number of blows required for spoon penetration of three “6” inches (15 cm) intervals is recorded.

The number of blows required for the last two intervals are added to give the standard penetration number at that depth.