Method Of Standard Penetration Test

The SPT test alias Standard Penetration Test is mostly recognized among construction professionals that is carried out to find out the surface information for both land and offshore.

The purpose of this soil penetration test for soil testing is to determine the bearing capacity of soil directly at a specific depth.

The following tools are used for standard penetration test :-

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 plays an important role for 12 inches penetration resistance of the soil. It is normally defined as the ‘N’ value and calculated in blows/unit penetration. This test can also calculate to find out the uniformity of clayey soils.

After expanding a borehole to a certain depth, the drill tools are detached, and the sampler (split spoon) is dropped to the bottom of the borehole.

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

The number of blows necessary for the last two intervals are taken into consideration to provide the standard penetration number at that depth.

Standard Penetration Test Method:

Also Read: How to determine the bearing strength of shallow foundation

1. Set up the tripod over the test hole and compile the unit.

2. Set the spoon in much a manner that it can stand on the bottom of the hole.

3. Enter the spoon with blows from the hammer falling 75 cm (30 inches), unless either 45 cm (18 inches) are inserted or 100 blows are used.

4. Record the number of blows necessary to impact each 15 cm (6 inches) of penetration. The first 6 inches is taken as seating drive.

5. The number of blows necessary for the second and third 15 cm (6 inches) of drive added is recorded like the penetration resistance value N of the soil.

To get more clear ideas, go through the following video :-

Video Source: Milad Fatehnia