Brief information on Standard Penetration Test
SPT alias The Standard Penetration Test is considered as most recognized and inexpensive test that is conducted to find out the surface information on both land and offshore. This test is most suitable for detecting the bearing strength of soil.
The following equipments 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.
7. Extension rods.
Theory of Standard Penetration Test: The number or blows are necessary for 12 inches penetration resistance of the soil. It is usually defined as the ‘N’ value and calculated in blows/unit penetration.
The Standard penetration test ( SPT ) is very suitable for obtaining the bearing strength of soil directly at a specific depth. The stability of clayey soils can is calculated frequently from this test.
If a borehole is expanded to a prearranged depth, the drill tools are eliminated, and the sampler (split spoon) is deflated to the bottom of the borehole.
The sampler is pushed into the soil, by punching to the top of the drill rod with hammer. The standard weight of the hammer is 140 lbs.(62.3 N). The number of blows necessary for spoon infiltration of three “6” inches (15 cm) intervals is listed.
The number of blows necessary for the last two intervals is included to provide the standard penetration number at that depth.
Standard Penetration Test Method:
1. Construct the tripod over the test hole and set up the unit.
2. Ensure the spoon is lied on the bottom of the hole.
3. Push the spoon with blows from the hammer falling 75 cm (30 inches), unless either 45 cm (18 inches) are infiltred or 100 blows are employed.
4. Record the number of blows necessary to perform each 15 cm (6 inches) of penetration. The first 6 inches is treated as seating drive.
5. The number of blows necessary for the second and third 15 cm (6 inches) of drive added is taken as the penetration resistance value (N) of the soil.
To get more detail about the test, go through the following construction article. civilguides.com
Video Source: Milad Fatehnia