|Standard Penetration Tests
The Standard Penetration Tests aims to determine the SPT N value, which gives an indication of the soil stiffness and can be empirically related to many engineering properties.
The test is conducted inside a borehole. A 'split spoon' sampler is attached to the bottom of a core barrel and lowered into position at the bottom of the borehole. The sampler is driven into the ground by a drop hammer weighing 68 kg falling through a height of 76 cm. The number of hammer blows is counted. The number required to drive the sampler three successive 150mm increments is recorded. The first increment (0-150mm) is not included in the N value as it is assumed that the top of the test area has been disturbed by the drilling process. The SPT N is the number of blows required to achieve penetration from 150-450mm.
The hammer weight, drop height, spoon diameter, rope diameter etc. are standard dimensions.
After the test, the sample remaining inside the split spoon is preserved in an airtight container for inspection and description.