top of page

    SPT Soil Drilling

SPT  (Standard Penetration Test) drilling and is intended for trial drilling and soil density testing.


The drilling is carried out using a special drill consisting of a pipe and a hammer and a procedure of drilling and punching the insertion of the sample pipe, which allows conclusions to be drawn regarding the density of the sampled soil.


SPT drilling

The standard insertion drilling process, SPT drilling, is based on the use of a thick-walled sampling pipe, with an external diameter of 50.8 mm and an internal diameter of 35 mm, and a length of around 650 mm.

This pipe is driven into the ground, at the bottom of the borehole, by blows from a 63.5 kg hammer with a swing of 760 mm (30 inches). The sampling pipe penetrates 150 mm into the ground and then the number of blows required for the pipe per 150 mm (6 inches) up to a depth of 450 mm (18 inches) is recorded. The sum of the number of blows required to penetrate the second and third 6 inches of penetration, called the “standard penetration resistance” or “N-value.” In cases where 50 blows are not enough to advance it 150 mm (6 inches) apart, the penetration is recorded after 50 blows.

The blow count provides an indication of soil density, and is used in many empirical geotechnical engineering formulas.

The SPT drilling procedure is recognized in international standards such as ISO 22476-3, ASTM D1586 and also the Australian Standard AS 1289.6.3.1.


When and how much?

The need for soil drilling in general and SPT drilling in particular, will be determined by the soil consultant based on the analysis of the needs and designations of the area. Among the considerations for choosing the SPT drilling method:

1. Accessibility of the sampling site (restricted access, electricity/water infrastructure, closed building, etc.).

2. The depth and diameter of the drilling, according to the planned constructionNat.

3. The type of land.

4. Designation of the tear and building plan.

Of course, the more drillings are carried out, the richer information is obtained and which enables a more accurate and reliable decision to be made. However, the land consultant together with the constructor know how to optimize the layout of the drillings according to professional considerations and such as those listed above.


Evaluation of standard insertion drilling products

To enable an initial evaluation of the products of the drilling process using the SPT method, the following table is accepted:

bottom of page