Standard Penetration Test

1. Scope of Standard Penetration Test (SPT)
1.1. Description of Standard Penetration Test (SPT)
This method describes the standard penetration test using the split-barrel sampler to obtain　the resistance of soil to penetration (N-value), using a 63.5 kg hammer falling 0.76m; and　to obtain representative samples for identification and laboratory tests.
The method is applicable to all soil types. It is most often used in granular materials but　also in other materials when simple in-place bearing strengths are required. It is also used　when samples cannot easily be recovered by other means.
2. Apparatus and Materials of Standard Penetration Test (SPT)
2.1. Equipment Required
Drilling equipment - any drilling equipment is acceptable that provides a reasonably clean　hole, which is at least 5 mm larger than the sampler or sampling rods, and less than 170mm diameter.
Barrel sampler - consists of 3 main parts; head, split-barrel and shoe, as shown in　below photo. A core catcher should be installed to prevent loss of sample. Shoes which have been damaged should be replaced or repaired.
Drive weight assembly - consisting of a 63.5 kg weight (hammer), a hammer lifter and a guide rod permitting free fall of 0.76 m and guide rod extension as shown in below photo.

3. Procedure of Standard Penetration Test (SPT)
3.1. Test Procedure
3.1.1. Test Hole
Drill the hole to the desired sampling depth and clean out all disturbed material. If a wet drill is used, flush out all cuttings.
3.1.2. Assembling Equipment
Attach the split-barrel sampler to the A-rod and lower into the hole until it is sitting on the undisturbed material.
Attach the drive weight assembly.
Lift the 63.5 kg hammer approximately 0.76 m and allow it to fall on the anvil delivering one seating blow.
Mark the drill rod in 3 successive 0.15 m increments to observe penetration.
Mark the drive weight assembly to indicate a 0.76 m hammer lift.
3.1.3. Penetration Testing
Raise and drop the hammer 0.76 m successively by means of the rope and cathead, using no more than 2 1/4 wraps around the cathead. The hammer should be operated between 40 and 60 blows per minute and should drop freely.
Continue the driving until either 0.45 m has been penetrated or 100 blows has been applied.
Record the number of blows for each .15 m of the penetration. The first 0.15 m increment is the "seating" drive. The sum of the blows for second and third increment of 0.15 m penetration is termed "penetration resistance or "N-value".
If the blow count exceeds 100 in total, terminate the test and record the number of blows for the last 0.30 m of penetration as the N-value.
If less than 0.30 m is penetrated in 100 blows, record the depth penetrated and the blow count. If the sampler advances below the bottom of the hole under its own weight, note this condition on the log.
3.1.4. Handling Sample
Bring the sampler to the surface and open it. Remove any obvious contamination from the ends or sides and drain excess water. Carefully scrape or slice along one side to expose fresh material and any stratification.
Record the length, composition, colour, stratification and condition of sample. Remove sample and wrap it or seal in a plastic bag to retain moisture. If the sample can be removed relatively intact, wrap it in several layers of plastic to strengthen it and seal ends with tape. Mark the sample "top" and "bottom" if applicable and label it with an identification number.