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SAWPlF.S ANO ■K Sili TESIS

Fig. 2 Example of reporting SPT test results. Key: S = SPT, SC = SPT (cone).

5. EXPLANATORY NOTES Notę 1. Clause 2.2.2.

The drive shoe of the SPT sampler is not designed to provide inside clearance with the sampling tubę. Hence, any significant inward distortion of the cutting edge shall not be permitted.

Notę 2. Clause 2.2.^.

Alternative designs of check valves are permitted provided they give equal or better performance.

Notę 3. Clause 2.3-1-

The stiffness of the rod used during testing is believed to affect the penetration resistance, especially because a light rod "whips" under the hammer blows.

Notę ^. Clause 2.4.l(a).

A loose anvil shall not be permitted. It is an advantage for the striking face of the anvil to be domed 3 mm in 100 mm (approxi-mately) to inhibit glancing blows between the drop weight and anvil.

Notę 5- Clause 2.4.1(c).

A hammer incorporating a self-tripping mechanism will overcome the effect of any friction in the lifting tackle and its use is recommended. A hammer with a free fali will give morę reproducible results and also smaller N values than a hammer operated by a friction winch with manilla ropę to lift and drop the hammer.

The self-tripping hammer should be raised slowly to ensure that the inertia of the hammer does not carry it above the pre-scribed level in excess of the prescribed free fali of 0.76 m(+0.02 m). Also, the pick-up assembly should be lowered slowly to avoid significant impact on the hammer.

A down-the-hole drive weight assembly acting directly on the sampler and mounted in a watertight chamber is permissible.

Notę 6. Clause 3-1-2.

To avoid hydraulic disturbance when boring in sand, the water pressure at the bottom of the borehole should correspond to the piezo-metric pressure in the surrounding ground at the test level. In artesian conditions, this will not be the same as the pressure corre-sponding to the standing water table.

Information on the water level in the layer(s)

tested shall be recorded. Particular attention should be given where artesian conditions are encountered, as is sometimes found when penetrating through an impervious layer into a pervious layer below water level. Any operation that give an opportunity for an upward flow of water to loosen the soil should also be recorded.

Notę 7- Clause 3-3-1-

The sample obtained with the SPT split-tube sampler is used for identification. It must be regarded as disturbed from the point of view of determining deformation or strength properties.

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