Field sampling and testing - Geotechnical Investigation and Design Tables - page 40

Table 4.2 Boring types.

Boring type Uses

Solid stem auger Used in dry holes in competent materials. May need to use casing for

collapsing material.

Hollow stem auger Similar to solid stem (continuous flight) auger drilling, except hollow

stem is screwed into to ground and acts as casing. Sampling and
testing from inside of auger. Penetration in strong soils/gravel layers
difficult.

Wash boring Used to advance the borehole and keep the hole open below the

water table. Fluid may be mud (polymer) or water depending on the
soil conditions. Maintains hydrostatic head.

Rock coring Hardened cutting bit with a core barrel used to obtain intact rock

samples.

Air track probes Provides a rapid determination of rock quality/depth to rock based

on the time to advance the hole. Rock assessment is difficult as
rock chippings only obtained.

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Common drilling methods are presented in the Table.

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Maintaining a hydrostatic head below the water prevents blow out of the base of
the hole, with a resulting inconsistency in the SPT result.

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Similarly if the base of the hole is loosened by over washing in sands.

4.3 Field sampling
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Typical symbols only. Each consultant has his or her own variation.

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The symbols are used to speed up on site documentation.

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This requires an explanatory note on symbols to accompany any test record.

Table 4.3 Type of sampling.

Symbol Sample or test

TP Test pit sample

W Water sample

D Disturbed sample

B Bulk disturbed sample

SPT Standard penetration test sample

C Core sample

U (50) Undisturbed sample (50 mm diameter tube)

U (75) Undisturbed sample (75 mm diameter tube)

U (100) Undisturbed sample (100 mm diameter tube)

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The use of electronic hand held devices for logging, is becoming more popular.
These devices are useful for static situations such as existing rock cuttings and
exposures, or laboratory core logging.

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In dynamic situations such as field logging with a high production rate of
say 20metres/day, these electronic devices are not as efficient and flexible as