Environmental Engineering Reference
In-Depth Information
FIGURE 2.53
Several types of drilling bits. From left to right: three-bladed soil-cutting bits, tricone roller rock-cutting bits,
carbolog-tooth bits for cutting soft rock, and diamond rock-coring bit.
4.
Take sample.
5.
Advance hole through the next interval of 5 ft (or 1 m) by either driving casing
and removing the soils, as in step 3, or using a mud slurry or the hollow-stem
auger to retain the hole, and take sample.
6.
Continue sequences until prescribed final boring depth is reached. (In deep bor-
ings, or supplemental boring programs, sampling intervals are often increased to
10 or even 20 ft [3-6 m].)
7.
When rock is encountered, set casing to the rock surface to permit coring with
clean water to keep the bit cool and clean and prevent clogging.
8.
Record casing lengths; measure and record drill rod and bit length and drill rod
and sample tool length each time that the hole is entered to ensure that the hole
bottom is reached, that the hole is not collapsing if uncased and that the sampler
is at the required depth below the casing or final boring depth prior to sampling.
Other Drilling Machines and Methods
Continuous Hollow-Stem Auger (ASTM 5784-95)
The hollow-stem auger has been used with increasing frequency in recent years to avoid
the use of drilling muds to retain the hole
(Figure 2.51).
Its use, therefore, is common for
environmental investigations. During advance, the auger flights remove the soil from the
hole and the hollow stem serves as casing. A bottom bit cuts the soil and a removable plug
on a rod prevents soil from rising in the hollow portion of the stem
(Figure 2.54).
At sam-
pling depth, the inner rods and plug are removed and either disturbed (SPT) samples or
undisturbed tube samples can be obtained. In “clean” sands and silts below the water
table, pressure equalization by filling the stem with water is usually necessary to prevent
the saturated soils from entering the auger. Drilling is difficult or impossible in very hard
