Environmental Engineering Reference
In-Depth Information
FIGURE 2.76
Core drilling with a Failing Holemaster. Light drilling mud is necessary in the fractured limestone above the
water table to prevent drilling mud loss.
used for coring soft rock or rock with soil-filled fractures. Discharge occurs behind a metal
skirt separating the core from the discharging fluid, providing protection from erosion.
Common bit sizes and core diameters
are given in
Table 2.14.
The smaller diameters are
used in exploratory borings for rock identification or in good-quality rock, but when max-
imum core recovery is required in all rock types, NX cores or larger are obtained. In seamy
and fractured rock, core recovery improves with the larger diameters, and HX size is com-
monly used.
