Environmental Engineering Reference
In-Depth Information
Overshot knob
Landing ring
Borehole
Drill pipe
Drill bit
Mechanical pawls
Remote memory
unit
Drilling fluid
Motor housing
Reaction vane
Soil formation
FIGURE 2.46
The Dolphin Remote Vane. (Courtesy of
Fugro.)
Vane blade
There are several disadvantages to mud slurry:
Hole closure may occur in soft soils or crushed, porous materials such as shell beds.
●
Relatively large pumps are required to circulate the slurry, particularly when
boring depths exceed 30 ft (10 m).
●
Mud-cased holes do not permit accurate water level readings, unless environmen-
tally friendly biodegradable muds are used. Such muds incorporate an organic
substance that degrades in a period of 24 to 48 h, allowing GWL measurements.
●
Excessive wear on pumps and other circulating equipment occurs unless sand
particles are removed in settling pits.
●
Mud may penetrate some soils and contaminate samples.
●
Mud loss is high in cavity-prone and highly fractured rock.
●
Grouting
is used where closure or hole collapse occurs in fractured or seamy zones in
rock masses. Cement grout is injected into the hole in the collapsing zone and then the hole
is redrilled.
