Environmental Engineering Reference
In-Depth Information
Odex Drilling
Odex drilling is used to set casing in formations where hole collapse occurs and drilling
with mud is inefficient due to high mud loss. Such conditions include coarse and porous
soils, highly fractured rock, or rock with frequent cavities. It is also used to install mini-
piles socketed into rock.
The Odex drill includes casing with a bit, and an inner core barrel. When drilling a
reamer on the Odex bit swings out and drills a hole larger than the external diameter of
the casing. Cuttings are flushed from the casing with water or air. When the required
depth has been reached, the drill is reversed and the reamer swings to its minimum diam-
eter, allowing the bit to be lifted up through the casing, which remains in the hole. Rock
drilling continues with a drill bit or a core barrel. Data on rock quality can be monitored
electronically, providing measures on penetration rates, thrust on the bit, rotation torque,
rotation speed, fluid pressure, and cross section of the hole.
Pneumatic Percussion Drills (Air Track Rigs)
Air tracks
(Figure 2.55)
provide a rapid and efficient method of characterizing rock masses
in terms of quality. Rates of penetration per second are recorded; the harder the rock the
lower are the penetration rates as shown on the logs given in
Figure 2.56.
Rock chips,
removed by air pressure, can be examined at the hole entrance. Rock core borings should
be drilled for correlations.
Subaqueous Drilling
Various types of platforms for the drilling equipment and applications for subaqueous test
borings are given in
Section 2.4.4.
Planning and Executing a Test Boring Program
Equipment Selection
The study phase, terrain features and accessibility, geologic conditions, boring depths, and
the sample types required are considered when a test boring program is planned.
Boring Types
Exploratory borings
are normally performed first to determine general subsurface
conditions. Only disturbed samples, and at times rock cores, are obtained.
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Undisturbed sample borings
follow to obtain UD and perform
in situ
tests, usually
in cohesive soils.
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Core borings
are programmed to obtain rock cores.
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Boring Spacing
In the feasibility and preliminary studies, borings are located to explore surface boundaries
and stratigraphy as depicted on an engineering geology map. Additional borings may be
required for increased definition. Grid systems may be appropriate in uniform conditions
and, depending on the study area, size may range in spacing from 100 to 300 ft (30 to 100 m).
Final study programs depend upon the project type as follows:
Structures (buildings, industrial plants, etc.) in urban areas usually are required
by code to be investigated by borings at spacings that provide at least one bor-
ing for a given building area. In other than code-controlled areas, boring layout
depends on building configuration, and spacing is generally about 50 to 100 ft
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