Environmental Engineering Reference
In-Depth Information
Boring Surveillance (Inspection)
During all phases of the boring program experienced surveillance should be provided to
ensure that the intent of the specifications is properly interpreted and executed, and that
the desired results are achieved.
Functions of the person performing the surveillance are generally as follows:
1.
Enforce the specifications.
2.
Maintain liaison with the structural engineer-architect and modify the program
as necessary (add or delete borings, change types, depths and intervals of sam-
pling, etc.).
3.
Ensure complete and reliable drilling information (accurate reporting of depths,
proper drilling, and sampling techniques).
4.
Identify accurately all geologic conditions encountered and prepare reports and
field logs that include all pertinent information
(Section 2.4.7)
.
Some conditions where experienced geologic interpretations are necessary include:
Differentiating a fill from a natural deposit. Some granular fills may appear to be
natural, when in reality they overlie a thin organic stratum, or contain zones of
trash and rubbish. Mistakenly identifying a deposit as fill can result in unneces-
sarily costly foundations when local building codes prohibit foundations on fill.
●
Judging the recovered sample material to be wash remaining in the casing rather
than undisturbed soil.
●
Determining groundwater conditions.
●
Differentiating boulders from bedrock on the basis of rock identification (boul-
ders may be of a rock type different from the underlying bedrock, especially in
glaciated terrain).
●
Supplemental Information
Many types of devices are available for use in boreholes to remotely sense and log various
subsurface conditions, which should be considered in the planning of any subsurface
exploration program, as described in
Section 2.3.6
.
2.3.6
Borehole Remote-Sensing and Logging
A number of devices and instruments can be lowered into boreholes to obtain a variety of
information. They are particularly useful for investigating geologic conditions in materi-
als from which it is difficult or impossible to obtain UD, such as cohesionless granular soils
and badly fractured rock masses. Applications, equipment, operation, and limitations of
various devices for remotely sensing and logging boreholes are summarized in
Table 2.15.
Borehole cameras
(TV and photographic) furnish images of borehole walls in fractured
rock masses.
Seisviewer
, an ultrasonic acoustical device, is also used to obtain images of borehole
walls in fractured rock masses.
The 3-D velocity probe
(
Figure 2.57)
ranges up to 15 ft in length, 3 in. in diameter, and
about 150 lb in weight. It is lowered into the borehole to measure compression and shear-
wave velocities, which provide information on fracture patterns in rock masses and, with
the gamma-gamma probe for density measurements, provide the basis for computing
dynamic properties. The 3-D sonic logger was so named because the records show the
amplitude and arrival times of the sonic energy for a given travel distance (between the
