Environmental Engineering Reference
In-Depth Information
Seepage Detection
Conditions of engineering significance include:
Flow through, around, and beneath earth dam embankments.
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Flow beneath and around concrete dams.
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Groundwater pollution as caused by flow from sanitary landfills, mine tailings
storage areas, chemical waste ponds, etc.
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Flows from slopes observable during site reconnaissance, depending on the season.
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Detection Methods
Tracers placed in a water body may be useful in locating entrance points of seepage and
detecting exit points. Nonradioactive tracers include fluorescent and nonfluorescent dyes.
Radioactive tracers include
82
Br and
131
I that are readily detectable with a Geiger-Muller
counter. Temperature can be sensed with a thermistor attached to the top of an insulated
aluminum-tipped probe inserted into the ground.
Acoustical emission monitoring
(Section 4.3.5)
may detect large flows.
2.4
Recovery of Samples and Cores
2.4.1
General
Objectives
Samples of geologic materials are recovered to allow detailed examination for identifica-
tion and classification, and to provide specimens for laboratory testing to obtain data on
their physical and engineering properties.
Sample Classes Based on Quality
Totally disturbed
samples are characterized by the complete destruction of fabric and struc-
ture and the mixing of materials such as that occurring in wash and auger samples.
Representative
samples are partially deformed. The engineering properties (strength,
compressibility, and permeability) are changed, but the original fabric and structure vary
from unchanged to distorted, and are still apparent. Such distortion occurs with split-bar-
rel samples.
Undisturbed
samples may display slight deformations around their perimeter, but for the
most part, the engineering properties are unchanged. Such results are obtained with tube
or block samples.
Sampler Selection
A number of factors are considered in the selection of samplers, including:
Sample use, which varies from general determination of material (wash sam-
pler), to examination of material and fabric and
in situ
testing (split-barrel sam-
pler), to performing laboratory index tests (split-barrel sampler), and to carrying
out laboratory engineering-properties tests (UD).
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Soil type, since some samplers are suited only for particular conditions, such as
soft to firm soils vs. hard soils.
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