Environmental Engineering Reference
In-Depth Information
Many types of geologic materials have characteristic engineering properties, and values
are included throughout the chapter as well as elsewhere in the topic. The values are use-
ful for preliminary assessments and for the evaluation of the “reasonableness” of data
obtained from field and laboratory testing. Very often, such values are obtained from back-
analysis of a failure condition in the field.
Field Instrumentation
(Chapter 4
)
General
There are many instruments available to measure, either qualitatively or quantitatively,
surface and subsurface movements, strains, and
in situ
stresses and pressures. They range
from simple to complex, from low to high cost, from recoverable to expendable to perma-
nent. The selection depends on the importance of the work, the information required, and
the time available for installation and study.
Applications
Instruments are installed to provide information pertaining to the anticipation of the fail-
ure of natural or cut slopes, measurements of the settlement and heave of structures, con-
trol of preloading operations, anticipation of objectionable ground subsidence beneath
structures adjacent to excavations or over tunnels, control of the performance of earth
dams and tunnels, the monitoring of vibrations and seismic forces, and the investigation
of fault activity and surface warping. In many engineering projects, particularly braced
excavations, tunnels in rock, and steep cut slopes in open-pit mines, the monitoring of
deformations permits the use of economical contingent designs with low safety factors
and reduced construction costs. When deformations reach dangerous levels, as predeter-
mined by analysis, additional support can be added to arrest movements, or other proce-
dures invoked, in accordance with the contingency plans already prepared.
For monitoring subsidence over large areas and earthquake activity along faults, devel-
opments are being made in the applications of global positioning systems (GPS) and satel-
lite imagery, such as radar interferometry (difSAR).
1.2.3
Characteristics of Geologic Materials and Formations (Part II)
Rock and Soil: Identification and Classification
(Chapter 5
)
Rock types are described based on their identification characteristics of mineral content,
fabric, and texture, as having been originally formed as igneous, sedimentary, or meta-
morphic rocks. Rock-mass characteristics, as affected by discontinuities, are introduced to
permit presentation of rock-mass description and classification systems. It is the charac-
teristics of the
in situ
rock mass with its systems of discontinuities that normally control
response to changing stress fields.
Soils are described based on their general characteristics, mineralogy, and related engi-
neering properties. Mineralogy is more important than is often realized; not all sands are
composed of the essentially indestructible quartz grains, and clay activity depends to a
large extent on mineral composition. Classification systems are presented along with pro-
cedures for identifying and describing the various soil types.
Rock-Mass Characteristics (
Chapter 6
)
Rock masses, as originally formed, have characteristic forms, shapes, and structural fea-
tures that are related to rock type. Tectonic activity and other phenomena deform the rock
