TM 5-818-4/AFM 88-5, Chap. 5
these readings usually form the basis to which subse-
Every effort should be made to schedule construction
so that this condition will be kept to a minimum, and
quent observations are related. Observations should be
plotted immediately after each set of readings is taken
protection must be required where necessary.
and evaluated for reasonableness against previous sets
i. Seismic zones. The design considerations for sub-
of readings. In this way, it is often possible to detect
surface structures subjected to dynamic loads caused
errors in readings and to obtain check readings before
by seismic activity or explosive devices are beyond the
significant changes in field conditions occur.
scope of this manual. Design details are provided in
(2) EM 1110-2-1908 discusses in detail various
TM 5-818-1/AFM 88-3, Chapter 7, and ER
types of instrumentation devices; procedures for in-
1110-2-1806. Specific problems relating to backfill
stallation, observation, and maintenance; collection,
operations are primarily limited to possible potential
recording, analysis, and reporting of data; and possible
for dynamically induced liquefaction. Certain materi-
source of error and causes of malfunctions.
als are particularly susceptible to liquefaction; these
include saturated gravels, sands, silts, and clayey
2-5. Optimum cost construction. The de-
sands and gravel. Where these materials are used as
signer should consider all details of the construction
backfill, the potential for liquefaction can be mini-
process to ensure a safe and operational facility at the
mized by requiring a high degree of compaction,
lowest possible cost.
particularly in critical areas such as beneath footings
a. Energy requirements. The consideration of ener-
and under the spring line of curved wall structures.
gy requirements is important not only for economical
The requirements for materials susceptible to liquefac-
reasons but also for the critical need to conserve ener-
tion are discussed in paragraph 3 - 3d.
gy wherever possible. It should not be the intent of the
design engineer to unduly restrict the competitive na-
2-4. Instrumentation. For important struc-
ture of current contractural procedures. Nevertheless,
tures of unique design or for structures where the po-
there are certain alternatives that the designer may
tential for postconstruction distress exists, instrumen-
specify that potentially could lead to more energy effi-
tation of the structure should be considered. The in-
cient construction with cost saving being reflected in
strumentation program may include monitoring the
bid prices. Some of the possible alternatives that
amount and rate of settlement, movement of retaining
should be considered are discussed below.
walls and other structural elements, development of
(1) Sources of suitable select backfill material
stresses within the structure, and development of hy-
should be located as close to the project site as possi-
drostatic and earth pressures against the structure.
ble. The source may be either a borrow area or a com-
Analysis of the data will furnish a check on design as-
mercial vendor.
sumptions and indicate what measures must be taken
(2) Hauling routes to and from the source of back-
to relieve or correct undesirable conditions before
fill and the project site should follow the most direct
distress develops. Information of this nature can also
route.
be of significant value in future design and construc-
(3) Only compaction equipment that will compact
tion.
the specific backfill to the required density in an effi-
a. Requirements. Specific requirements for instru-
cient manner should be approved for use. For large
ments are ruggedness, reliability over the projected
projects, the designer may require that the contractor
service life, and simplicity of construction, installa-
demonstrate the capabilities of the equipment he in-
tion, and observation. Other important considerations
tends to use prior to construction.
in selecting the type of instruments are cost and
(4) If possible, material from excavations or with-
availability. Manufacturers of devices considered for
in the immediate vicinity of the project site should be
installation should be asked to provide a list of projects
used as backfill, even though such material may be
on which their devices have been installed, and previ-
marginally suitable. The engineering characteristics of
ous users of new equipment should be contacted to as-
marginal material may be enhanced by the use of addi-
certain their operating experiences.
tives (para 3-3d).
(5) The energy requirements for adequate cold
weather protection of construction personnel and
A rational instrumentation program must use the
structures can be considerable. For project sites sub-
proper type of instruments and have the instruments
ject to seasonal cold weather, construction should not,
installed properly at critical locations. Valid readings
if possible, be scheduled during extreme cold weather
often depend on techniques and procedures used in in-
periods.
stalling and observing the instrumentation.
(1) Schedules for observations are generally estab-
b. Value engineering. Potential cost savings may be
lished by the design office. Initial observations should
realized by encouraging the contractor to participate
be checked to assure their validity and accuracy, since
in value engineering, whereby the contractor shares
2-9
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