TM 5-852-4/AFM 88-19, Chap. 4
CHAPTER 7
MONITORING PERFORMANCE
evidences of foundation distress.
Written and
7-1. General.
photographic records of inspections should be
a. Although periodic visual inspections are an
maintained so that the development of problems can be
essential part of performance monitoring, destructive
fixed in time. Additional instrumentation should be
trends may be present for several years before visual
installed when needed to assist inspection. A brittle
signs of foundation distress appear. Gradual warming of
plaster patch (tell-tale) placed over a crack will indicate if
frozen soil has little effect on performance until the
movements are continuing. Mechanical and electrical
melting point is reached. Severe damage can then
strain gages may also be considered. Inspection of
rapidly develop if the foundation has high ice content.
interconnecting utilities and adjacent areas is also
Exceptional weather conditions or changes in operation
important because leaks in utility lines, insufficient
may also induce more abrupt deviations. By installing
surface drainage provisions, disruption of natural ground
instrumentation, such efforts can be detected and
water, thermal disturbance and other factors may cause
stopped before damage results. If distress does occur,
unanticipated problems.
instrumentation provides the evidence needed to
establish the source of the problem which otherwise
must be defined by deductive reasoning, a process of
7-3. Vertical movement measurement.
limited value where unique foundation conditions are
a. Measurement points should be installed at
encountered.
the key points on the foundation so that frost heave or
b. Where possible, basic instrumentation for
settlement deflections can be monitored. The points
monitoring the performance of a foundation and structure
should be established during construction and their
should be installed prior to construction in conjunction
elevations referenced to a frost-free stable benchmark
with the program of subsurface exploration. Frost-free
(Chap 5) located some distance away in an undisturbed
benchmarks, temperature sensors, frost gauges, water
area. If an adequate benchmark is unavailable, the
wells and other devices installed in drill holes at that time
relative elevations of points on the structure should at
will define the undisturbed conditions as well as any
least be measured. Since it is not always possible to
subsequent changes caused by the facility. Additional
predict potential problem areas, the elevation of
instrumentation should be installed during the
numerous points on and around the foundation should
construction. The type and amount of instrumentation
be established initially. Subsequent surveys need not be
and the observational frequency depend on the type of
as comprehensive. If foundation movements do occur,
building and foundation, its purpose, and the subsurface
the pattern of measurement points can then be adjusted
and environmental conditions.
as needed. Allowance should be made for removal,
196
c. In 1943 Dr. Karl Terzaghi
wrote:
blockage and damage to points during the life of the
"Records with potentially valuable information have
structure by establishing enough points so as not to be
become worthless on account of a few omissions which
too dependent on any one.
escaped attention at the time the record was filed.
b. Although expensive, manometer systems
Others have never served a useful purpose because the
are occasionally used to measure the relative elevation
130
data were so poorly presented and cumbersome that no
of points on a structure . By interconnecting the upper
one could afford the time to unravel and digest them."
ends of the manometers with a hose, variations in
Consequently, well organized systems for data collection
atmospheric pressure from one point to the next can be
and analysis should be established at the time
eliminated. To avoid introducing errors caused by
instrumentation is installed and summary data reports
variations of liquid density with temperature, the
prepared periodically. Photographs taken before, during,
manometers should be maintained at the same
and after construction are often useful.
Broad
temperature, or temperatures should be measured and
comparisons and evaluations on a regional or extra-
corrections applied.
agency basis also provide extremely valuable input for
c. Under some conditions, such as where soil
development of new and improved criteria. Copies of
creep is occurring, measurement of horizontal
such data and reports should be submitted to CRREL for
components of movement may also be needed.
incorporation into its records under its mission of
7-4. Temperature sensing. Where remote sensing of
obtaining performance feedback, maintaining cognizance
temperature is necessary electrical systems are
and disseminating information on cold regions science
generally required. These are the most versatile and
and engineering.
most frequently used systems for monitoring freeze and
7-2.
Inspections.
Periodic inspection of the
thaw conditions in the ground. Either thermocouples or
performance of facilities is essential to detect possible
7-1
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