TM 5-852-4/AFM 88-19, Chap. 4
mistors accurate to 0.01 C (0.02 F), although under
phase of the frozen materials should first be identified;
field conditions with less than fully experienced
the material characteristics resulting from the frozen
observers, a lower order of accuracy may be obtained. A
state are then added to the soil description as
more detailed discussion of temperature sensors is
appropriate. Important ice strata found in the foundation
presented in chapter 7 (para 7-4). To obtain a good
are then described separately.
measure of the mean annual ground temperature, at
(2) Frozen soils are divided into two major
least one temperature installation should extend to a
groups: soils in which segregated ice is not visible to the
depth of about 30 feet. Readings during the period of
naked eye, and soils in which segregated ice is visible.
thermal stabilization following installation should be
The visual division is not necessarily determinative for
discounted. Readings during the summer and fall when
thaw settlement potential. The boundaries between
readings in the upper part of the foundation are at their
frozen and unfrozen strata should be carefully recorded,
warmest are most important. One or more of these
particularly in marginal permafrost areas. Surface cover
assemblies should be installed in areas which will not be
materials should be included in the exploration records
disturbed by the construction, in order to serve as a
and should be described especially carefully. Tests in
control against which ground temperatures in the
the field and/or laboratory such as for soil gradation and
construction area during and after construction may be
Atterberg Limits may be employed as needed to
compared.
supplement the field identification.
(2) The maximum seasonal depth of thaw
(3) The result will be an exploration log of
penetration can be readily measured at the end of
the type illustrated in figure 3-2, where an obvious thaw
summer or in early fall by probing, test pitting or other
settlement potential exists, as revealed by the ice layer
means, correlated with soil temperature readings.
from 7.7 to 9.1 feet. This information may by itself
(3) Thermocouple
and
thermistor
decisively limit the design options and determine the
assemblies are usually prefabricated in protective plastic
needs for further foundation data.
e.
Density and moisture content. The dry unit
tubing before delivery to the site.
Recommended
principles and techniques of subsurface temperature
weight and natural moisture contents of both frozen and
measurement are presented in a paper by Sohlberg;g2
unfrozen core samples or frozen lumps should be
his report includes an extensive bibliography.
determined. The bulk densities of representative frozen
c. Physiography and geology. Even if only a
core samples or frozen lumps should be first obtained.
single structure is involved, physiographic and geologic
Then the sample should be melted and the dry weight of
information on the general area should be established.
solids and the moisture content as a percent of dry unit
Information on the surrounding terrain will often be
weight obtained. This will give a plot of dry unit weight
invaluable in interpretation of the detailed exploration
and moisture content vs. depth as shown in figure 3-3.
results at the site itself. Bedrock exposures, glacial
From knowledge of the common moisture content
landforms, alluvial deposits and similar features should
ranges for the foundation materials encountered and
be known. Surface cover conditions of the site should
from the number and thicknesses of ice layers
also be recorded and are essential for estimating the
encountered, the existence of a potential settlement
extent of change in thermal regime which will be
problem in thawing may be immediately apparent if
produced by the construction. Topographic data are an
amounts of ice are appreciable. However, quantitative
essential requirement.
analysis of the amount of settlement which will occur can
d. Identification and classification of foundation
readily be made through the procedures outlined in f
materials. The most important single step in foundation
below.
(1) The maximum heave that can occur as
investigations is the accurate description and
a result of in-place freezing of the water present in the
classification of the exploration materials in accordance
voids of a non-frost-susceptible soil (without ice
with the Unified Soil Classification System MIL-STD
segregation) may be computed by the following formula:
619B including the frozen soil classification system.' The
frozen soil portion of this system has been devised on
∆H = 0.144wλdH x 10
-4
the basis of experience of United States and Canadian
(Equation 1)
167
organizations .
where
∆H = frost heave, ft
(1) The frozen soil classification system
provides information on the factors of appearance and
w = water content, percent of dry weight of soil
physical properties which are essential guides to the
∆d = dry unit weight of soil, lb/ft
3
nature and behavior of the material in the frozen state
H = thickness of deposit, ft.
and to the changes which may occur upon thawing. It is
(2) The expansion on freezing of non-
independent of geologic history or mode of origin on the
frost-susceptible soil is negligible under nominal
materials and can be used with any types of samples
which show the natural structure of the materials, such
as specimens recovered from drill holes or test pits, or
frozen in the laboratory. Unfrozen soils and the soil
3-5
Previous Page
