TM 5-852-4/AFM 88-19, Chap. 4
in figure 2-8, comparison is made between laboratory
performed and the field quantitative validity of this
and field test results for silt soils. While the results of the
WASHO clay curve has not been proved; however, there
two types of experiment correspond approximately in
is no question that clays should be less affected by
magnitude, the laboratory tests indicate a more rapid
surcharge than silts (see, for example, fig 2-9a). While
lowering of the rate of heave with increase in surcharge
laboratory data are available on several soils, little
than the field tests. It is believed that this may have
reliable field information is available on effect of
been caused by edge effects in the small laboratory
surcharge for other soils than the Fairbanks silt.
specimens; the field values are unquestionably more
Therefore, where advantage is taken of the effect of
representative of real construction situations.
surcharge and where justified by the scope and details of
e. Also shown in figure 2-8 are laboratory
the construction project, test footings of prototype
dimensions using the actual proposed loadings should
results for WASHO clay (liquid limit = 37.0 percent,
be constructed in order to obtain data on actual frost
plasticity index = 13.0 percent). The flatter curve
heave values which will occur. This is important not only
indicates less rapid reduction of heave with increase in
40
because of the differing behaviors
applied load than in the laboratory tests on silts . No
quantitative field-scale test on a clay subgrade has been
U. S. Army Corps of Engineers
Figure 2-7. Heave vs frost penetration for various total stresses, surcharge field experiment". See figure 2-5 for plan and
elevation of test in stallation.
2-9
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