E. M. PART XV
CHAPTER 3
October 1954
Part XV
ARCTIC AND SUBARCTIC CONSTRUCTION
CHAPTER 3
RUNWAY AND ROAD DESIGN
3-01. GENERAL. The construction of satisfactory roads and runways in permafrost areas is normally more difficult than
in temperate regions because the imperviousness of the underlying permafrost tends to produce poor soil drainage
conditions, and because disturbance of the natural surface may set in motion adjustments in thermal regime, drainage,
and slope stability which may have serious and progressive consequences. Cuts should be avoided if possible, and side
slopes in fill composed of fine-grained materials should be kept to a 4 to 1 ratio or flatter.
a. Effect of subgrade soil conditions on design. The design of pavement sections is very dependent upon the type
of subgrade soils. Clean coarse-textured soils are subject to negligible heaving when frozen, and to only nominal
consolidation when thawed. Permafrost in such soil deposits is normally homogeneous and normally contains no
segregated ice. Design problems are simplified with such soils, as frost conditions do not alter their stability or bearing
capacity.
The danger of loss in bearing capacity upon thawing, and of heaving action upon freezing, is greatest in fine-
textured soils. Such action in a soil is dependent upon the availability of water, and to a large degree on void sizes, and
may be expressed as an empirical function of grain size, as follows:
Inorganic soils containing 3 percent or more of grains finer than 0.02 mm. in diameter by weight are
generally frost-susceptible. Although uniform sandy soils may have as high as 10 percent of grains finer
than 0.02 mm. by weight without being frost-susceptible, their tendency to occur interbedded with other
soils makes it generally impractical to consider them separately.
Soils in which ice segregation generally occurs when favorable ground water and freezing temperatures are
present have been classified in the following four groups, listed approximately in the order of increasing susceptibility to
frost heaving and/or weakening as a result of frost melting. The order of listing of subgroups under groups F3 and F4
does not necessarily indicate the order of susceptibility to frost heaving or weakening of these subgroups. There is some
overlapping of frost susceptibility between groups. The soils in group F4 are of especially high frost susceptibility. Soil
names are as defined in the Unified Soil Classification System.
Group
Description
F1
Gravelly soils containing between 3 to 20 percent finer than 0.02 mm. by weight.
F2
Sands containing between 3 and 15 percent finer than 0.02 mm. by weight.
F3
(a) Gravelly soils containing more than 20 percent finer than 0.02 mm. by weight. (b) Sands, except very fine
silty sands, containing more than 15 percent finer than 0.02 mm. by weight. (c) Clays with plasticity indexes
of more than 12. (d) Varved clays existing with uniform subgrade conditions.
F4
(a) All silts including sandy silts. (b) Very fine silty sands containing more than 15 percent finer than 0.02 mm. by
weight. (c) Clays with plasticity indexes of less than 12. (d) Varved clays existing with nonuniform subgrade
conditions.
Varved clays consist of alternate layers of inorganic silts and clays and in some instances fine sand. The thickness
of the layers rarely exceeds one-half inch, but occasionally very much thicker varves are encountered. They are likely to
combine the undesirable properties of both silts and soft clays. Varved clays are likely to soften more readily than
homogeneous clays with equal average water contents. However, local experience and conditions should be taken into
account, since under favorable conditions, as when insufficient moisture is available for significant ice segregation, there
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