Effect of surcharge

TM 5-852-A/AFM 88-19, Chap. 4

d. The water content of a soil exerts a

b. In a field experiment on a silt subgrade near

substantial effect upon the depth of freeze or thaw

Fairbanks, Alaska, a series of 25-feet-square areas were

penetration which will occur with a given surface freezing

loaded to values ranging from 0 to 8 psi as shown in

28

figure 2-5 . Ventilation ducts were incorporated in the

or thawing index. An increase in moisture content tends

construction so as to achieve essentially equal depths of

to reduce penetration by increasing the volumetric latent

subgrade frost penetration in the test sections. As

heat of fusion, as well as the volumetric specific heat

shown in figure 2-6 the seasonal maximum frost heave

capacity. While increase in moisture content also

in this field experiment was reduced from about 0.5 feet

increases thermal conductivity, the effect of latent heat of

to about 0.3 feet with only a 2-psi applied surcharge load

fusion tends to be predominant.

and to less than 0. I feet with an 8-psi applied load.

c. Figure 2-7 presents the same data in the

2-4. Effect of surcharge.

form of total stress at the freezing interface (which

a. It has been demonstrated beyond question

includes weight of both frozen soil and applied

in both laboratory and field experiments that the rate of

surcharge) versus seasonal heave and frost penetration.

frost heaving is decreased by increase of loading on the

28,125,166

This type of presentation is more basic than that in figure

and that frost heaving can be

freezing plane

66

2-6 because it takes into account the total stress against

entirely restrained if sufficient pressure is applied . In

which ice segregation is acting at any point during the

foundation design the heave-reducing effect of load may

freezing. These data indicate that for 5 ft of seasonal

be readily taken advantage of by placing mats of non-

subgrade frost penetration an increase in total stress at

frost-susceptible materials on the surface of frost-

the freeze/thaw interface from 4 to 10 psi reduced

susceptible soils to reduce the magnitude of seasonal

seasonal frost heave from 0.4 to 0.15 feet.

frost heaving. Where the depth of winter freezing is not

d. On the plot of rate of heave versus applied

limited by the presence of underlying permafrost, the

loading

heave-reducing effect of such mats is not solely the

effect of load; it is also partly a result of the reduction of

subgrade frost penetration. The load imposed by the

structure and foundation members also contributes to

heave reduction.

U. S. Army Corps of Engineers

Figure 2-6. Heave vs frost penetration for various applied loadings, surcharge field experiment". See figure 2-5 for plan

and elevation of test installation.

2-8