Thaw Weakening and Load
Restriction Practices on
Low Volume Roads
MAUREEN A. KESTLER, THOMAS KNIGHT, AND AUDREY S. KRAT
Army Corps of Engineers pavement design pro-
INTRODUCTION
cedure includes designing for normal conditions,
Three conditions are necessary for the occur-
full or limited subgrade frost penetration (LSFP),
rence of ice segregation:
and reduced subgrade strength (RSS). The frost
1. The soil must be frost susceptible.
action trial design is typically selected based on
2. A water source must be available to the freez-
cost. In the case of many low volume roads, such
ing zone.
rigorous trial design procedures are not used.
3. Freezing temperatures must penetrate into the
Instead, roads evolve over the years as additional
soil.
gravel or asphalt concrete (AC) surfacing is added
Ice segregation itself is a complex interaction of
to fill in ruts or overlay cracks. Consequently, these
heat and moisture flow (U.S. Army and the Air
low volume roads (that are often built upon frost-
Force 1985). Negative pore pressures are gener-
susceptible subgrades) are highly susceptible to
ated at the freezing front, causing moisture to
damage from trafficking during thaw-weakened
migrate toward the front. This results in ice lens-
periods.
ing near the freezing front and frost heaving at
Techniques other than LSFP and RSS (to reduce
the pavement surface. During midwinter and
frost penetration and thaw weakening) are either
spring thaws, ice lenses melt both downward from
costly or require additional research. Incorporat-
the surface and upward from lower depths. Melt-
ing insulating layers, capillary cutoffs, or drain-
ing ice lenses leave the soil unconsolidated. Addi-
age layers can be costly for low volume design traf-
tionally, downward melting releases excess water
fic. Using reduced tire pressures (alone or in
that cannot drain through the underlying frozen
combination with load reductions and load restric-
layers. Consequently, support capacity is reduced,
tions) may provide another alternative method for
and the pavement system becomes susceptible to
reducing springtime damage to low volume roads
damage during trafficking. Figure 1 shows a typi-
(Bradley 1997, Davies et al. 1998, Kestler et al. 1998,
cal low volume road exhibiting signs of pavement
Mahoney et al. 1994, Moore 1997). However, even
distress from trafficking during spring thaw.
if research confirms the promising preliminary
results, regulatory and policy-making depart-
ments must determine methods for enforcement.
This will take time. Furthermore, using lower tire
PAVEMENT DESIGN IN SEASONAL
pressures may reduce, but will probably not elimi-
FROST AREAS
nate, the negative impact of traffic on thaw-
The pavement thickness design procedure for
weakened roads. Most states in the northern
high-traffic-volume highway and runway pave-
United States impose load restrictions on low
ments subjected to seasonal freezing should
volume roads during thaw-weakened periods.
include trial designs that account for the effects of
This practice, when properly imposed and en-
frost action (Yoder and Witczak 1975). The U.S.
forced, successfully minimizes springtime road
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