Ice Action on Riprap
Small-Scale Tests
DEVINDER S. SODHI, SHARON L. BORLAND AND JESSE M. STANLEY
INTRODUCTION
ing small-scale tests to assess the damage of riprap
According to the Coastal Engineering Research
by direct ice action, and present the results ob-
Center (1984), riprap is defined as a protective lay-
tained from this small-scale study.
er of quarry stones randomly placed to prevent
erosion, scour or sloughing of an embankment of
REVIEW OF SLOPE PROTECTION
bluff. As listed in the publication by Construction
IN THE COLD REGIONS
Industry Research and Information Association
A few (≈ 1020) man-made islands were built
(1991), the functions of a rock breakwater include
attenuation of wave transmission and overtopping,
since the 1970s for exploration of oil and gas along
dissipation of wave energy, and filtration. These
the southern coast of the Beaufort Sea. Innovative
two manuals contain extensive information on the
means of slope protection for the Arctic coastal and
design, construction and maintenance of the rock
offshore facilities were developed to minimize
structures, so that the structures can perform their
their construction costs. Other constraints associ-
intended tasks with acceptable risk of failure and
ated with the construction in that area are the short
maximum possible benefit-to-cost ratios. In Appen-
construction season and high costs of labor, equip-
dix A, we have presented the formulas to compute
ment and material.
the size of stones to be used for riprap protection
The presence of ice is the major difference be-
against waves (Coastal Engineering Research Cen-
tween the design of slope protection in the cold
ter 1984) and in a flood control channel (U.S. Army
and warm regions (Croasdale et al. 1988). During
Corps of Engineers 1991). However, the guidance
the winter months, the presence of ice limits the
for the design of shore protection systems in the
wave climate and erosion, but the ice itself may
cold regions, where ice is present, is limited. This
damage the slope protection system. When the ice
can largely be attributed to the small amount of
edge retreats during the summer months, zones
coastal construction in the cold regions and par-
of armor already damaged by ice may possibly
ticularly in the Arctic. Except for a few artificial
further be damaged because of storm-generated
islands built along the southern coast of Beaufort
waves in the open water. Three issues that may
Sea for exploration of oil and gas resources in the
affect the design of slope protection in the Arctic:
1970s and the 1980s, most of the construction of
1) an ice sheet may ride up the sloping surface and
dams and coastal facilities in the cold regions has
damage the surface facilities, 2) grounded rubble
taken place outside the Arctic areas.
ice around an island or adjacent to a beach may
As in the case of open water, the processes tak-
form a protective barrier between the moving ice
ing place between an advancing ice sheet and in-
and a structure, and 3) the interaction between a
dividual rocks in a riprap structure are not simple
discrete, thick ice feature and an underwater berm
to model theoretically. Small-scale physical model
of beach or island slope may absorb the energy of
study is one of the means to assess the suitability
the moving ice feature (Croasdale et al. 1988).
of riprap as a slope protection system against ice
These are illustrated in Figure 1.
action. In the following, we present a brief review
As shown in Figure 2, three types of slope pro-
of slope protection system employed for installa-
tection designs have been used for the Arctic:
tions in the cold regions, state the objectives of this
1) sacrificial beaches, 2) sandbag-retained islands,
study, describe the procedure followed in conduct-
and 3) caisson-retained islands (Croasdale et al.
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