The use of piling for the abutments will provide

The
use of piling for the abutments will provide a prefabricated and high-quality
foundation with adequate structural integrity with minimum construction time
since the piles will be driven rapidly in the sandy ground and will be capable
of being loaded immediately.

As well as sandy
ground, there is also the problem of high water table. Abutment drainage will be necessary to prevent hydrostatic pressure and
frost pressure. Hydrostatic pressure, including both soil and water, can amount
to an equivalent fluid unit weight of soil of 85 pcf. (Wisconsin Dot, 2017) Online. Frost action, which can occur in silty backfill, may result
in extremely high pressures. On high abutments, these pressures will produce a
very large force which could result in structural damage or abutment movement
if not accounted for in the design. To prevent these additional pressures on
the abutments, it will be necessary to drain away whatever water accumulates
behind the body and wings. This will be accomplished using a pervious granular
fill on the inside face of the abutment. Pipe underdrain will be provided to
drain the fill located behind the abutment body and wings. For the future
rehabilitation of the structure, detailed plans will be provided to replace
inadequate underdrain systems. Semi-retaining abutments generally will be
overstressed or may slide if subject to large hydrostatic or frost pressures
unless accounted for in the design. Therefore, “Pipe Underdrain Wrapped 6-inch”
will be required behind all abutments. This pipe underdrain will be used behind
the abutment and outside the abutment to drain the water away. It is best to
place the pipe underdrain at the bottom of footing elevation as per standards.
However, if it is not possible to discharge the water to a lower elevation, the
pipe underdrain will be placed higher. Pipe underdrains can discharge water
during temperatures that are below zero. (Wisconsin Dot, 2017) Online

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