Environmental Education

POSITIVE
PHOTO BY DAMON DESSERT ROOF
BI DESIGN
This half-on-roof,
half-on-grade
NCAA-regulation
lacrosse/field hockey field
at Providence College
won an award for its
engineering.
was made to grade the higher
end of the site, construct a
multilevel parking garage and
span the field from grade to
the garage rooftop.
Adding a field alters the
typical design of a parking
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structure, notes Geoff Adams,
a principal with Stantec Inc.’s
San Francisco office, designer
of Berkeley’s Underhill parking
structure. Specifically, rainwater
is almost universally
drained from field-less
parking structures toward
the middle of the concrete
slab, whereas those with
fields must be slightly crowned
so water flows away from
the center. What made the
Providence project tricky,
says Richard Croswell, a
senior structural engineer
and principal with SMMA,
was that the different subbases
used at each end of the
parking structure (concrete
and native soils) required
different approaches to
solve drainage and settlement
issues, while at the same time
care had to be taken to make
field performance uniform.
The design team’s solution
was a perimeter trench drain
system that was utilized in
conjunction with a series of
perforated panel drains that
together allow water both to
drain through and run off the
surface. The focal point of
the designers’ efforts, however,
was the transition zone
where the parking structure
ends and the graded portion
of the field begins. At the
midpoint of the field, where
the waterproofed basement
wall signals the structure’s
terminus, three feet of superporous
drainage material was
added to the base of the wall,
and a heavily reinforced,
hinged concrete slab was
poured along the top of the
wall that extended 15 feet
over the compacted soil and