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Report on
Construction of Porous Pavement in Pavilion Parking Area
Villanova University
William Heasom, July 13, 2006
Introduction
A porous asphalt parking area
(20 spaces) was constructed behind the Pavilion at Villanova
University as part of an extensive parking area renovation.
The area covered with porous pavement is shown (hatched) in
Fig. 1.
Figure 1
During construction,
representatives of Villanova University Urban Stormwater
Partnership (Emerson, Benford, and Heasom) were onsite to
observe the construction of the porous asphalt and to make
measurements of the prepared subgrade prior to the paving
operation. This was done so that the observed performance of
the pavement/storage bed/infiltrating subgrade may be
understood in terms of the soils underlying the improvement
as well as the geometry of the installation.
Site
Observation and Measurements
The contractor for this project
is Nason Construction and the paving subcontractor
responsible for the porous asphalt is H & K Group. Early on
June 6, 2006, the H & K had established the subgrade for the
porous parking area and was ready to begin placing the rock
for the storage bed. Figs. 2 shows the site just before the
placement of the storage bed rock and Fig. 3 shows the rock
being placed. Leo Kob of Villanova facilities pointed out
some pieces of filter fabric still embedded in the subgrade
(Fig. 4) which are remnants from the previously existing
parking area there, and the very compact nature of the
subgrade was noticeable. It was decided that, since this
project is an experiment and since there is value learning
from installations done under “real world” conditions, the
placement of the pavement should continue without attempting
to address some of the shortcomings of the prepared subgrade.
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
A series of four infiltrometer
measurements were made and bulk density samples were taken.
The double ring infiltrometer can be seen in Fig. 5 and the
locations and infiltration results can be seen in Fig. 6
with a tabular summary in Table 1.
Table 1
At this time, a series of
elevation measurements were made of the subgrade and of the
top of the existing curb (Fig. 6). The pavement and curb
cross section is given in Fig. 7.
During rainfall events, surface
water will flow from the tributary areas (to be determined)
around the pervious parking area and join with the rain
falling directly on the pervious pavement surface to fill
the void volume in the rock storage bed. A portion of this
inflow will be rapidly infiltrated, with the rest stored and
infiltrated more gradually over time. When the cumulative
inflow exceeds the storage volume, the system will surcharge
and deliver the overflow to the central inlet at the
surface. Two PVC pipes were installed during construction to
serve as auxiliary drains and as access points for a
pressure transducer so that the level of water in the
storage bed may be measured during storms. The elevation
measurements taken during construction allow the development
of the storage volume and wetted area vs. storage volume
relationships that are essential to understanding the
behavior of the system during rainfall events. The contours
interpolated from these elevation measurements are shown in
Fig. 8 and the derived stage-storage and stage-wetted area
relation is given in Table 2.
Figure 7
Figure 8
Table 2 |
