specs

Geotechnical Investigation South River Place, Gasser Drive, Napa 29 December 2010
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subgrade be proof rolled and observed for deflection by the Soils Engineer. Should
deflection/pumping conditions be encountered, supplemental recommendations will be provided.
It is noted that the near surface soils that will comprise the subgrade are considered moderately
to highly expansive or “active” per the City of Napa Standards (July 2008). According to the
City Standards, roads within the City right-of-way that have “active” subgrade soils will require
mitigation. Therefore, we recommended to over-excavate the active soils a depth of 6 inches, a
stabilization fabric such as a Mirafi 500X or equivalent be placed at the bottom, and the area
replaced with additional aggregate base rock. As an alternative, if it is desired to mitigate the
soils by chemical treatment, additional testing will be needed to determine the type of treatment
(lime and/or cement), depth of treatment and percent of product required.
Aggregate Base: All aggregate base material placed subsequently should also be compacted to a
minimum relative compaction of 95% based on the ASTM Test Procedure D1557. The
recommended aggregate base thicknesses for asphalt pavements are noted in the table below. The
minimum aggregate base thickness for portland cement concrete pavements is 6 compacted inches.
Asphalt Concrete: Based on the design R-Value of 15, and a range of traffic indices typical for a
mixed developments, the recommended pavement sections for asphalt concrete surfaces are
summarized in the table below. The appropriate traffic index (TI) should be determined by the
project Civil Engineer or City of Napa Standards.
Traffic Condition
Traffic Index
(TI)
Asphalt Concrete
(inches)
Class II Aggregate Base 1
(inches)
On-Site Pavements
Parking Stalls 4.5 2.5 8.5
Driveways 6.0 3.0 12.5
City Pavements
Hartle Court 7.0 4.0 19.0 2
NOTES:
(1) Minimum R-Value = 78
(2) Includes additional aggregate base for mitigation of active soils
(3) All layers in compacted thickness to CalTrans Standard Specifications.
Portland Cement Concrete: Where PCC pavement areas are utilized, the concrete should be poured
on the compacted aggregate base layer described above. The concrete should be a minimum of 6
inches thick and reinforced with a minimum of No.4 rebar spaced at 16 inches on center, each way.
Additional reinforcement may be required by the Structural Engineer.
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