Park West CC(09)-CS 960214reed engineering
GEOTECHNICAL CONSULTANTS
February 14, 1996
Project No. 2700.1
Mr. Bud Niswonger
O'Brien Associates
4310 Harvest Hill Road
Suite 136, LB-161
Dallas, Texas 75230
Re: Parkwest Commerce Center - II
Airline Drive and Executive Drive
Coppell, Texas
Dear Mr. Niswonger:
Submitted here are recommendations regarding equivalent pavement
sections for the referenced project. Two pavement sections were
provided; a five-inch section for light-duty, and a six-inch
section for truck traffic. Both sections were designed for a non-
stabilized subgrade, city of Coppell requires a minimum six-inch
section over a lime-stabilized subgrade.
A five-inch, 3,000 pounds per square inch (psi) concrete pavement
over a non-stabilized subgrade provides an unlimited number of
repetitions for car and light truck traffic. Additional analysis
of various sections was therefore not performed.
The standard pavement in areas subject to truck traffic was
considered to consist of 6-inch thick, 3,000-psi compressive
strength concrete over 6 inches of lime-stabilized subgrade. The
analysis has consisted of determining the number of daily
repetitions of an equivalent 18-kip axle load and a 20-year design
life. The analysis followed procedures from the American
Association of State Highway Officials (AASHO) Interim Guide. A
copy of the AASHO design nomograph is attached as Plate 1.
Three pavement sections have been analyzed; the referenced
"standard" pavement, 6 inches of 4,000-psi concrete, and 7 inches
of 3,000-psi concrete. The latter two sections were analyzed
considering natural or unstabilized subgrade.
2424 STUTZ DRIVE · SUITE400 · DALLAS, TEXAS75235 · 214/350-5600 · (FAX) 214/350-0019
O'Brien Associates
Project No. 2700.1
February 14, 1996
Page 2
The first factor to be derived consists of the modulus of subgrade
reaction, k, for both the natural subgrade and on top of a six-inch
layer of lime stabilized. A value of 100 pounds per cubic inch
(pci) is recommended for the natural subgrade. Correlations
developed by the Federal Aviation Administration (FAA) for cement-
stabilized subgrade provide an effective k value, considering a 6-
inch stabilized subgrade of 210 pci. Two hundred pci was used for
the analysis. A copy of the FAA correlation is attached as Plate
2.
The second factor required to evaluate the sections consists of the
working stress of the concrete. This value is equal to 0.75
percent of the modulus of rupture (MR). Correlations between the
compressive strength and MR indicate that the MR can be
approximated as 9 times the square root of the compressive
strength. This analysis results in a working stress of 370 and 425
psi for the 3,000- and 4,000-psi concrete, respectively.
Application of the AASHO nomograph results in the derived
equivalent 18-kip axle loads shown below.
Pavement Section Equivalent l$-Kip Axle Loads/Day
6-inch, 3,000 psi concrete
over 6" lime
40
6" 4 000 psi concrete
, ,
over natural subgrade
4O
7" 3 000 psi concrete
f ,
over natural subgrade
70
As discussed above and as shown on Plate 1, the allowable daily
traffic is based on a 20-year design life. ~,~
Based on this analysis, 6 inches of 4,000-psiAconcreTM over a non-
lime-stabilized subgrade is the equivalent of 6 inches of 3,000-psi
concrete over 6 inches of lime-stabilized subgrad~ ~
O'Brien Associates
Project No. 2700.1
February 14, 1996
Page 3
We trust this information is sufficient for your use.
questions arise, do not hesitate to call.
If any
Sincerely,
GROUP, INC.
P.E.
RFR/apr
copies submitted: (1) O'Brien Associates/Mr. Bud Niswonger
(1) Myers & Crow Company, Ltd./Mr. Richard Crow
City of Coppell/Mr. Michael A. Martin