Primrose-CS 950515
reed engineering
GEOTECHNICAL CONSULTANTS
Project No. 2291 ~ .~..
255 Parkway Boulevard
Coppell, Texas 75019
ATTN: Mr. Ken Griffith
City Engineer
Re:' Primrose'School~
- Heartz Boulevard an~ Parkway Boulevard
'... Coppell, Texas
Gentlemen:
Submitted here are recommendations regarding equivalent pavement
sections for the referenced project. It is our understanding the
City of Coppell ordinances require lime stabilization of both light
and heavy pavement subgrades.
The design section for light-duty pavement consists of 5 inches of
3,000 pounds per square inch (psi) concrete. Analysis indicates
this section will take unlimited repetitions of light car and truck
traffic. Lime stabilization below five-inch pavement within areas
subject to light-duty traffic is not required from an engineering
perspective.
The standard heavy-duty pavement 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 daily repetitions of an equivalent l$-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 · SUITE 400 · DALLAS, TEXAS 75235 · 214.'350-5600 · (FAX) 214:350-0019
City of Coppell
Project No. 2291
May 8, 1995
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 pavement 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 E~uivalent 18-Kip Axle Loads/Day
6-inch, 3,000-psi concrete
over 6" lime 40
__~ 6-inch, 4,000-psi concrete
.~. over natural subgrade 40
7-inch, 3,000-psi concrete
over natUral subgrade 70
As discussed above and as shown on Plate i, ~he allowable daily
traffic is based on a 20-year design life.
Based on this analysis, 6 inches of 4,000-psi concrete over a non-
lime-stabilized subgrade is the equivalent of 6 inches of 3,000-psi
,/~ concrete over 6 inches of lime-stabilized subgrade.
o q-,.c.
City of Coppell
Project No. 2291
May 8, 1995
Page 3
We trust this information is sufficient for your use. If any
questions arise, do not hesitate to call.
Sincerely,
REED ENGINEERING GROU~ INC.
RFR/apr
copies submitted: ~(2) City of Coppell/Mr. Ken Griffith
(1) c/o A.I.G., Inc./Mr. Ken Reimer