ST9902-CS010816TEAGUE NALL AND PERKINS
ENGINEERS ~, SURVEYORS · CONSULTANTS
MEMORANDUM
TO:
FROM:
PROJECT:
DATE:
RE:
Ken Griffin, P.E.
City Engineer
Jed Sulak, P.E.
West Sandy Lake Road
August 16, 2001
Geotechnical Report
We have discussed your comments on the geotechnical report for W. Sandy Lake Road with
Charles Jackson of CMJ Engineering. Prior to Charles preparing a final report, we wanted to
brief you on the proposed changes to see if they adequately address your concerns.
Sub.qrade Improvement
The first sentence in section 4.2 is confusing because the "or" should be an "and". Based on
discussions with Charles, he is recommending that the sandy soils east of boring B-10 be
treated with cement and the clay soils west of boring B-10 be treated with lime.
The application rate quoted in the report is based on a 6-inch treated subgrade. Charles will
recalculate the application rate based on an 8-inch treated subgrade.
Pavement Thickness Calculations
Your comn'~ents on the pavement thickness calculations primarily involved the traffic
assumptions. At our last meeting, you provided us with Year 2010 traffic projections that we will
use in the calculations. These traffic volumes are higher and will require a thicker pavement
section.
You also questioned the percentage of trucks assumed on the west end of the project (west of
State Road). Based on discussions with Charles, we are proposing to increase the percentage
of trucks to 7% west of State Road. This percentage of trucks will also apply to Royal Lane.
We are proposing to calculate three (3) different concrete pavement sections. The limits of
each section and the major assumptions are listed below:
(1)
Sandy Lake Road from SH 121 to Coppell Road North
Traffic (ADT): 30,064 (Year 2010 projection)
Percent Trucks: 7% (4% 80-kip multi-axle trucks)
75 percent of traffic in design lane (for six-lane segment)
20-year service life 11oo MACON STREET
FORT WORTH, TEX,4S 76102
(817) 336-5773
fAX (817) 336 2813
(2)
Sandy Lake Road from Coppell Road North to Denton Tap Road
Traffic (ADT): 23,894 (Year 2010 projection)
Percent Trucks: 5% (2% 80-kip multi-axle trucks)
80 percent of traffic in design lane (for four-lane segment)
20-year service life
(3)
Royal Lane
Traffic (ADT): 4,836 (Year 2010 projection)
Percent Trucks: 7% (4% 80-kip multi-axle trucks)
80 percent of traffic in design lane (for four-lane segment)
20-year service life
If the calculated thickness is less than that of the existing Royal Lane (8 inches),
then we will propose to the 8 inches.
The other comment you had regarding the pavement design calculations was the assumption of
"no growth". We propose to use the Year 2010 traffic projections for the full 20-year service life
to account for the traffic growth in area.
Please let me know if the information presented above adequately addresses your comments
on the geotechnical report. If so, we will have CMJ Engineering prepare the final report. If you
have any questions or need additional information, please call me at 817-336-5773.