Willow Park-CS110916 September 16, 2011
Mr. Jason Rose
JR Rose Development
1207 Bethel School Court
Coppell, Texas 75019
Re: Willow Park Townhomes
Proposed Street Paving Subgrade
Coppell, Texas
Rone Project No. 1116815
Dear Mr. Rose,
Rone Engineering Services, Ltd. (Rone) previously conducted a
geotechnical engineering study for the referenced development. At the
present time, Rone is providing the construction materials testing and
inspection services. As part of Rone's current scope of work, soil samples
from the pavement subgrade were obtained to evaluate for the possible
addition of lime or cement as a subgrade stabilization procedure. Rone has
been asked to provide a recommendation for subgrade preparation to be
submitted to the City for review and acceptance. This letter presents our
recommendation for subgrade preparation. Results of the field and
laboratory testing will be submitted separately.
The exposed soil subgrade along the pavement right -of -way is comprised
of clayey sand fill with small pieces of brick, rock, concrete and other
construction debris. The inorganic construction debris was considered
acceptable for use as fill in the pavement subgrade provided particle sizes
were limited to 4 inches or less. In order to ascertain the most suitable
treatment method, Atterberg limits of the untreated sample were
determined. The plasticity Index (PI) as determined by the Atterberg limits
analysis was 12. Due to the granular, sandy nature of the soil, a lime series
was deemed impractical and would be ineffective for the soils as
represented by the sample obtained by Rone.
A cement series was then completed on the sample and 4 percent cement
was determined to provide suitable subgrade improvement. Cement is
typically utilized to improve soft, sandy pavement subgrade and provides an
extra layer of strength and support beneath the concrete pavement section.
Shrinkage and swelling of the exposed subgrade is considered to be
relatively insignificant based on the PI value. In addition, when analyzed
using standard pavement design software, such as Darwin, equivalent
structural performance is achieved by utilizing cement stabilization, or
adding 1 inch to the concrete pavement section.
JR Rose Development
September 16, 2011
Rone Project No. 1116815
Page #2
We understand the development is a small number of residential townhomes and that traffic will
be limited to automobiles, construction vehicles associated with residential construction, trash
trucks, school buses and occasional moving vans. We further understand the pavement was
originally designed as a 6 inch concrete pavement over a 6 inch lime treated subgrade. As
stated above, lime treatment is considered impractical for this site due to the low plasticity soils
encountered. Therefore, Rone recommends the proposed concrete section be increased by 1
inch and subgrade treatment be eliminated. As an alternative, addition of 4 percent of cement
by dray weight may also be considered for subgrade treatment. If the cement treatment method
is selected, the pavement section may remain at 6 inches.
Subgrade preparation and compaction should follow the recommendations provided in the
original geotechnical study prepared by Rone. Rone personnel should observe subgrade
preparation activities to verify no debris larger than 4 inches is utilized in the fill and to perform
in -place soil density testing of the compacted subgrade.
We appreciate this opportunity to be of continued service for this project. Please do not hesitate
to contact us should you have questions regarding the information presented in this letter, or if
you require further assistance.
Sincerely,
Mark D. Gray, P.E.
Vice President
Texas Engineering Firm Registration Number F -1572