COS Lutheran-CS 880613ALPHA TESTING,' INC.
An Alpha Services Group Company
2209 Wisconsin St., Suite I00
Dallas, Texas 75229
214/620-8911
Metro 263-4937
June 13, 1988
Christ Our Savior Lutheran Church
Building Committee
209 East Sandy Lake Road
Coppell, Texas 75019
Attention: Mr. Jim Olsen
Re: Geotechnical Investigation
SANCTUARY & EDUCATION BUILDING
COPPELL, TEXAS
ALPHA Report No. 88152
Gentlemen:
Submitted herewith is the report of our geotechntcal investigation at the site
of the referenced project. This study was authorized by Mr. Olsen on May 16,
lg88.
This report contains the results of our findings and an interpretation of the
subsurface conditions disclosed with respect to developing geotechnical
engineering design parameters for the project. Recommendations to aid design
and construction of foundations and other earth connected phases of this project
are also addressed.
We appreciate the opportunity to be of service to you on this project. If we
can be of further assistance, such as providing our materials testing services
during construction, please contact our office.
Very truly yours,
AK/DAL:gt
ALPHA TESTING, INC.
Ali Khalilian, P.E.
Geotechnical Engineer
~vid A. Lew s,
Manager of Engineering Services
Copies: (1) Client
(3) Clifton E. Owens & Associates
Consulli~:
for design of the post-tensioned slab. The edge moisture variation
distance (em) for post-tensioned slabs constructed at this site would
be about 5 ft according to information published by the Post Tension
Institute.
The slab should be designed with exterior and interior grade beams
rigid enough for the foundation system used. A net allowable soil
bearing pressure of 2 kips per sq ft may be used for design of all
grade beams bearing in natural soils. In cases where grade beams bear
on fill soils placed as recommended in Section 7.3, a reduced net
allowable soil bearing pressure of 1.5 kips per sq ft should be used
in selecting grade beam sizes. Also a moisture barrier of
polyethylene sheeting or similar material should be placed between the
slab and subgrade soils to retard moisture migration through the slab.
6.4 Pavements
The clay soils encountered near the existing ground surface will
probably constitute the subgrade for most of the parking and drive
areas. Therefore, it is recommended that these soils be improved
prior to construction of pavements.
It is recommended that the existing clay soils in drive and parking
areas be overexcavated to a depth equal to the thickness of the
pavement section (asphaltic concrete or reinforced concrete). The
'exposed surface of the clays should be scarified to a depth of at
least 6 inches and mixed with an estimated 6 to 8 percent of hydrated
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lime (by dry unit weight) in conformance with Texas Highway Department
Item 260. The actual amount of lime required should be determined by
additional laboratory tests. The soil-lime mixture should then be
compacted to at least 98 percent of Standard Proctor maximum dry
density (ASTM D 698) at or slightly above the optimum moisture
content. In all areas where hydrated lime is used to stabilize the
subgrade soils, routine Atterberg-limit tests should be performed to
assure that the resulting plasticity index of the soil-lime mixture is
at or below 12. The City of Coppell, Texas requires that plasticity
index of lime stabilized subgrade should be below 12.
California Bearing Ratio ICBR) tests have not been performed for this
specific project, but our previous experience with similar soils
indicates that the CBR value for lime stabilized clay will be in the
range of 25 to 30. The CBR value for the natural untreated clay will
be on the order of 3 to 4. Using the above CBR values, and assuming
normal traffic for a 15-year project life, we provide the following
pavement recommendations for the parkin9 and drive areas.
An asphaltic concrete pavement section constructed upon a lime
stabilized subgrade could consist of at least 5.0 inches of asphaltic
concrete, composed of 3.5 inches of binder under 1.5 inches of surface
course in light duty (automobile) traffic areas. In areas where heavy
truck traffic is expected, 6 inches of asphaltic concrete 14.5 inches
of binder and 1.5 inches of surface course) should be adequate.
In the event concrete pavements are used, the above recommended
procedure for mechanical lime stabilization would also be required.
Pavements could then consist of 5 inches of adequately reinforced
concrete in both light duty and heavy truck traffic areas. All
concrete for pavements should have a 28-day design strength of at
least 3,000 psi.
The calculations used to determine the required pavement thickness are
based on only physical and engineering properties of the materials and
conventional thickness determination procedures. Related civil design
factors such as subgrade drainage, shoulder support, cross-sectional
configurations, surface elevations, reinforcing steel, joint design
and environmental factors will significantly affect the service life
and must be included in the preparation of the constructed drawings
and specifications.
6.5 Drainage
Adequate drainage should be provided~ at the site to reduce seasonal
variations in moisture content of the foundation soils. All pavements
or sidewalks should be sloped away from the building to prevent
ponding of water around the foundation.
In order to enhance the performance of slabs underlain by select fill
at this site, it is essential that every reasonable precaution be
taken to inhibit infiltration of groundwater and surface water into
the select fill. Past problems have been noted with slabs underlain
by even extensive select fill thicknesses when poor drainage caused
saturation of the select fill. In this instance the select fill can
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