WA9302-CS 941215"EOTECHNICAL
E I GEE Consultants, Inc.
E ] NVIRONMENTAL
2540 Glenda Lane · Suite ]08 · Dallas, Texas 75229 · (2]4) 620-9791 · Fax (214) 620-9794
December 15, 1994
Mr. John W. Birkhoff, P.E.
Shimek, Jacobs & Finklea
8333 Douglas Avenue, Suite #820
Dallas, Texas 75225
RE: Report No. C-94-0102-1
At Grade Water Storage Tank
Coppell, Texas
Dear Mr. Birkhoff:
Per your written request dated November 29, 1994, we have reviewed Preload's cover letter dated
November 18, 1994 and the Preload-A-Gram dated November 17, 1994. The following comments
are made based .upon our review and present knowledge of the project:
1. Two foundation systems: drilled, east-in-place pier foundation and integral slab and grade
beam foundation are not equally acceptable. A pier foundation is more stable than a
shallow foundation because of the variability of near surface soils, changes that take place
due to seasonal moisture change, and groundwater having less effect on piers.
2. A shallow foundation is potentially feasible at the above referenced site based on our
investigation and test borings performed to date. However, associated potential risks such
as differential vertical soil movements (settlement and heave) due poor drainage around
and below the foundation system, variability of near surface soils/fill material, etc. are
much greater for a shallow foundation.
3. If a shallow foundation system is selected, the slab should be designed stiff enough to
withstand not only differential settlement due to the structure and water loading but also
heave in an unloaded condition (tank partially to fully empty during or after construction).
4. Refer to Item 6 of Preload-A-Gram: We do not recommend removal and replacement of
the top three (3) feet of existing soil with granular material (as previously recommended
in our report) without a below grade drainage system. Our experience indicates that
removal and replacement of top soils with highly permeable materials in a building area
~ghimek, Jacobs & FinIdea December 15, 1994
causes a tendency for accumulation of water beneath the foundation slab. This is
commonly referred to as the "bath tub effect". At this site, the highly expansive clays are
three (3) feet below the presently existing grade. In order to reduce the uplift pressure,
we recommend select fill on top of existing grade. This will reduce the potential for
heave and associated foundation distress when the tank is partially to fully empty during
and after construction. Details for placement of "select ~l" can be found in Chapter VI,
Item B, D. and G of our original report dated February 25, 1994.
5. Structural engineering is not one of our areas of expertise and therefore we have no
comment on the actual structural design of the tank.
If we can be of further assistance, please do not hesitate to contact our office.
Very truly yours,
GEE Consultants, Inc.
Gary G. Huang, Ph.D. Richard W. Ge~P~.]
Project Manager President ~..~&~,""X ....
Geotechnical Engineering Division
GGH:RWG/lej
Attachment
cc: Ken Griffin - City of Coppell
GEE Consultants, Inc. Report No. C-94-0102.1
Page 2