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CTL /THOMPSON, INC.
CONSULTING ENGINEERS
SCOPE
This report presents the results of our geotechnical investigation for the
proposed Thabit Residence to be built at Tract 43, Antlers Orchard Subdivision in
Garfield County, Colorado. We explored subsurface conditions at the site to provide
foundation recommendations for the proposed building. This report includes a
description of the subsurface conditions found in our exploratory borings, a
recommended foundation system and geotechnical criteria for it, construction
criteria for details influenced by the subsoils, results of our percolation testing and
a design percolation rate. Our report was prepared from data developed during our
field exploration, laboratory testing, engineering analyses and our experience. A
summary of our conclusions is presented below.
SUMMARY OF CONCLUSIONS
1. Our exploratory borings penetrated a thin surficial layer of organic
silty sands above medium stiff to very stiff, silty to sandy clays with
occasional gravel and clayey sand lenses. In our TH -1 the clays were
above medium dense, sandy to clayey gravels underlain by medium
dense, silty to gravelly sands. No free ground water was found in our
exploratory borings during our field investigation.
2. We recommend founding the building with footings bearing on the
undisturbed natural, silty to sandy clays.
3. Slab -on -grade can bear on the natural, silty to sandy clays after
moisture conditioning and compacting as discussed under SITE
GRADING.
4. A ground surface slope away from the building should be maintained
at all times to reduce wetting of soils below foundations.
MR. ALLEN R. THABIT
THABIT RESIDENCE 1
CTLIT GS -2595
4. Frequent control joints should be provided. We suggest using the
recommendations outlined by the American Concrete Institute (ACI).
The above precautions will not prevent movement of slabs -on -grade floors in the
event the soils become wet, but they will reduce the potential damage when
movement occurs.
BASEMENT WALLS
A walkout basement is planned. Foundation walls will be subjected to lateral
earth pressures. Foundation walls are restrained and cannot move, therefore, they
should be designed for the "at- rest" lateral earth pressure. Assuming the on site
clays are used as backfill, we recommend using an equivalent fluid density of 50 pcf
to calculate the "at rest" lateral earth pressure. The above equivalent fluid density
does not include allowances for sloping backfill, hydrostatic pressures, live loads
or loads from adjacent structures.
Backfill of foundation walls can consist of the on site clays free of organics,
debris, rock larger than 4 inches in diameter or other deleterious materials. Backfill
should be moisture treated to within 2 percent of optimum moisture content and
compacted to at least 95 percent of standard Proctor maximum dry density (ASTM
D 698).
PERCOLATION TESTING
We performed percolation testing at the locations shown as P -1 through P -3
on Figure 1. Percolation test results are shown on Figure 8. We recommend using
a design percolation rate of 20 minutes per inch.
MR. ALLEN R. THABIT
THABIT RESIDENCE 6
CTLfT GS -2595
SURFACE DRAINAGE
Performance of foundations and concrete flatwork is influenced by moisture
conditions within the subgrade soils. Surface grading should cause rapid run -off of
surface water away from the building in all directions. The following precautions
should be observed during construction and maintained at all times after the
construction is completed:
1. Wetting or drying of the open excavation should be avoided;
2. Water should not be allowed to pond adjacent to the building. The
ground surface surrounding the building exterior should be sloped to
cause rapid run -off of surface water away from the building. We
recommend a finished ground surface slope of at least 12 inches in the
first 10 feet;
3. Plastic membranes should not be used to cover the ground surface
immediately surrounding the building. These membranes tend to trap
moisture and prevent normal evaporation from occurring. Geotextile
fabric such as Mirafi or Typar can be used on the ground surface
immediately surrounding the building for weed growth control while
allowing evaporation to occur;
4. Roof downspouts, drains and other water collection systems should
discharge well beyond the limits of all backfill. Splash blocks or
extensions should be provided at all discharge locations.
LIMITATIONS
Our exploratory borings were located to obtain a reasonably accurate picture
of the subsurface conditions. Variations in the subsurface conditions not indicated
by our exploratory borings will occur. We need to observe the completed excavation
to confirm the soils are as we anticipated from our exploratory. Placement and
compaction of fill and backfill should be observed and tested by a representative of
our firm during construction.
MR. ALLEN R. THABIT
THABIT RESIDENCE 7
CTL/T GS -2595
Our report is based on conditions disclosed by our exploratory borings,
results of laboratory testing, engineering analysis and our experience. Criteria
presented reflects the proposed building as we understand it. We should be advised
if the final design differs from our assumptions to permit us to re- evaluate our
conclusions and recommendations.
This investigation was conducted in a manner consistent with the level of care
and skill ordinarily exercised by members of our profession currently practicing
under similar conditions in the locality of this project. No other warranty, express
or implied, is made.
If we can be of further service or if you have questions regarding this report,
please call.
CTL /THOMPSON, 1 C. ua Re e e•' .y:
I
Wilson L. "Liv" :ow. rF O.' ' � \ t ` /,• `" 3.,.
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MR. ALLEN R. THABIT
THABIT RESIDENCE
CTLIT GS -2595 8
PROPOSED THABIT RESIDENCE
TRACT 43
ANTLERS ORCHARD SUBDIVISION
GARFIELD COUNTY, COLORADO
PROPE
BOUNDA
TH -1
PLANNED
BUILDING
ENVELOPE
0
P -2
PROFILE • • . P -1
W P -3
•
Co Soo le: 1"=100'
� �ry
/tit)
APPROXIMATE LOCATIONS OF EXPLORATORY BORINGS
Job No. GS -2595 Fig. 1
i i;1 1
7
6
5
4
3
2
0
NO MOV,EMENT UNDER CONSTANT
F'RESSLSRE;. DUE TO WETTING '..,
2
3
4
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2
te 6
C c
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0.1 1.o 10 100
APPLIED PRESSURE — KSF
Sample of CLAY. SANDY (CL)__ __ - -_ NAIURAL DRY UNIT WEIGHT = =_ 124 _PCF
From _ TH - 2 AT 14 F _ E E I NATURAL MOISTURE CONTENT= 12.8___
Swell Consolidation
JOB NO. GS -2595 Test Results FIG. 5
