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FOC
E.O. CHURCH, INC.
I _ ENGINEERS & GEOLOGISTS
I:
SOILS AND FOUNDATION INVESTIGATION
PROPOSED ONECOMM
f, TOWER AND STRUCTURE
SW/4 , SECTION 11 , T1N, R66W
WELD COUNTY , COLORADO
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Prepared for:
�- ONECOMM, ATTN : LINDA AUGUSTINE
4643 SOUTH ULSTER STREET, SUITE 500
DENVER, CO 80237
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JOB NO. 5617 SEPTEMBER 16 , 1994
I• 950396
925 East 17th Avenue •Denver, Colorado 80218 P.O. Box 2869 • Evergreen, Colorado 80439
(303) 832-9692 FAX(303) 832-3517 (303) 674-0660 FAX (303) 671-0813
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�.' TABLE OF CONTENTS
SCOPE 1
CONCLUSIONS 1
PROPOSED CONSTRUCTION 1
SITE CONDITIONS 2
INVESTIGATIONS 2
SUBSURFACE CONDITIONS 3
TOWER FOUNDATIONS 3
LATERAL LOADS 3
SERVICE BUILDING FOUNDATIONS 4
SLAB-ON-GRADE CONSTRUCTION 4
SURFACE DRAINAGE 4
LIMITATIONS 5
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FIG . 1 - LOCATION OF EXPLORATORY BORINGS
FIG . 2 - LOGS OF EXPLORATORY BORINGS
FIG. 3 - SWELL-CONSOLIDATION TESTS
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950396
SCOPE
This report presents the results of a soils and foundation inves-
Ftigation for a ONECOMM Communication Tower and service building to be
located in the SW/4 , Section 11 , TIN, R66W, Weld County , Colorado . The
report presents a description of the subsurface conditions encountered
at the site , recommended foundation system, ground water , and design
and construction criteria influenced by the soils . The report is based
on data determined during the field and laboratory investigations and
our experience in the area . A summary of our findings and recommenda-
tions is presented below.
CONCLUSIONS
1 . Subsurface conditions encountered consisted of 1 foot of
silty clayey sand underlain by medium hard to hard claystone and
sandstone bedrock to the maximum depth explored of 15 and 30
Ifeet . The claystone bedrock exhibits a moderate swell potential .
2 . No free water was encountered in the borings at the time of
drilling .
3 . The tower should be founded on a drilled pier foundation .
Design and construction criteria are given in the report.
4 . The soils are suitable for slab-on-grade construction. We
recommend the slabs be free to move in the vertical direction .
5 . Good surface drainage should be established and maintained at
all times .
PROPOSED CONSTRUCTION
A 90 foot high free standing three sided latus type tower is
proposed as indicated on Fig . 1 . A 11' X 20' precast concrete vault ,
used as a service structure , will be located as indicated on Fig . 1 .
Relatively light construction loads are anticipated.
950396
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SITE CONDITIONS
The site is located in an agricultural area southeast of Fort
Lupton north and east of Roads 10 and 31 in Weld County, Colorado .
The site is adjacent to an existing electrical power easement and in-
cludes existing oil and natural gas equipment. The proposed tower and
structure will be located in the hilltop east of the power line ease-
ment . The site includes a gentle slope to the south with very little
vegetation . The hill top has been cut to provide pads for the oil and
gas pump equipment .
INVESTIGATIONS
Subsurface conditions were investigated by drilling 2 exploratory
borings at the location indicated on Fig. 1 . The borings were advanced
using a 4 inch diameter continuous flight auger powered by a Mobile B-
PI57 drilling rig . Samples were taken at general 5 foot intervals using
a California sampler which was driven into the soil by dropping a 140
pound hammer through a free fall of 30 inches . The California sampler
is a 2 . 5 inch outside diameter by 2 . 0 inch inside diameter device . The
number of blows required to drive the sampler into the soil is known
as a penetration test . The number of blows required for the sampler
to penetrate 12 inches can be evaluated and gives an indication of the
consistency or relative density of the soils and bedrock. The results
of penetration tests and logs of the soils encountered are presented
on the Logs of Exploratory Borings , Fig. 2 . Samples were returned to
the laboratory where they were visually classified and appropriate
testing assigned to evaluate the engineering properties of the soil
layers . Laboratory testing consisted of two swell-consolidation
tests . The results of the laboratory testing are presented on Figs .
2 and 3 .
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SUBSURFACE CONDITIONS
Subsurface conditions encountered consisted of 1 foot of silty
clayey sand underlain by medium hard to hard claystone and sandstone
bedrock to the maximum depth explored of 15 and 30 feet. The clay-
stone possesses a low to moderate swell potential . No free water was
encountered in the borings at the time of drilling .
TOWER FOUNDATIONS
We recommend the tower be constructed with a drilled pier founda-
tion system. The drilled pier foundation system can include one large
diameter pier ,or a series of three smaller diameter piers designed and
constructed to meet the following criteria .
1 . Piers should be designed for a maximum allowable end bearing
pressure of 25 , 000 pounds per square foot (PSF) and an allowable
skin friction of 2500 PSF for the portion of pier in bedrock . We
recommend a minimum deadload pressure of 15 , 000 PSF based on end
area only .
2 . The piers should have a minimum penetration into bedrock of
6 feet. We recommend a minimum length of piers of 18 feet.
3 . All piers should be reinforced full length with at least
three No. 5 bars to resist tension in the event of swelling .
Reinforcement should extend into grade beams of foundation walls .
4 . We believe piers can be installed using the "drill and pour"
method of drilling . Concrete must be onsite at the time of drill-
ing and placed immediately after drilling . Installation of the
piers should be observed by a representative of our office to
confirm piers are bottomed in suitable material and the holes are
properly cleaned.
LATERAL LOADS
The upper soils will react to lateral loading of the tower . We
recommend the top 3 feet of soil not be used in the analyzing of lat-
eral loads due to disturbed conditions . For this site, we recommend
an "active" equivalent fluid pressure of 40 pounds per cubic foot
(PCF) and a "passive" equivalent fluid pressure of 400 PCF .
950396
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4
SERVICE BUILDING FOUNDATIONS
The proposed service building is a prefabricated concrete struc-
ture . It is a rigid box type design that can tolerate differential
movement. We believe the building can be : 1 . placed directly on the
existing soil , 2 . placed on a concrete slab, 3 . constructed on a
spread footing foundation system or 4 . and drilled pier foundation .
If a permanent foundation is required, a spread footing foun-
dation system supported by the natural soils can be designed for a
maximum allowable soil bearing pressure of 2500 PSF. The most econom-
ical permanent foundation may be a drilled pier foundation . If a
drilled pier foundation is selected, the design criteria for the tower
should be used.
SLAB-ON-GRADE CONSTRUCTION
The upper soils encountered are suitable for slab-on-grade con-
struction. If new fill is required beneath slabs , we recommend the
onsite soils be compacted to a minimum of 95% of standard Proctor
density as determined by ASTM 698 . We recommend slabs be constructed
as "floating" slabs which are free to move in a vertical direction .
SURFACE DRAINAGE
The risk of wetting of foundation soils can be reduced by care-
fully planned and maintained surface drainage . We recommend the fol-
lowing precautions be observed during construction and be maintained
at all times after the structure is completed.
1 . Excessive wetting or drying of open foundation excavations
should be avoided as much as possible during construction.
2 . Backfill around foundation walls should be moistened and com-
pacted. Any settlement of backfill structure should be immedi-
ately filled and positive drainage re-established. 950396
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3 . The ground surface surrounding the exterior of the structure
should be sloped to drain away from the structure in all direc-
tions . We recommend a minimum slope of 12 inches in the first 10
feet .
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I 4 . Roof downspouts and drains should discharge well beyond the
limits of all backfill :
5 . Plastic membranes should not be used to cover the ground sur-
f face immediately surrounding the structure. These membranes tend
to trap moisture and prevent normal evaporation from occurring .
LIMITATIONS
IAlthough the borings were located to obtain a reasonably accurate
determination of foundation conditions , variations in the subsoil con-
ditions are always possible . If conditions different from those de-
scribed in this 'report are encountered in the completed excavation , we
Irecommend that the excavation be observed by a representative of our
office . The installation of piers should be observed by a representa-I tive of our office.
IIf we can be of further service in discussing the contents of
this report, or in the analysis of the influence of subsurface condi-
Itions on the design of the structure , please call .
IE. O . CHURCH , INC.
Edward O. Church, P. E.
2 copies sent
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cc : Kennith Clark , Architect
Icc : Structural Consultants , ATTN : Loren Lieberman
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I 950396
SW/4. SECTION II. TIN. R65W i( ' 1 ;1
WELD COUNTY. COLORADOc '' I_l
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PARTIAL SITE PLAN AND
OPLOCATION OF EXPLORATORY BORINGS
JOB H0. 5611
FIG I
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t_ CiL _,._-„A.i DSTONE BEDDROC ;, HARD. HOIST. GOL D. BROWN
— 6/I2 ?N,:;,.A -_- _ THAT 5 BLOWS OF A I40 POUND HAlt ER FALLi'JG 30
_ i(..!CHESv'J E;5 SECURED TI; DRIVE A 25� NCH 0 D SAMPLER C iMCHES,
' :0 IT I is PLDRA FOR' E C .IN -S WERE DRILL ED ON 9-8-N S I1
."TER Ei C Of I II PJ U S EI !G; T AUGER POWERED BY A B-57 MOBILE DRIL L ING RIG.
-REF WATER WAS EFICOUidTEIED AT TIE TII'1E OF DRILLING
3 ..J.: - WATER COMTPI (7;1
ET; - DRY DENSITY (PCFI
B NO. 5617 LOGS OF EXPLORATORY BORINGS
61)346
3 r f 1 1 l l
O 2 - EXPANSION UNDER CONSTANT
/ PRESSURE DUE TO WETTING
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0.1 0 1.0 10 100
APPLIED PRESSURE — ksf
Sample of CLAYSTONE from TH-1 @ 4 FEET
Natural Dry Unit Weight 115 pcf
Natural Moisture Content a 12 . 7 percent
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__-- EXPANSION UNDER CONSTANT
4 PRESSURE DUE TO WETTING
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0.1
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APPLIED PRESSURE — ksf
Sample of CLAYSTONE from TN-1 @ 9 FEET
Natural Dry Unit Weight = 104 pc f
Natural Moisture Content = 20. 2 percent
FIG . 3
JOB NO . 5 617• 95039(3
Swell- Consolidation Test Results
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