HomeMy WebLinkAboutSoils ReportGec�tecF,
HEPWORTH-PAWLAK GEOTECHNICAL
1-Ic1' firth-r.nclal
5020 Couni Road 154
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Phone: 9)710.945_ iotis
F.,. 970 945-6454
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UPDATED SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED POWER SUBSTATION EXPANSION
XCEL ENERGY SYSTEM OPERATIONS, RIFLE HEADQUARTERS
620 COUNTY ROAD 319
GARFIELD COUNTY, COLORADO
JOB NO. 107 0304
JULY 13, 2007
PREPARED FOR:
J.F. SATO AND ASSOCIATES
ATTN: GREGG EELLS, P.E.
5898 SOUTH RAPP STREET
LITTLETON, COLORADO 80120
Parker 303-84I-7119 • Colorado Springs 719-633-5562 • Silverchorne 970-468-1989
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FLOORSLABS. -4-
SURFACE DRAINAGE - 5 -
LIMITATIONS - 5 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURES 2 to 4- LOGS OF EXPLORATORY BORINGS
FIGURE 5 - LEGEND AND NOTES
FIGURES 6 to 9 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
PURPOSE AND SCOPE OF STUDY
This report presents an update of the subsoil study for the proposed expansion to the
existing power substation located at the Xcel Energy System Operations Rifle
Headquarters, 620 County Road 319, Garfield County, Colorado. The project site is
shown on Figure 1. The purpose of the study was to develop recommendations for
foundation design. The study was conducted in accordance with our agreement for
geotechnical engineering services to J.F. Sato and Associates dated April 30, 2007. We
previously drilled two borings at the site and provided foundation recommendations in a
report dated May 15, 2007, Job No. 107 0304.
A field exploration program consisting of a total of ten exploratory borings was
conducted to obtain information on the subsurface conditions. Samples of the subsoils
obtained during the field exploration were tested in the laboratory to determine their
classification, compressibility or swell and other engineering characteristics. The results
of the field exploration and laboratory testing were analyzed to develop recommendations
for foundation types, depths and allowable pressures for the proposed building
foundation. This report summarizes the data obtained during the Geld exploration and
presents our conclusions, design recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The proposed facility expansion will consist of an addition to the existing control
building, installation of a new duct bank and future enlargement of the existing substation
pad at the northeast side. The proposed building addition will be a tall, single story of
steel frame/metal skin construction and be attached to the north side of the existing
control building. Ground floor will be slab -on -grade. A duct bank will be located just
east of the building. Grading for the structures is expected to be relatively minor with cut
depths between about 2 to 5 feet below the existing ground surface. We assume relatively
light to moderate foundation loadings, typical of the proposed type of construction.
Job No. 107 0304 i.T .
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If building loadings, location or grading plans change significantly from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The project area consists of an existing power substation as shown on Figure I. The
substation equipment is located mostly on a level, fenced pad with control buildings
located just outside the west side and southwest corner of the fenced area. Grading for
the equipment pad consists of some cut at the south end and fill up to about 5 to 6 feet
deep at the north end. The ground surface in undisturbed areas is relatively flat to slightly
irregular with a gentle slope down to the north. The fill slopes are graded at about 20%.
Vegetation consists of weeds and scattered brush in undisturbed areas.
FIELD EXPLORATION
The field exploration for the project was conducted on May 3 (Borings 1 and 2), and June
27 and 28, 2007 (Borings 3 through 10). The exploratory borings were drilled at the
locations shown on Figure 1 to evaluate the subsurface conditions. One boring was not
drilled at the proposed building addition due 10 buried utility conflicts. The borings were
advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted
CME -45B drill rig. The borings were logged and monitored for groundwater by a
representative of Hepworth-Pawlak Geotechnical, Inc.
Samples of the subsoils were taken with a 2 inch L.D. spoon sampler. The sampler was
driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method
D-1586. The penetration resistance values are an indication of the relative density or
consistency of the subsoils and hardness of the bedrock. Depths at which the samples
were taken and the penetration resistance values are shown on the Logs of Exploratory
Borings, Figures 2 through 4. The samples were returned to our laboratory for review by
the project engineer and testing.
Job No. 107 0304 r, i..ip _ _
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils generally consist of stratified sand, silt and clay with scattered gravel size
sandstone fragments. About 1 to 2 feet of existing fill was encountered above the natural
soils in the proposed building addition area. Up to about 8 feet of existing fill was
encountered in Borings 5 through 7 drilled at the northeast corner of the existing pad.
Relatively dense gravel alluvium was encountered below the fine grained soils at a depth
of 48 feet in Boring 1 and extended down to the maximum explored depth of 51 feet.
Weathered to very hard sandstone bedrock was encountered below the fine grained soils
at depths of 30 to 34 feet in Borings 2 and 10. Drilling in the sandstone bedrock with
auger equipment was difficult due to the hardness of the rock and possible cemented
zone, and drilling refusal was encountered at a depth of 38 and 41 feet in the deposit.
Laboratory testing performed on samples obtained from the borings included natural
moisture content, density and percent finer than No. 200 sieve (silt and clay fraction)
gradation analyses. Results of swell -consolidation testing performed on relatively
undisturbed drive samples, presented on Figures 6 through 9, generally indicate low to
moderate compressibility under conditions of loading and wetting. The samples showed
a variable collapse/expansion potential after wetting. The laboratory testing is
summarized in Table I.
No free water was encountered in the borings at the time of drilling or in Borings l and 2
when checked 13 days later and the subsoils were slightly moist to moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, we recommend the building addition and duct
supports be founded with spread footings bearing on the natural soils.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
Job No. 1070304 Ggraech
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1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,500 psf. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this
section will be about 1 inch or less. There could be some additional
differential foundation settlement/heave if the bearing soils are wetted.
The bearing conditions should be further evaluated at the time of
construction.
2) The footings should have a minimum width of 18 inches for continuous
walls and 2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided
with adequate soil cover above their bearing elevation for frost protection,
Placement of foundations at least 36 inches below exterior grade is
typically used in this area.
4) Continuous foundation walls should be reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12
feet. Foundation walls acting as retaining structures should also be
designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least 55 pcf for the on-site soil as backfill. A sliding
coefficient of 0.35 and passive earth pressure of 300 pcf equivalent fluid
unit weight, can be used to resist lateral forces on the foundation.
5) All existing fill, topsoil and any loose or disturbed soils should be removed
and the footing bearing Ievel extended down to undisturbed natural soils.
The exposed soils in footing areas should be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -
on -grade construction. The soils possess a variable settlement/heave potential and there
is some risk of slab distress if the subgrade soils are wetted. To reduce the effects of
some differential movement, floor slabs should be separated from all bearing walls and
columns with expansion joints which allow unrestrained vertical movement. Floor slab
control joints should be used to reduce damage due to shrinkage cracking. The
Job No. 107 0304
requirements for joint spacing and slab reinforcement should be established by the
designer based on experience and the intended slab use. A minimum 4 inch layer of sand
and gravel (road base) should be placed beneath interior slabs for slab support. This
material should consist of minus 2 inch aggregate with at least 50% retained on the No. 4
sieve and less than 12% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of
maximum standard Proctor density at near optimum moisture content. Required fill can
consist of the on-site soils or imported granular soils (such as road base) devoid of
vegetation, topsoil and oversized rock.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and
maintained at all times after the addition has been completed:
1) Inundation of the foundation excavations and underslab areas should be
avoided during construction.
2) Exterior backfill should be adjusted to near optimum moisture and
compacted to at least 95% of the maximum standard Proctor density in
pavement and slab areas and to at least 90% of the maximum standard
Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. We
recommend a minimum slope of 6 inches in the first 10 feet in unpaved
areas and a minimum slope of 2'/2 inches in the first 10 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping that requires regular heavy irrigation, such as sod, should be
located at least 5 feet from the foundation on xeroscape should be used to
limit the potential for wetted below structures.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. We make no warranty either
Job No. 107 0304 A ap
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express or implied. The conclusions and recommendations submitted in this report are
based upon the data obtained from the exploratory borings drilled at the locations
indicated on Figure 1, the proposed type of construction and our experience in the area.
Our findings include interpolation and extrapolation of the subsurface conditions
identified at the exploratory borings and variations in the subsurface conditions may not
become evident until excavation is performed. It -conditions encountered during
construction appear different from those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We
are not responsible for technical interpretations by others of our information. As the
project evolves, we should provide continued consultation and field services during
construction to review and monitor the implementation of our recommendations, and to
verify that the recommendations have been appropriately interpreted. Significant design
changes may require additional analysis or modifications to the recommendations
presented herein. We recommend on-site observation of excavations and foundation
bearing strata and testing of structural Ell by a representative of the geotechnical
engineer.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Trevor L. Knell, P.E.
Reviewed by:
Steven L. Pawlak, P.E.
TLK/vad
Job No. 107 0304 Gech
BORING 1
BORING 3
•
R BORING 4
O
N
+n
EXISTING
ELECTRIC
TRANSFORMER
EXISTING
CONTROL
BUILDING
(SHADED)
EXISTING
SUBSTATION
FACILITY
NOTE: Site survey and topographic Information provided byJ F Soso
andAsroefates. Far boring location purposes only. Not for construction.
107 0304
Gtech
HEPWORTWPAWW( GEO'ECHHICAI.
LOCATION OF EXPLORATORY BORINGS
FIGURE 1
— 5470
5460
5450
...._, 5440
x--
5430
5420
5410
BORING 1
ELEV.=5468.5'
12/12
WC. 12.6
DD- 115
6/12
10/12
WC -11.4
DD- 117
.200=59
21/12
13/12
20/0
BORING 2
ELEV.=5463.5'
18/12
WC -3.2
DD=104
27/12
41/12
WC -5.4
DD.= 122
63/12
Note: Explanation of symbols is shown on Figure 5.
5470 —
5460
5450 —
5440
5430
5420
5410
W
0
Q
w
107 0304
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HEPW0WWPAWLAIC GEOTECHNICAL.
LOGS OF EXPLORATORY BORINGS
FIGURE 2
ELEVATION - FEET
5470
5465
5460
5455
.._ 5450
5445
BORING 3 BORING 4 BORING 5
ELEV.=5468.5' ELEV.=5469.5' ELEV.=5470
i
32222,—µ,C-13,5 ,
DD=114
200-91 / 8/12
J 12/12 WC=1
D0-113
0- 3
WC= -200.4
141
-200=94
DD=111
4
� , 7112
7
7/12
13/12
20/12 /
J7/12
14/12
/
01 18/12
4/12
BORING 6
ELEV.=5470'
6/12
WC=178
0D=106
9/12
WC=17.6 r pJ WC=15.6
00=106 D0=114
UC -500 /
5470
5465
/ I ' _
✓ / 17/12 11/12 5460
1
00- 5
• 11
/ -200=87 , —
•
f /
10/12 ' 1W12 X55
•
2
,
7 19/12 ^ 20/12 5450 ,�.^
J I
Note. Explanation of symbols is shown on Figure 5.
5445
ELEVATION - FEET
107 0304
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HEPWORTH-PA191AK GEC/TECHNICAL
LOGS OF EXPLORATORY BORINGS
FIGURE 3
•
5470
- 5465
5460
5455
- 5450
5445
BORING 7
ELEV. =5470'
R
8/12
j
i
11/12
WC -11.4
DO=112
•200=93
10/12
18/12
16/12
BORING 8
ELEV.=5464.5'
T
16/12
35/12
WC -4.9
DD=120
-200-64
45/12
50/12
BORING 9
ELEV. =5467'
r
16/12
WC=3.7
1:11)=100
-200-91
27/12
70/10
85/9
BORING 10
ELEV.=5468.5'
35/12
24/12
24/12
WC=5.3
00=107
-200=90
46/12
5470
5465
WC -6.6
D0=120
-200-94
5460
5455
5450
5445
5440 / 5440
130/12
- 5435 5435
5430 5430
Note: Explanation of symbols is shown on Figure 5.
30/0
Bollom of Boring
at 5427 5'
107 0304
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HEPWORIH-PAWW( GEOTECHNICAL
LOGS OF EXPLORATORY BORINGS
FIGURE 4
LEGEND:
MFILL; sandy clay with gravel, firm, moist, brown.
7
1
11
CLAY AND SILT (CL -ML); sandy to very sandy with depth, stiff and moist to hard and slightly moist, brown to Tight
brown, slightly calcareous, low plasticity,
SILT (ML), sandy to very silty sand, medium stiff to stiff at Boring 1 to very stiff and hard at Boring 2, slightly moist
to moist, light brown to brown, slightly calcareous.
SAND AND CLAY (SC -CL); with occasional gravel size sandstone fragments, medium dense/very stiff, moist, dark
brown, low plasticity.
GRAVEL AND COBBLES (GM); silty, sandy, dense, moist, brown, subrounded rocks.
SANDSTONE BEDROCK; weathered to very hard and cemented with depth, slightly moist, Tight brown. Wasatch
Formation
Relatively undisturbed drive sample; 2 -inch I.D. California liner sample.
Drive sample blow count; indicates that 6 blows of 140 pound hammer falling 30 inches were required to drive the
6/12 California sampler 12 inches.
Practical drilling refusal in cemented sandstone.
T
NOTES:
1. Borings 1 and 2 were drilled on May 3, 2007 and Borings 3 through 10 were drilled on June 27 and 28, 2007 with
4 -inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by taping from features shown on the site plan
provided by J.F. Sato and Associates.
3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided.
4. The exploratory boring locations and elevations should be considered accurate only to the degree implied by the
method used.
5. The lines between materials shown on the exploratory boring Togs represent the approximate boundaries between
material types and transitions may be gradual.
6. No tree water was encountered in the borings at the time of drilling or in Borings 1 and 2 when checked 13 days later.
Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (% )
DD = Dry Density ( pcf )
-200 = Percent passing No. 200 sieve
UC = Unconfined Compressive Strength (psf )
107 0304
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HEPWO(rTH•PAWUU( GEOTECHNICAL
LEGEND AND NOTES
FIGURE 5
COMPRESSION (% )
COMPRESSION (% )
0
1
2
0
1
2
3
0
0
107 0304
APPLIED PRESSURE (ksf )
Moisture Content = 12.6 percent
Dry Density = 115 pcf
Sample of: Sandy Clayey Silt
From Boring 1 at 5 Feet
•
Compression
upon
wetting
•
No movement
upon wetting
a
•
.1 1.0
10 10(
.1
1 0
10 10
APPLIED PRESSURE (ksf )
Gec�stech
HEPWURT PAWIAK GEOTECHHICA
APPLIED PRESSURE (ksf )
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 6
Moisture Content = 11.4 percent
Dry Density = 117 pcf
Sample of: Sandy Clayey Silt
From. Boring 1 at 15 Feet
•
Compression
upon
wetting
•
a
•
.1 1.0
10 10(
Gec�stech
HEPWURT PAWIAK GEOTECHHICA
APPLIED PRESSURE (ksf )
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 6
COMPRESSION (% )
COMPRESSION - EXPANSION (% )
0
1
2
3
2
1
0
1
2
0
0
APPLIED PRESSURE ( ksf )
Moisture Content = 3.2 percent
Dry Density = 104 pcf
Sample of: Sandy Silt
From. Boring 2 at 5 Feet
--"------------o...i._______-----7
-"--
-
C
Compression
upon
wetting
(..............,
""-•-...........Expansion
-
upon
wetting
1 1.0
10 1a
1
1.0 10 101
APPLIED PRESSURE ( ksf )
APPLIED PRESSURE ( ksf )
107 0304
I.
Gec5tech
NEPWORTHPAWLAK GEGlECNNIC*L
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 7
Moisture Content = 5.4 percent
Dry Density = 122 pcf
Sample of: Sandy Silty Clay
From Boring 2 at 15 Feet
-
(..............,
""-•-...........Expansion
-
upon
wetting
1 1.0
10 1a
APPLIED PRESSURE ( ksf )
107 0304
I.
Gec5tech
NEPWORTHPAWLAK GEGlECNNIC*L
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 7
COMPRESSION (% )
COMPRESSION - EXPANSION (% )
0
1
2
1
0
1
2
0
0
APPUED PRESSURE (ksf )
Moisture Content = 14.1 percent
Dry Density = 111 pcf
Sample of Sandy Clay
From Bor'ng 3 at 5 Feet
Sample of: Sandy Clay
From. Boring 6 at 5 Feet
.7-----"-"--°---.,ct.,.....,...,........__._....._..._._
7
---------
No movement
upon wetting
'
Expansion
upon
wetting
1
1.0 10 101
APPUED PRESSURE (ksf )
APPUED PRESSURE (ksf )
107 0304
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HEPAORTHhPAWLAII 1 EOTEDNICAL
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 8
Moisture Content = 15.6 percent
Dry Density = 114 pct
Sample of: Sandy Clay
From. Boring 6 at 5 Feet
7
---------
'
Expansion
upon
wetting
1 1.0
10 10(
APPUED PRESSURE (ksf )
107 0304
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HEPAORTHhPAWLAII 1 EOTEDNICAL
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 8
COMPRESSION - EXPANSION (%)
COMPRESSION - EXPANSION (% )
2
1
0
1
2
3
2
1
0
1
2
0
0
APPLIED PRESSURE ( ksf )
Moisture Content = 4.9 percent
Dry Density = 120 pcf
Sample of: Sandy Clay
From. Boring 8 at 10 Feet
(:).-"\NI:\
1___0
Expansion
upon
wetting
pension
upon
wetting
_
,
.1 1.0 10 10
APPLIED PRESSURE ( ksf )
APPLIED PRESSURE ( ksf )
107 0304
GecPtech
HEPWOfTTH-PAWLAK GEOTECHNICAL
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 9
Moisture Content = 6.6 percent
Dry Density = 120 pcf
Sample of: Slightly Sandy Clay
From Boring 10 at 21/2 Feet
pension
upon
wetting
_
,
,1
1.0 10 10
APPLIED PRESSURE ( ksf )
107 0304
GecPtech
HEPWOfTTH-PAWLAK GEOTECHNICAL
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 9
Job No. 107 0304
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