HomeMy WebLinkAboutSoils Report 04.22.1994"Nov.20. 20031 5:18PM
H -P GE07ECH
H1 PWOTTW-PAWLAx GEOTECuNTC.&L, INC.
April 22, 1994
Chet Pohle
810 Bonita Drive
Aspen, Colorado 81611
No 6853 P. 11=.11/11
5(1211 Road iAsa
Ciaenwoad Sprints. (NI xiI1
Fax 303 945-6454
Mune 303 445-79613
Job No. 194 178
Subject: Subsoil Study for Foundation Design, Proposed Residence, Homestead
#36, Panorama Ranch, Ga teld County, Colorado.
Dear Chet:"
As requested, Hopworth-Pawlak Geotechnical, Inc. performed a subsoil study tor
design of foundations at the subject site. The study was conducted in accordance with
our agreement for geotechnical engineering services to you dated March 30, 1994. The
data obtained and our recommendations based on the proposed construction and
subsurface conditions encountered are presented in this report.
Proposed Construction: Plans for the site were conceptual at the dine of our study.
The proposed residence Will generaily be 2 stories of wood frame construction above a
walkout basement level and located between the explo€atory pits shown on Fig. 1. The
garage will be detached from the residence. Ground floor will be slab -on -grade. Cut
depths are expected to range between about 3 to 8 Leet. 1"uundation loadings for this
type of construction are assumed to be relatively light.
Yf building conditions or foundation loadings are significantly different firom those
described above, we should be notified to reevaluate the recommendations presented in
this report.
Site Conditions: The site was vacant and covered with grass, weeds and sage brush.
Numerous basalt cobbles and boulders were exposed on the ground surface. The terrain
is hilly with a moderate slope generaily down to the west within the building area. A
small ridge crosses through the building area in an east -west trending direction.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating two exploratory pits at the approximate locations shown on Fig. 1_ The lags
of the pits are presented on Fig. 2. The subsoils encountered, below about 1 to 2 feet
Tnrni n I
"�Nov.20 2003-5:14PM
Chet Pohle
April 22, 1994
Page 2
H -P GEOTECH
No.8853 P. 2x.02.'11
of rocky topsoil, consist of basalt gravels, cobbles and boulders in a highly calcareous
sandy silt matrix. Results of gradation analyses performed on samples of the subsoils
(minus 3 -inch fraction) obtained from the site are presented on Fig. 3. No free water
was observed in the pits at the time of excavation and the soils were slightly moist,
Foundation Recommendations:
Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread
footings placed on the undisturbed natural soil designed for an allowable soil bearing
pressure of 2,300 psf for support of the proposed residence. Sctticmcnta should be
relatively minor with some differential settlement risk if the bearing soils become
wetted. Footings should be a minimum width of 16 inches for continuous walls and
2 feet for columns. Loose and disturbed soils at the foundation bearing level within the
excavation should be removed to expose the undisturbed natural soils. Voids created by
boulder removal should be backfilled with concrete or compacted base course. Exterior
footings should be provided with adequate cover above their bearing elevations for frost
protection. Placement of footings at least 36 inches below the exterior grade is
typically used in this area. 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 be designed to resist a
lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for the
on-site soli as backfill (excluding plus 6 -inch size rock).
Floor Slabs: The natural onsite soils, exclusive of topsoil, are suitable to support
lightly loaded slab -on -grade construction. 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 requirements for joint
spacing and stab reinforcement should be established by the designer based on
experience and the intended slab use. A minimum 4 -inch layer of tree -draining gravel
H -P G OTECK
14(Nov.20. 2003L` 5:14PM
1 y
Chet Pohle
April 22, 1994
Page 3
H -P GEOTECH
No.8853 P. 3 . 3'11
should be placed beneath basement level slabs to facilitate drainage. This material
should consist of minus 2 -inch aggregate with less than SO% passing the No. 4 sieve
and less than 2% passing the No. 200 sieve.
A11 fill materials for support of floor slabs should be compacted to ac least 95% of
maximum, standard Proctor density at a moisture content near optimum. Required till
can consist of the on-site soils devoid of vegetation. topsoil and oversized rock.
Underdr4lrt System: Although free water was not encountered during our exploration,
it has been our experience in the area that local perched groundwater may develop
during times of heavy precipitation or seasonal runoff_ Frozen ground during spring
runoff can create a perched condition. We recommend below grade construction, such
as retaining walls, crawl space and basement areas, be protected from wetting and
hydrostatic pressure buildup by an.underdrain system.
The drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free -draining granular material. The drain
should be placed at each level of excavation and at least 1 foot below lowest adjacent
finish grade and sloped at a minimum 1% to a suitable gravity outtat, Free -draining
granular material used in die underdrain system should contain Tess than 2% passing the
No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of
2 inches. The drain gravel backfill should be at least 1 U2 feet deep.
Surface Drainage: The following drainage precautions should be observed during
construction and maintained at all times after the residence has been completed:
1) Inundation of the £uuralation excavations and underslab areas should be avoided
during construction.
H -P GEQTECH
"(Nov.20. 2003I5:15PM
Chet Pohle
April 22, 1994
Page 4
H -P GEOTECH
No.8B53 P. 4P.04'11
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 ha landscape
areas. Free -draining wall backfill should be capped with at least 2 feet of the
onsite, finer graded soils to reduce surface water infiltration.
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 12 inches in the first 1.0 feet in unpaved areas and a minimum slope of
3 incites in the first 10 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Percolation Testing: A profile pit (Pit 2) and three percolation tests were conducted
to evaluate the feasibility of an infiltration septic system at the site. The log of the
exploratory pit is shown on Fig. 2 and the perootation test results are presented in Table
11. Based on our findings, the tested area is suirable for an infiltration septic disposal
system. The system should be based in the calcareous subsoils encountered below 2
feet_
Limitations: This report has been prepared in accordance with generally accepted
geotechnical engineering principles and practices in this area at this time. We make no
other warranty either expressed or implied. The conclusions and recommendations
submitted in this report are based upon the data obtained from the exploratory pits
excavated at the locations indicated on Fig. 1, the proposed type of construction and our
experience in the area. Uur findings include interpolation and extrapolation of the
subsurface conditions identified at the exploratory pits and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions
H.p GEOTacH
NcNov.20. 2003` 5:15PM
Chet Pohle
April 22, 1994
Page 5
H -P GEDTECH
No.8853 P. 5'•x/11
encountered during construction appear different from those described in this report, we
should be notified at once so 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 aot,responsible for technical interpretations by others of vur information. As
the project evolves, we should provide continued consultation and field services during
constr ction to review and monitor the implementation of our recon nidations, 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 till by a representative of the soil engineer.
`�•-� If you have any questions or if we may be of further assistance, please call our office.
Sincerely,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Steven L. Pawlak, P.E.
Reviewed By:
Daniel E. Hardin, P.E.
SLY/ro
Attachments
W -P GaoTEc►w
OCNov.20. 2003• i:16PM
H -P GEOTECH
No.8853 P. 6'.x/11
34 -
prop
0d Ottve` 4
Approximate Scale
1" $2 20'
Building
Pit 1 • Envelope
\ \
. Set back line
Umiak
• Exploratory Pit
d Percolation Test Hole
•
/N
194 1
y1HEPWORTH-PAWLAK
GEOTECHNICAL. Inc.
Location of Exploratory Pits Fig, 1
NcNov.20. 2003` 5:16PM
H -P GEOTECH
HEPWORTH-FAWLAK GEOTECHNICAL, INC.
LOG OF EXPLORATORY HOLES
Job No: 194 178
Datum: Ground Surface
Type/Size of Hole: Cat 426 4x4 9ackhoe
No.8853 P. 7°.07'11
Prepared By: LEE, H -P Geotech, inc. Date: 03/31/94
Reviewed [3y: SLP, H -P Geotech, Inc. Date: 04/18194
Pit No: 1
Lo -Klein: Uphill side of residence
Pit No: 2
Location: Downhill side of residence
Depth,Ft.
Visual
Description of
Depth,Ft.
Visual
Description of
Cl
Material
Class.
Material
0 - 1 ,
OL
'Topsoil; sandy clay and silt,
cobbles and small boulders, dark
brown, roots.
0 - 2
OL
Topsoil; sandy clay attd silt,
cobbles and small boulders, dark
Brown, roots.
1 - 6
GM
Gravel; cobbles and boulders;
sandy silt matrix, medium dense,
slightly moist. wbitc. highly
calcareous. basalt rock.
2 - 8
GM
Gravel; cobbles and boulders;
sandy silt matrix, medium dense,
slightly moist, white, highly
calcareous. basalt rock.
Practical Refusal 96 feet.
Bottom, of !alt 8 feet.
No free water.
No free water.
UltnWILU
Samg =
4 - 5
GM
Disturbed bulk
3 - 4
GM
Disturbed bulk
1. -.
-
..✓--.....i.w,e-----ftmmmwmonarm
Notes:
1. Exploratory pits were dug on March 31, 1994 with a backhoe.
2. Locations of exploratory pits were measured approximately by pacing from features shown on the
site plan provided.
3. Elevations of exploratory pits were not measured and logs of exploratory pits are drawn to depth,
4. The exploratory pit locations should be considered accurate only to the degree unplied by the
method used.
No free water was encountered in the pits at the time of excavation. Fluctuations in water level
may occur with time.
Fig. 2
Nov.20 20031 5:t6PM
H—P GEOTECH
No.8853 P 8 P.aa/za
HIYCCICMETEli At/At Y1 8
SIEVE ANALYSIS
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HEPWORTH-PAWLAK GEOTECHNICAL, WC.
JOB NO. 194 178
TA BLE 1
SUMMARY OF LABORATORY TEST RESULTS
mac.,—
SAMPLE MAIMS
NATURAL
MOISTURE
CONTENT
MI
!NATURAL
DRY
CESSPIT
AHI
GRADATION
PERCENT
PASSING
NO.200
SIEVE
ASTERISM LUIS
UMCCMIFRIED
COMPRESSIVE
SIAEMWM
MS
SOIL OR
BEDROCK TYPE
NT
OEPIH
PM!
GRAVEL
1%)
SAND
1961
MUM
UNIT
IV
PLASTIC
INDEX
19L1
1
4-5
69
21
10
silty sandy gravel
•
2
3-4
47
40
13
46
Nt'
silty sandy gravel
!
I
1
1
L-
•
-
-- --r
_, .._._.
z
rn
HD .LO3E d-H
Nov .20. 20031 5:18PM H P GEOTECH
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 11
PERCOLATION TEST RESULTS
No 8853 P. 10P.terit
JOB NO. 194 178
HOLE NO.
4
HOLE DEPTH
(INcHES)
LENGTH OF
INTERVAL
(MINI
WATER MIN
AT START OF
INTERVAL
(INCHES)
WATER DEPTH
Al ENO OF
INTERVAL
(INCHES)
DROP IN
WATER
LEVEL
LINCHES)
AVERAGE
PERCOLATION
RATE
(MIN./INCH)
+ P-1
•
'
23
19
refill
10
8 314
1 114
20
9 7/8
9 1/8
3/4
10 118
..._.
9 3/8
314
10 1/8
LL
9 318
3/4
—
10 1/8
9 3/8
314
P-2
33
15
refill
'.
11
9 3(4
1 1/4
20
10 112
9 3/4
3/4
(
10 3/4
10
2/4
11
10 1/4
3/4
11
10 1/4
314
I
P-3
32
15
Mill
10
8 314
1 1/4
30
10 1/8
9 31s
3/4
10 5/8
9 718
3/4
10518
97/8
3/4
10 5/8
10 118
1/2
Note: Percolation holes were excavated and soaked on March 31, 1994 and the tests were
conducted on April 1, 1994,
t•Nov.20. 20031 5:14PM
H -P GEOTECH
GJ'tech
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No.8853 P. 1 P.01/11
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b 2O CoLU Uy Road 154
uhuiwOcid sprineN, CoIarncla E1501
Phone: 970-945-79SE
Fax: y /U•45-8454
e-mn11: hp9uo@nivOcro rch•com
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