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HEPWORTH - PAWLAK GEOTECHNICAL
February 28, 2006
Justin Sanford
200 Mountain Shadow
Glenwood Springs, Colorado 81601
Hepworth-Fawlak Gentechn cal, Inc
5020 County Road 154
Glenwood Springs, Colorado 81601
Phone. 970.945-7988
Fax 970.945-8454
email: hpgen@hpgeorech.com
Job No.106 0179
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 76, Filing
7, Elk Spnngs Subdivision, Garfield County, Colorado
Dear Mr. Sanford:
As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design
of foundations at the subject site. The study was conducted in accordance with our
agreement for geotechnical engineering services to you dated February 16, 2006. The
data obtained and our recommendations based on the proposed construction and
subsurface conditions encountered are presented in this report. Hepworth-Pawlak
Geotechnical, Inc. previously conducted a preliminary geotechnical study for Filing 7 of
Elk Springs (formerly Los Amigos) and presented our findings in a report dated February
14, 1997, Job No. 196 617.
Proposed Construction: Plans for the proposed residence are conceptual at this time
and this report was prepared for purchase of the property. Typical construction in the
area consists of one and two story wood frame structures over a basement or crawlspace
with an attached garage. The residence will be located in the building envelope shown on
Figure 1. Basement and garage floors will be slab -on -grade. Cut depths are expected to
range between about 2 to 9 feet. Foundation loadings for this type of construction are
assumed to be relatively light and typical of the proposed type of construction.
If building conditions or foundation loadings are significantly different from those
described above, we should be notified to re-evaluate the recommendations presented in
this report.
Site Conditions: The site is located at the top of a ridgeline along the north and east side
of the Roaring Fork River valley at the edge of a rolling mesa. There was about 21/2 feet
of snow cover at the time of our field exploration. Vegetation consists of sage brush,
grass and weeds in the front part of the lot and a pinon and juniper forest with a ground
cover of grass and weeds in the building area. The ground surface slope in the building
envelope is moderate down to the south.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating three exploratory pits at the approximate locations shown on Figure 1. The
logs of the pits are presented on Figure 2. The subsoils encountered, below about 6
inches of topsoil, consist ofbasalt boulders and cobbles in a sandy silt matrix. Results of
swell -consolidation testing performed on a relatively undisturbed sample of the matrix
r-• 1 1 C'
'nC 421 cc A7 r gi1verrhnrne 970-468-1989
_2 -
der
soils, presented on Figure 3, indicate lavshowed abol�x�collapsepoten�am(settlement
oisture
conditions and light loading. The sample after
under constant load) and moderate compressibility undoeincreased Y gravel (minus (m nus Sting.
Results of a gradation analysis performed on a same n
ch
fraction) obtained from the site are presented on Figure
ig re 4. No free
to moist water was observed in
the pits at the time of excavation and the soils were slightly
Foundation Recommendations: Considering the subsoil Wetrecommend spread tions encountered in thee
exploratory pits and the nature of the proposed construction,
footings placed on the undisturbed natural soils
oisedderesidencesigned r Tan he matrix soallowable ots tend to
il bearing
pressure of 2,500 psf for support of the prop
compress after wetting and there could be some post -construction continuous walls and 2 feet fo settlement.
Footings should be a minimum width of 16 inchesvel
columns. Loose and disturbed soils encountered abeanfoundation
° level extended down to the
withinthe excavation should be removed and the footing g
undisturbed natural soils. Utility line trenches and such as 1exiavang o excavations than about 4 Voids
� created from
et
may require rock excavation techniques
�h uta be backfilled with concrete or a structural
boulder removal at footing gradepercent standard Proctor density at a moisture
material such as road base compacted to 9S adequate cover above
content near optimum. Exterior fongs ould be provided Pla Placement of footings at east 36 inches
their bearing elevations for frost protection.
below the exterior grade is typically used in thiC� area.
lees such astinuous byassum'ngwalls
an
should be reinforced top and bottom to span to
unsupported length of at least 12 feet. Foundation based o�n � qretaining
a emit fluid units
should be designed to resist a lateral earth p
weight of at least 50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil,
of some p suitdiffable
to
support
ovemently,
loaded slab -on -grade construction. To reduce the effects
floor slabs should be separated from all bearingFloorslab
walls s control columns othts should be used to
which allow unrestrained vertical movement.
reduce damage due to shrinkage cracking. The Tbasedon experienceements for joint the intended
cing and slab
reinforcement should be established by the designeravel should be placed beneath
slab use. A minimum 4 inch layer of free -draining gr
basement level slabs to facilitate drainage. This material less thaconsist
2 �sF� ng he N� h
aggregate with less than 50% passing the No. 4 sieve
200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of
maximum standard Proctor density at a moisture content near optimum. Required fill can
consist of the on-site soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: Although free water was not
enc oondwatedrucan develop during exploration,ng our it
has been our experience in the area that local perchedgr
times of heavy precipitation or seasonal runoff. Frozen �cosurunoff
create a perched condition. We recommend below-gradeconstruction. uring spring
asretaining
Tl.. 1nlanr1Q
walls. crawlspace 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 fret leas l foot below g granular lowest d terial. ac adjacent finishe drain be placed at each level of excavation and a
grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular
material used in the underdrain system should contain less than passingoinches. the o. 200 The
sieve, less than 50°o passing the No. 4 sieve and have a mai. s
drain gravel backfill should be at least 1' - feet deep.
Surface Drainage: The following drainage
precautions
residence has been observed during
construction and maintained at all times
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% d to at of the least 90% of the maximum standarmum standard Proctor density d
pavement and slab area
Proctor density in landscape areas. Free -draining wall backfill should be
capped with about 2 feet of the on-site, 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 6 inches in the first 10 feet in unpaved
areas and a minimum slope of 3 inches in the first 10 feet in pavement and
walkway areas. A swale may be needed uphill to direct surface runoff
around the residence.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at
least 10 feet from the building. Consideration should be given to the use
of xeriscape to limit potential wetting of soils below the foundation caused
by irrigation.
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 express 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 Figure 1 and to the depths shown on Figure 2, the proposed type of
construction, and our experience in the area. Our services do not include determining the
presence, prevention or possibility omold °ern d about MOBC, thr other biological en a profnants essional sOBal in
C)
developing in the future. If the client
this special field of practice should be consulted. Our 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 encountered during construction appear different from those described in this
Joh No.106 0179
-4 -
report, we should be notified at once so re-evaluation of the recommendations may b{
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 fill by a representative of the geotechnical
engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Louis E. EIler
Reviewed by:
%7
:!ILHBUriry#
(ORE O Da,' 1C`
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-'� �` 24443 #
Daniel E. Hardin, P.E...44110. ;° ., , P 4
oot
LEE/djblDt1AL tt
attachments Figure 1 - Location of Exploratory Pits
Figure 2 -- Logs of Exploratory Pits
Figure 3 t Swell -Consolidation Test Results
Figure 4 - Gradation Rest Results
cc: Jordan Architecture - Attn: Brad Jordan
Job No.106 0179
APPROXIMATE SCALE
1'60
1
1
LOT 77
r-�
PIT 3
BUILDING
/ ENVELOPE
/ PIT 1 PIT 2
/ ■ •
L
i
LOT 76
FILING 7
BENCH MARK: GROUND AT BUILDING
ENVELOPE CORNER;
ELEV. = 100 0', ASSUMED.
ELK SPRINGS DRIVE
1
1
OPEN
SPACE
106 0179
HEPWORTI+PAWLAK GEOTIECFWICN-
LOCATION OF EXPLORATORY PITS
Figure 1
a)
L
5
10
LEGEND:
.. J
T
PIT 1
ELEV.= 92.1'
PIT 2
ELEV. = 97.7
C=25.2
DD=68
JV +4=34
l j200=46
TOPSOIL; sandy sit and clay, organic, fsrm, moist, dark brown.
PIT 3
ELEV = 98.7'
0
10
BASALT COBBLES AND BOULDERS (GM); in a silty sand maatT�ftc, dense, slightly moist to moist, light brown,
calcareous. J
2' Diameter hand driven liner sample.
Disturbed bulk sample.
Practical digging refusal with backhoe in basalt boulders.
NOTES:
1 _ Exploratory pits were excavated on February 27, 2006 with a Cat 430D backhoe.
2. Locatiors of exploratory pits were measured approximately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory pits were measured by instrument level and refer to the Bench Mark shown on Figure 1.
4. The exp`oratory pit 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 pit logs represent the approximate boundaries between
material types and transitions may be gradual.
6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
VAC = Water Content (%)
DD = Dry Density (pcf)
+4 = Percent retained an the No. 4 sieve
-200 = Percent passing No. 200 sieve
Depth - Feet
I106 0179
HEPWORT*PAWuu[ GEOTECHNICAL
LOGS OF EXPLORATORY PITS
Figure 2
Compression %
0
1
2
3
5
01
Moisture Content = 25.2 percent
Dry Density = 68 pcf
Sample of: Sandy Silt Matrix
From: Pit 2 at 3 Feet
Compression
upon
wetting
1.0
APPLIED PRESSURE - kst
10 100
106 0179
HEPW QRTI+PAWLAK GEOTECHFUCAL
SWELL -CONSOLIDATION TEST RESULTS
Figure 3
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HYDROMETER ANALYSIS
2a F#R 7 HR TIME READINGS U S STANDARD SERIES
0 45 M N 15 MiN 60MiN19M'N 4 MIN 1 MIN 0200 #100 #50 #30 #1+3
S EVE ANALYS :S 1
1 CLEAR SQUARE OPENINGS J
#4 318' 314' 1 1i2' 3' 5` 6" 8° 100
10
20
30
40
50
60
70
SO
90
100
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SW M=1.1
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001 002 005 009 019
037 074 150 300 600 1 18 2 36 4 75 9 512 57 19 a 37 5 76.2 12152 203
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
GRAVEL 34 %
SAND GRAVEL
cInE I COARSE FlhE I MARTA G7BELE5
SAND 20 % < AND CLAY 46 %
LIQUID LIMIT % PLASTICITY INDEX %
SAMPLE OF: Very Silty Sandy Gravel with Cobbles FROM Pit 2 at 2 thru 4 Feet
106 0179 I
Gem
HEPWDRTFFPAWLAK GEOTECHNICAL
GRADATION TEST RESULTS
90
80
70
60
50
40
30
20
10
0
;131:iy31ZkE;E .I'i1Z[r
Figure 4