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' .
HEPWORTH-PAWLAK GEOTECHNICAL
SUBSOIL STUDY
llq't\11 11 h l' l\d 1l 1;,., ... 1, .... ,, 111. i,'~l) I " 11 •1 1: . hi Ii -! I •ll·,111., l ' 11 11·~ I ,1,,11 I "11 '• l°IJ.·111 •1;. q:; ,,,_
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FOR FOUNDATION DESIGN PROPOSED MODULAR HOME
3869 COUNTY ROAD 245 GARFIELD COUNTY, COLORADO
JOB NO. 114 495A
NOVEMBER 28, 2014
PREPARED FOR:
LOIS RYDEN P.O. BOX 1142
COMMERCE CITY, COLORADO 80022
TABLE OF CONTENTS
PURPOSE .AN'D SCOPE OF STUDY ..•••.•......•......•........•• -.. ....... ,.. .••........ ., .•••.•.••• _ .• ., ......• - 1 -
PROPOSED CONSTRUCTION ........................................................... ....................... :- 1 -
SITE CO'NDITIONS ...................... .......... - .............................. - .......•.....••... ············-·····- 2 -
F.IBLD EXPLO'RA.TION ........... .......... .. ................... , __ ................................. _ .......••. ,.. .....• - 2 ..
SlJBSURF ACE CONDITIONS .............................. -........................... ,,,_ ............... _ .. :- 2 -
FOlJNDATION BEARING CONDITIONS ................................................................. - 3 -
DESIGN RECOJIAMENDATIONS ... ..... , ............ ................. .................... .. .. _ .... ........... :- 4 -
SPREAD FOOTIN"GS ·······························-··· ··························-······························'"' 4 -HELICAL PIERS ........................................................................ ...................................... - 5 -FLOOR SLABS ....................... .............................................. ......................... - ..... ,. .. - 6 -'l.JN'DERDRAIN' SYSTEM •.•.•. "' .......... ............ ... _. .•.....•••......••......••.. _ ........... ...... ,,, .... :- 7 -SURFACE DRAIN'AGE ...... , ............ , ............... -...................... _ ...................... ~ ...• , .•...... ':' 7 -
LJl\,flTATIONS ............ ........ ..................... , .... .. .... ........ , .......................................... , ..•..••.•.. - 8 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 through 6 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Job No. 114 495A
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsurface study for a proposed modular home to be
located at 3869 County Road 245, 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 gcotecbnical
engineering services to Lois Ryden, dated October 31, 2014.
A field exploration program consisting of exploratory borings was conducted to obtain
infonnation on subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their compressibility or swell and
other engineering chamc~eristics. 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 this study and presents our conclusions, design recommendations
and other geotechnical engineering considerations based on the proposed construction and
the subsoil conditions encountered.
PROPOSED CONSTRUCTION
The proposed construction includes a modular home to be placed on the site and located
between our exploratory borings generally as shown on Figure 1. The modular home will
have a structural floor over a crawlspace. For the purpose of our analysis, foundation
loadings for the structure were assumed to be relatively light and typical of the proposed
type of construction.
If building loadings, location or grading plans are significantly different from those
described above, we should be notified to r~valuate the recommendations contained in
this report.
Job No. 114 49SA
-2 -
SITE CONDITIONS
At the time of our exploration the building footprint had been cut do~ about 1 to 5 feet
below the existing site grade, which had been previously graded to an unknown extent.
The site is located on a bench cut into a north facing slope roughly as shown on Figure I .
The slope in the area of the proposed build~g is moderate with a steep slope up to the
south about 50 feet south of the proposed building area. An existing residence is located
about 200 feet west of the proposed building area.
F1ELD EXPLORATION
The field exploration for the project was conducted on November 17, 2014. Two
exploratory borings were drilled at the locations shown on Figure 1 to evaluate the
subsurface conditions. The borings were advanced with a 4 inch diameter continuous
flight auger powered by a truck-mounted CME-4SB drill rig. The borings were logged by
a representative of Hepworth-Pawlak Geotechnical, Inc.
Samples of the subsoils were taken with a 2 inch I.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 sub~oils. Depths at which the samples were taken and the penetration
resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples
were returned to our laboratory for review by the project engineer and testing.
SUBSURFACE CONDmONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
Topsoil in the proposed building area had been removed. The subsoils encountered in the
borings consisted of stiff to bard sandy clay with scattered gravel and shale fragments.
Job No. 114 495A
-3 -
The density generally appeared to increase with depth to the full depth of exploration of
45 feel The clay soils can possess an expansion potential when wetted.
Laboratory testing performed on samples obtained during the field exploration included
natural moisture content and density. Swell-consolidation testing was perfonned on
relatively undisturbed drive samples of the clay subsoils. The swell-consolidation test
results, presented on Figures 4 through 6, indicate low compressibility under relatively
light surcharge loading and a low to moderate expansion potential when wetted under a
constant light surcharge. Swell pressures of about 1.5 to 5 ksf were exhibited by the
samples. The laboratory testing is summarized in Table 1. .
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The subsoils encountered at the site are expansive. Shallow foundations placed on
expansive soils like those encountered at this site can experience movement causing
structural distress if the clay is subjected to changes in moisture content.
Spread footings bearing on the natural clay soils, and designed for a minimum dead load
pressure, can be used for foundation support of the building with a risk of movement ·
The risk of movement is primarily if the bearing materials become wetted and precautions
should be taken to prevent wetting.
As an alternative with a low risk of movemen~ a helical pier or "screw pile" foundation
can be used to penetrate the expm;isive materials to place the bottom of the piers in a zone
of relatively stable moisture condition and make it possi'ble to load the piers sufficiently
to resist uplift movements. U~ing a pier foundation, each column can be supported on a
single pier and the building walls are founded on grade beams supported by a series of
piers. Loads applied to the piers are transmitted to the soils at a depth below expected
Job No. 114 49SA
-4-
moisture change primarily through end bearing pressure on the pier helices. In addition
to their ability to reduce differential movements caused by expansive materials, helical
piers can develop moderate load capacity. The piers can be constructed relatively quickly
and should experience a re1atively small amount of movement.
Provided below are recommendations for spread footings with a minimum dead load
pressure and helical piers or "screw piles,, for the building.
DESIGN RECOMMENDATIONS
SPREAD FOOTINGS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, the building can be founded with spread footings
bearing on the native clay soil with a minimum dead load pressure. Footings placed on
the clay subsoils have a risk of foundation movement if the bearing soils experience
changes in moisture content.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed o~ the natural clay site soils should be designed for an
allowable bearing pressure of 2,500 psf with a minimum dead load
pressure of 800 psf. If concentrated loads and grade beams are required to
achieve the minimum dead load pressure, a minimum 4 inch void fonn
should be used below all grade beams to prevent uplift on the grade beams
from soil heave. Based on experience, we expect initial settlement of
footings designed and constructed as discussed in this section will be up to
about 1 inch. Additional movement could occur if the clay bearing soils
become wetted. The magnitude of the additional movement would depend
on the depth and extent of the wetting but may be on the order of 1 inch
for a wetted depth up to about 10 feet.
Job No. 114 495A
-5-
2) The footings should have a minimum width of 16 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 adequate for this area of Garfield County.
4) Continuous foundation walls should be heavily reinforced top and bottom
to span local anomalies and better withstand the effects of some
differential movement such as by assuming an unsupported length of at
least 14 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 60 pcf. An underdrain should be provided
behind retaining walls to prevent build-up of hydrostatic pressures and
wetting of the crawlspace.
5) A representative of the geotecbnical engineer should observe all footing
excavations to evaluate bearing conditions.
HELICAL PIERS
Considering the expansion potential and depth of the clay soils and the nature of the
proposed construction, it should be feasible to found the modular home with a helical pier
or ••screw pile" foundation system that extends down into a stable (non-active) moisture
zone of the clay soils with a low risk of movement Recommendations for helica1 piers or
"screw piles" are presented below.
A helical pier or "screw pile" foundation system is a heavy duty helical piling that has
been used locally to resist heaving due to expansive soils. Helical piers can be installed
by local contractors such as Chris Lake: Great Lakes Construction (970-379-0161) or
Tommie Kane: Flat Top Steel Piering {970-216-5948). We expect the helical piers or
"screw piles" will need to be on the order of 15 to 20 feet long to achieve the desired
anchorage in a zone of stable moisture content, but the pier installation contractor should
be contacted for specific loading and design infonnation. For end bearing in the very stiff
Job No. 114 49SA
-6-
to hard clay soils the piers should develop an allowable load capacity on the order of 20
kips. A representative of the geotechnical engineer should be on site to observe pier
installation. A void form at least 4 inches thick should be provided below grade beams to
prevent uplift of the foundation in the event of subgrade heave. Precautions should be
taken to prevent post-construction wetting of the sub grade soils.
FLOOR SLABS
Floor slabs present a problem where expansive materials are present near floor slab
elevation because sufficient dead load cannot be imposed on them to resist the uplift
pressure generated when the materials are wetted and expand. We recommend that
structural floors with crawlspace below be used for all floors in the building that will be
sensitive to upward movement.
Slab-on-grade construction may be used (such as for a garage, if constructed) provided
the risk of distress is understood by the owner. We recommend placing at least 3 feet of
nonexpansive granular structural fill below floor slabs to help mitigate slab movement
due to expansive soils.
To reduce the effects of some differential movement, nonstructural floor slabs should be
separated from all bearing walls, columns and partition walls with expansion joints which
allow unrestrained vertical movement Interior non-bearing partitions resting on floor
slabs should be provided with a slip joint at the bottom of the wall so that, if the slab
moves, the movement cannot be transmitted to the upper structure. This detail is also
important for wallboards, stairways and door frames. Slip joints which allow at least l ~
inches of vertical movement are recommended. Floor slab control joints should be used
to reduce damage due to shrinkage cracking. Joint spacing and slab reinforcement should
be established by the designer based on experience and the intended slab use.
Required fill beneath slabs should consist of a suitable imported granular material,
excluding topsoil and oversized rocks. The suitability of structural fill materials should
be evaluated by the geotechnical engineer prior to placement. The fill should be spread in
thin horizontal lifts, adjusted to at or above optimum moisture content, and compacted to
lob No. 114 49SA
-7-
95% of the maximum standard Proctor density. All vegetation, topsoil and loose or
disturbed soil should be removed prior to fill placement
The above recommendations will not prevent slab heave if the expansive soils underlying
slabs-on-grade become wet. However, the recommendations will reduce the effects if
slab heave occurs.
UNDERDRAIN SYSTEM
Although groundwater was not encountered during our exploration, it bas been our
experience in the area and where clay soils are present that local perched groundwater
may develop during times of heavy precipitation or seasonal runoff. Frozen ground
during spring runoff can create a perched condition. Therefore, we recommend below
grade construction, such as crawlspace areas, be protected from wetting by an underdrain
system. The drain should also act to prevent buildup of hydrostatic pressures behind
foundation walls.
The underdrain system should consist of a drainpipe surrounded by free-draining granular
material placed at the bottom of the wall backfill. The drain lines should be placed at
each level of excavation and at least 1 foot below lowest adjacent finish grade, and sloped
at a minimum I% grade to a suitable gravity outlet. Free-draining granular material used
in the drain system should consist of minus 2 inch aggregate with less than 50% passing
the No. 4 sieve and l~s than 2% passing the No. 200 sieve. The drain gravel should be at
least 2 feet deep. Void form below the grade beams can act as a conduit for water flow.
An impervious liner such as 20 mil PVC should be placed below the drain gravel in a
trough shape and attached to the grade beam with mastic to keep drain water from
flowing beneath the grade beam and to other areas of the building.
SURF ACE DRAINAGE
The following drainage precautions should be observed during construction and
maintained at all times after the structure has been completed:
Job No. 114 495A
-8-
1) Excessive wetting or drying of the foundation excavations and underslab
areas should be avoided during construction. Drying could increase the
expansion potential of the clay soils.
2) Exterior backfill should be adjusted to near optimum moisture and
compacted to at least 95% of the maximum standard Proctor density in
pavement areas and to at least 90% of the maximum standard Proctor
density in landscape areas. Free-draining wall backfill should be capped
with about 2 feet of the on-site 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 I 0 feet in unpaved
areas and a minimum slope of 3 inches in the first 10 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
S} Landscaping which requires regular heavy irrigation should be located at
least 10 feet from foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally a.ccepted 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 borings drilled at the locations
indicated on Figure 1, the proposed type of construction and our experience in the area.
Our services do not include determining the presence, prevention or possibility of mold or
other biological contaminants (MOBC) developing in the future. If the client is
concerned about MOBC, then a professional in this special field of practice should be
consulted. Our findings include interpolation and extrapolation of the subsurface
conditions identified at the exploratory bol'ing;g and variations in the subsurface
conditions may not become evident until excavation is perfonned. If conditions
Job No. 114 495A
-9-
encountered during construction appear to be 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 not responsible for technical interpretations by others of our infonnation. 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 modi fl.cations of 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.
Sincerely,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
~~~ James A. Parker, P.E., P.G.
Reviewed by:
JAP/ksw
cc: Phil Danielson (i.!rnihil(a juno.\.:om)
SGM - Bill Swigert (bills«rs!!111-i111:.com)
Job No. 114 495A
EXISTING RESIDENCE
0
BORNJG1
APPROXIMATE SCALE 1· = 20'
114 495A
BORING2 0
LEGEND:
• 0
BORING3 0
EXISTING EXCAVATION
• BORING2
BORING DRILLED FOR THIS STUDY.
BORING DRILLED FOR PREVIOUS STUDY BY CHEN·NORTHERN
PAO POSED BUILDING LOCATION
LOCATION OF EXPLORATORY BORINGS Figure 1
BORING 1 o ELEV.= 100'
APPAOX!MATEAOJACEHt' EXCAVATION eonoM
14/12 WC•11.4 00• 99 21/12
5
15112 10 WC•8.6
00• 106
28/12 15
30/12 20
-~ I
.s:; a ~ 33/12
25
31/12 30
56/12 35
40
59/12 45
114 495A
BORING2 ELEV.= 105.5'
APPROXIMATE ADJACENT EXCAVATICH BOTTOM
25112 WC=6.8 00=119
37/12
34/12 WC=6.9 00=123
59/12
0
5
10
15
20
as if • .c
25
a ~
30
35
40
Note: Explanation of symbols Is shown on Figure 3.
45
LOGS OF EXPLORATORY BORINGS Figure 2
LEGEND:
D p
CLAY (CL); silty, sandy, scattered gravel and shale fragments, stiff to hard, slightly moist, brown, row to medium plasticity.
Relatively undisturbed drive sample; 2-lnch 1.0. Callfomla liner sample.
14112 Drive sample blow count; Indicates that 14 blows of a 140 pound hammer falling 30 Inches were required to drive the Calffomla sampler 12 Inches.
NOTES:
1. Exploratory borings were drilled on November 17, 2014 with 4-inch diameter continuous night power auger.
2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan provided.
3. Elevations of exploratory borings were measured by hand level and refer to Boring 1 as 100.
4. The exploratory boring locations and elevations should be considered accurate only to the degree lmplled by the method used.
5. The lines bel\.Veen materials shown on the exploratory boring logs represent the approximate boundaries between material types and transitions may be gradual.
6. No free water was encountered In the borings at the time of drilling. Fluctuation in water level may occur with tlme.
7. laboratory Testing Results: WC = Water Content (%) DD =- Dry Density (pct)
114 495A LEGEND AND NOTES Figure 3
I
Moisture Content = 11.4 percent Dry Density = 99 pcf Sample of: Sandy Clay
I From: Boring 1 at 2 1/2 Feet
I I I I I I I I I I 1
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i T"-H+Ll ~\ I l - I I '* -1 I z I t I/ 1 I I I 0 (i) I I ~ 2 I I I I
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(i) I
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I '
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I 1 I i i I
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I I I ' l 1 l I t '
0.1 1.0 10 100 APPLIED PRESSURE ( ksf)
114 495A ~tech SWELL-CONSOLIDATION TEST RESULTS FIGURE 4 HEPWORTii.PAWLAK GEOTECHN ICAL
I I I ' Moisture Content = 8.6 percent Dry Density = 106 pcf I
i Sample of: Sandy Clay 'Nith Gravel
I From: Boring 1 at 9 Feet
I I I I I I ;
I I I I I I 1 I n I ~ I I
I
I I ~ ~ I 0 I I
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i r I I I I
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! 11 i I I ' 11111 I
' 1111
I I I I I I I 11 I J I I I
0.1 1.0 10 100 APPLIED PRESSURE ( ksf)
114 495A ~tech SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 HEPWO RTH·PAWU<K GEOT£CHNICAL
Moisture Content = 6.8 percent
1 Ory Density = 119 pct Sample of: Sandy Clay with Claystone Pieces From: Boring 2 at 7 Feet - 0
ti. r---- r-- o, __ z f--. i.-. -0 1 '~ Cl)
) ~ z
~ " 2 I
\ ~) z 0 (ij
3 (/) w Expani ~ion a: a.. upo~ :? wetti1 g 0 4 c.:>
5
0.1 1.0 10 100
APPLIED PRESSURE ( ksf)
Moisture Content = 6.9 percent
Dry Density = 123 pcf
Sample of: Sandy Clay with Claystone Pieces From: Boring 2 at 14 Feet
- 1 ti. ---.... - ['1 z
"-0 0 ......... (ij
~ n I ~~
1 • z
Q Cl)
2 (/) w
~ a: a.. ~
8 3 t:Xpan Ion
upo~
wet ti IQ
0.1 1.0 10 100 APPLIED PRESSURE ( ksf)
114495A ~ SWELL-CONSOLIDATION TEST RESULTS FIGURE 6 HEPWORTH.PAWLAK t:U•nn:'.CHNICAL.
HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 Job No. 114 49SA
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL GRAOATJON AmRBERG LIMITS UNCONFINED
MOISTURE NATURAL
GRAVEL SAND PERCENT COMPRESSIVE SOIL OR DRYDENSITV PlASTIC BORING OEPTif CONTENT PASSING NO. LIQUIDUMIT STRENGTH (") l") 200SIEVE
INDEX BEOROCK 1YPE
(ft) '") (Jlc:f) l"I l"l IPSFJ
1 2~ 11.4 99 Sandy clay
9 8.6 106 Sandy Clay with Gravel
2 7 6.8 119 Sandy Clay with Claystone Pieces
14 6.9 123 Sandy Clay with Claystone Pieces