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HEPWORTH-PAWLAK GEOTECHNICAL

SUBSOIL STUDY

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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