HomeMy WebLinkAboutSubsoil Studyrcn Kumar & Associates, lnc,'
Geotechnical and Materials Engineers
and Environmental Scientists
An Employcc Ovrncd Compqny
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
'RECEIVED
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GARFIELD CÜJ"' i'¡
cbtltuuHtrv DEV ELoPiiriËnlI
SUBSOIL STT'DY
FORFOUNDATION DESIGN
PROPOSED SHOP/RESIDENCE
MUSTAI\IG MESA TRAIL
LOT 3, HIGHLTNE RANCH SUBDTVISTON
GARFIELD COTTNTY, COLORADO
PROJECT NO. 22-7-113
MARCH 2,2022
PREPARED FOR:
TARA & DENMS BOOTH
P.O. BOX 4338
GYPSUM, COLORADO 81637
tarakavbooth L4@email.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STTIDY ................ 1 -
PROPOSED CONSTRUCTION 1
SITE CONDITIONS 1
FIELD EXPLORATION ........- 2 -
SIJB SURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM ..............
SURFACE DRAINAGE
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF ÐGLORATORY BORINGS
FIGURE 3 . LEGEND AND NOTES
FIGURE 4. SWELL-CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLE T- SUMMARY OF LABORATORY TEST RESULTS
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3
J
4
4
5
5
Kumar & Associates, lnc, @ Project No. 22-7-113
PT]RPOSE AIID SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed shop/residence to be located at
Lot 3, Highline Ranch Subdivision, Mustang Mesa Trail, 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 Tara & Dennis Booth, dated January 12,2022.
A field exploration program consisting of exploratory borings was conducted to obøin
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 analyzedto 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, recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed shop/residence will be a tall one-story, steel frame, metal skin building with a
portion of the building being a two story residence. The ground floor will be slab-on-grade. The
building is proposed in the area roughly between the exploratory boring locations shown on
Figure 1. We assume excavation for the building will have a maximum cut depth of about 2 to
4 feetbelow the existing ground surface. For the purpose of our analysis, foundation loadings
for the structure were assumed to be relatively light to moderate and typical of the proposed type
of construction.
If building loadings, location or grading plans are significantly different from those described
abeve, we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The site is currently occupied by a 10' by 20',2-story barn,2 storage cont¿iners and a trailer.
There was I to lYz feet of snow covering the site. The snoril had been plowed off the proposed
building area. Vegetation under the snow appeared to consist of grass and weeds. The site
grading appeared natural with a gentle slope down to the north-northwest.
Kumar & Assoclates, lnc, o Project No. 22-7-113
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T,TELD EXPLORATION
The field exploration for the project was conducted on February I,2022. Two exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
The borings were advanced with 4 inch diameter continuous flight auger powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates,Inc.
Samples of the subsoils were taken withl% inch and 2 inch I.D. spoon samplers. The samplers
were 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-l586
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. 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.
SUBSTJRFACE CONDITIONS
Graphic logs of the subsurface profiles encountered at the site are shown on Figure 2. Below
about 1 foot of organic topsoil, the subsoils consist of about 6 feet of very stiff to hard, sandy,
siþ clay overþing 4 to 4 Yz feet of dense gravelly sand and silt. At a depth of about I 1 to
!|Yz feet,the subsoils became dense, very silty sand and gravel with cobbles. Drilling refusal
was encountered in the dense gravel soils at a depth of 13 feet in Boring 2.
Laboratory testing performed on samples obtained during the field exploration included natural
moisture content, density and grain size analyses. Swell-consolidation testing was performed on
relatively undisturbed drive samples of the clay subsoils. The swell-consolidation test results,
presented on Figure 4, indicate low compressibility under relatively light surcharge loading and a
low to moderate expansion potential when wetted under a constant light surcharge. Results of
gradation analyses performed on the minus llz -inch fraction of the sand and gravel subsoils are
presented on Figure 5. The laboratory testing is summarizedin Table l.
No free water \ilas encountered in the borings at time of drilling. The subsoils were slightly
moist to moist.
FOUNDATION BEARING CONDITIONS
The shallow clay subsoils encountered at the site possess low to moderate expansion potential
when wetted. The expansion potential can probably be mitigated by load concentration to reduce
Kumar & Associates, lnc, o Project No.22-7-113
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or prevent swelling in the event of wetting below the foundation bearing level. Surface runoff,
landscape irrigation, and utility leakage are possible sources of water which could crìuse wetting.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions oncountered in the exploratory borings and the nature of
the proposed construction, we recommend the shop/residence be founded with spread footings
placed on the undisturbed natural soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural clay soils can be designed for an
allowable bearing pressure of 2,500 psf. The footings should also be designed for
a minimum dead load pressure of 800 psf. In order to satisff the minimum dead
load pressure under lightly loaded areas, it may be necessary to concentrate loads
by using a grade beam and pad system. Wall-on-grade construction is not
recommended at this site to achieve the minimum dead load.
2) Based on experience, we expect initial settlement of footings designed and
constructed as discussed in this section will be up to about 1 inch. There could be
additional movement of around Vzto I inch if the bearing soils were to become
wet.
3) The footings should have a minimum width of 16 inches for continuous footings
and24 inches for isolated pads.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies and limit the risk of differential movement. One method of analysis is
to design the foundation wall to span an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure of 55 pcf for the on-stie soils used as backfill.
5) 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 the exterior grade is typically used in this
alea.
6) Prior to the footing construction, any existing fill, topsoil and loose or disturbed
soils should be removed and the footing bearing level extended down to
competent bearing soils.
Kumar & Associates, lnc. @ Project No.22-7.113
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A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The on-site soils possess an expansion potential and slab heave could occur if the subgrade soils
were to become wet. Slab-on-gtade construction may be used provided precautions are taken to
limit potential movement and the risk of distress to the building is accepted by the owner. A
positive way to reduce the risk of slab movement, which is commonly used in the area, is to
construct strucfi¡rally supported floors over crawlspace.
To reduce the effects of some differential movemento nonstructural floor slabs should be
separated from all bearing walls and columns 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 will allow at least l%-inches of vertical movement are
recommended. Floor slab control joints should be used to reduce damage due to shrinkage
cracking. Slab reinforcement and control joints should be established by the designerbased on
experience and the intended slab use.
A minimum 4 inch layer of 3/a-inch road base gravel should be placed immediately beneath slabs-
on-grade. This material should consist of minus 1á-inch aggregate with less than50%o passing
the No. 4 sieve and less thart I2Yo passing the No. 200 sieve.
Required fill beneath slabs can consist of imported gravel soils, excluding topsoil and oversized
rocks. The filI should be spread in thin horizontal lifts, adjusted to at or above optimum moisture
content, and compacted to at least 95Yo 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. All plumbing lines should be pressure tested before backfilling to help reduce the
potential for wetting.
UNDERDRAIN SYSTEM
An underdrain system should not be needed for the proposed slab-on-grade first floor
construction.
7)
Kumar & Associates, Inc. @ Project No.22-7113
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SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the shop/residence has been completed:
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 95o/o of the maximum standard Proctor density in pavement 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 12 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first l0 feet in paved areas.
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
5 feet from foundation walls. Consideration should be given to use of xeriscape
to reduce the potential for wetting of soils below the building caused by irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this arca atthis 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 futgre. 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 borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions 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 information. As the project evolves, we
Kumar & Associates, lnc. @ Project No.22-7-1f3
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should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to veriry that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications 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.
Respectfully Submitted,
Ke¡rue*r & Assq¡aåætes, ñ¡ae"
Daniel E. Hardin, P.E.
Reviewed by:
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Steven L. Pawlak, P.E.
DEH/kac
Cc: J. Caliber Construction - Jose Gonzales (it ccfdqal iþtts-tægç1-,s:tçåiçl¡r cgie)
Kugæar & Åsgcl*iaÈ**, l**. 'Fr*j*eå ,àda:r . 'å2-7 -11'"3
APPROXIMATE SCALE_FEET
22-7-113 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1
EL. 101.5'
BORING 2
EL. 100'
0 0
2s/12
WC=8.1
DD=1 04
UC=5,000
21 /12
WC=8.9
DD=99
UC=2,500
5 5
36/ 12
WC=8.7
DD=l 06
-200=88
50/12
WC=9.7
DD=1 05
-200=89
10 46/6, 50/4
WC=14.9
DD=88
-2O0=49
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WC= 15.4
DD=99
-2QO=57
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15 15
50/6
20 2040/6, 50/s
WC=7.8
+4=19
-2OO=37
25 25
22-7 -1 13 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fig. 2
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TOPSOIL: ORGANIC SANDY SILTY CLAY WITH GRAVEL, FIRM, MOISÏ' BROWN.
CLAY (CL): SILTY SANDY, VERY STIFF To HARD, SLIGHTLY MOIST' LIGHT BROWN.
SAND AND S|LT (SM-ML): GRAVELLY, DENSE, SLIGHTLY MOIST, LIGHT BROWN.
SAND AND GRAVEL (SM-GM): VERY SILTY, WITH COBBLES, DENSE' LIGHT BROWN.
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DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMPLE, 1 S/Û-INCH l.D. SPLTT SPOON STANDARD PENETRATION TEST
^Ê,.ı DRIVE SAMPLE BLOW COUNT. INDICATES THAT 25 BLOWS OF A 140-POUND HAMMER¿"/ t ¿' FALLTNG 30 TNCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
f enacrrcAL AUcER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON FEBRUARY 1, 2022 WITH A 4-INCH-DIAMEÏER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PAC]NG
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO THE GROUND AT BORING 2 AS ELEVATION 1OO" ASSUMED.
4. THE EXPLORATORY BORING LOCATIONS AND ETEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROX]MATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
wc = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCt) (ISTU D2216):
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913)¡
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140).
22-7-113 Kumar & Associates LEGEND AND NOTTS Fig. 3
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SAMPLE OF: Sllghtly Sondy Silty Cloy
FROM:Boringf@2.5'
WC = 8.1 %, ùD = 104 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
be
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SAMPLE OF: Slightly Sondy Silty Cloy
FROM:Boring2f9-2.5'
WC = 8.9 %, DD = 99 pcf
EXPANSION UNDER CONSTANT
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22-7-113 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
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SIEVE ANALYSISHYDROMÉTER ANALYSIS
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COBBLES
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GRAVEL 19 ,( SAND
LIQUID LIMIT
SAMPLE OF: Sllty Grqvelly Sond
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PLASTICIW INDEX
SILT AND CLAY 37 %
FROI{:BoringtO20'
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COARSEFINECOARSEMEDIUMFINE
Fig. 5GRADATION TEST RESULTSKumar & Associates22-7-113
l(+rt*iffiif;',i:ifffi*[isü.."'TABLE 1SUIIIMARY OF LABORATORY TEST RESULTSSlightly Sandy Silty ClaySlightly Sandy Siþ ClayVery Siþ Gravelly SandSlightly Sandy Silty ClayVery Sandy SiltSilty Gravelly SandSOILWPEEXPAI{SIONSlightly Sandy Siþ Clay1.01.82,500losflEXPANSIONPRESSURE5,000lolrlPLASTIC[{I,EX{%ìL¡QUID LilIffATTERBERG L¡MITS89495737PÊRCENTPASSTNG ilO.200 stEvE44f,6lSAND91VrlGRAVELGRAIIATI'N8899r0310410699locflTIATURALDRYDENSITY8.99.714.9II8.7t5.47.8fololNATURALrrolsTuRECONTEIIT2%5012tA50120ffitDÊPTH2SAIIPLEBORINGINo.22-7-113