HomeMy WebLinkAboutSubsoil Study for Foundation Design 05.12.2021t (+rt [:xr*åinË:rnrqËü
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An Employec Onrncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenrvood@kumarusa.com
www.kumarusa.com
Ofñce Locations: Denver (HQ), Patker; Colorado Springs, Fort Collins, Glenr'vootl Springs, and Sumrnit County, Colorado
May 12,2021
Sam Augustine
625 EastHyman Avenue, #104
Aspen, Colorado 81611
sam. au gu stine(Ðcompass. com
Project No.2I-7-293
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 8, St. Finnbar
Farm, 28 St. Finnbar Farm Road, Garfield County, Colorado
Dear Szun:
As requested, Kurnar & Associates, Inc. performecl a subsoil sfudy for design of foundations at
the subject site. The study was oonducted in accordance with our agreöment for geotechnical
engineering services to you dated March23,202I. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
repod.
Proposed Construction: Plans for the proposed residence have not been deveioped. We
assume the house will be 1 to 2 stories of wood frame construction, located on the site in the area
of Pits I and 2 shown on Figure L Ground floor will be slab-on-grade or structural over a
shallow crawlspace. Cut depths are expected to range between about 2Io 3 feet. Foundation
loadings for this type of construction are assumed to be relatively liglrt 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 was vacant and is relatively flat with a slight slope down to the
southwest toward the Roaring Fork River located south of the building area. Vegetation in the
building area consists of grass and weeds with cottonwood trees sumounding the building site.
The building area elevation is above the 10O-year flood plain and floodway as shown on the site
plan. There is an existing one-story house located on Lot 9 to the southeast of the subject lot.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
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 1 foot of topsoil, consist of I to
2 feet of soft, sand and clay overlying medium dense, slightly silty sandy gravel with cobbles
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down to the bottom of the pits at 6 feet. Ground water was observed in the bottom of the pits at
5%to 6 feet deep. Results of a gradation analysis perf-ormed on a sample of the slightly silty
sandy gravel with cobbles (minus S-inch fraction) obtained from Pit 1 are presented on Figure 3
The soils above the ground water were moist to very 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 undisfurbed natural gravel soil designed for an allowable soil bearing pressure of
3,000 psf for support of the proposed residence. The topsoil and upper clay soils tend to
compress when loaded and should be removed from the building area. Footings should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed
soils encountered at the foundation bearing level within the excavation should be rernoved and
the footing bearing level extended down to the undisturbed natural granular soils. 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 finish 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 fèet. Foundation walls
acting as retaining structures should be designed to resist alaleral earth pressure based on an
equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill.
['loor Slabs: The natural on-site soils, exclusive of topsoil and clay, 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 requirernents for joint spacing and slab reinforcement should be
established by the designer based on experience and the intenclecl slab use. A minimum 4 inch
layer of free-draining grcvel should be placed slabs to facilitate drainage. This rnaterial should
consist of minus 2-inchaggregate with less than 50Yo passing the No. 4 sieve and less than2o/o
passing the No. 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 gravel soils or a suitable impofted gravel devoid of vegetation, topsoil and oversized rock.
Groundwater: Due to the risk of wetting fiom the nearby river and the relatively shallow
ground water associated with it, we recommend that the ground floor of the house be slab-on-
gtade elevated well above the 100-year flood level. Crawlspaces are not recommended due to
Kumar & Associateg, lnc. @ Project No. 2'l-7-293
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the shallow groundwater and risk of wetting in the event of a flood. A perimeter drain system is
not required tbr slab-on-grade ground floor construction elevated above the existing ground
surface.
Surfhce Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during consttuction.
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 and slab areas
and to at least 90o/o of the rnaximum standard Proctor density in landscape areas.
3) The ground surface sunounding the exterior of the building should be sloped to
clrain away from the foundation in all directions. We recommend a minimurn
slope of 6 inches in the f,rrst l0 feet in unpavecl areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas.
4) Roof downspouts and drains should tlischarge well beyond the limits of all
backfì11.
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 I
and to the depths shown on Figure 2, the proposed type of constructiotr, 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 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 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 Proiect evolveso 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 adclitional analysis
Kumar & Associates, lnc. o Project No, 21-7-293
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or modificâtions 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 ñrrther assistance, please let us know.
Respectfully Submitted,
Kumar & Associateso
Daniel E. Hardin,
Rev. by: SLP
DEH/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Kumar & Associates, lnc. @ Project No, 2l'7-293
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APPROXIMATE SCALE-FEEÏ
Fig. 1LOCATION OF TXPLORATORY PITS21 -7 -293 Kumar & Associates
PIT 1 PIT 2
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LEGEND
TOPSOIL: ORGANIC SANDY CLAY, ROOTS. SOFT, MolST, DARK BROWN
cLAy AND SAND (CL-SC): SOFT, MOIST, DARK BROWN.
GRAVEL AND COBBLES (cP): SANDY, SLIGHTLY SILTY, MEÐ|UM DENSE, MOIST TO WET, BROWN
Ir
DISTURBED BULK SAMPLE
9 orprH To wATER LEVEL ENcouNTERED AT THE rtME oF DtGctNc.
--+ DEPTH AT WHICH PIT CAVED WHOLE DIGGING'
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 30, 2021
2. THE EXPLORATORY PITS WERE LOCATED BY THE CLIENT.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTII.
4 THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE
IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIf LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS ENCOUNTERED IN lHE PITS AT THE TIME OF EXCAVAIION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D A22);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM O II¿O);
21 -7 -293 Kumar & Associates LOGS OF EXPLORATORY PITS Fis. 2
SIEVE ANALYSISHYDROMETER ANALYSIS
CHR SAUARE OPENINCg
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IIYE RruING
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2.OIN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 7A % SAND 25 %
LIQUID LIMIT - PLASTICITY INDEX
SAMPLE OF: Sllghtly Silly Sondy Grovel wlfh Cobbles
SILT AND CLAY 5 %
FROM: Plt I O 5' to 6'
Thos€ l€sl resullr opply only lo lhc
sqmpl!! which woro l.rhd, Th.
lasllng rrporl sholl nol br raprgduc.d,
6xc€pl ln full, wllhout tho wrltlen
opprovol of Kumqr & Assoc¡ofsr, lnc.
si€v€ onolyrls l.sl¡ng ls perfo¡ñ.d lnqccordo¡c¡ with ASTM D6915, ASTM D7928,
ÀSlM C136 ond/or ASTM Dll40.
SAND GRAVEL
FINE COARSEFINEMEDTUM ICOARSE
Fis. 3Kumar & Associates GRADATION TEST RESULÏS21 -7 -293