HomeMy WebLinkAboutSubsoils Report for Foundation Designrcrf iiçlfl#ir:trtrn$Ëü**'
An Employse Owned Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
wwwkumarusa.com
Office Locations: Denvø (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
June L6,2023
Jim Mindling
32 Buffonball Lane
Weston, Connecticut 06883
mindlins@gtnail.com
Project No.23-7-274
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 7 , St. Finnbar
Farm, 30 St. Finnbar Farm Road, Garflreld County, Colorado
Gentlemen:
As requested, Kumar & Associateso Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our proposal for geotechnical
engineering services to Jim Mindling dated May 2,2023. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Plans for the proposed residence were in progress at the time of our
study. The residence will generally be a 1 to 2 story wood-frame structure with a detached
single-story ADU located on the site as shown on Figure 1. Ground floors could be slab-on-grade
or structural over a shallow crawlspace. Cut depths are expected to range between about 2 to
3 feet. Foundation loadings for this type of construction are assumed to be relatively light and
typical ofthe proposed type of construction.
If building conditions or foundation loadings are significantly different from those described
aboveo we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The site is vacant and relatively flat with a slight slope down to the north.
Blue Creek is located north of the building area and the Roaring Fork River borders the west side
of the lot. Vegetation in the building area consists of grass and weeds with cottonwood trees to
the north and west of the building site. The building area elevation is above the 1O0-year flood
plain and floodway as shown on the site plan.
Subsurface Conditions: The subsurface conditions at the site were evaluated by drilling four
exploratory borings at the approximate locations shown on Figure l. The logs of the borings are
presented on Figure 2. The subsoils encountered, below about2 to 3% of topsoil, consist of
denseo slightly silty sandy gravel and cobbles with probable boulders down to the boring depths
of 6% to l0 feet where practical auger drilling refusal was encountered. Results of gradation
-2-
analyses perfbrmed on small diameter drive samples of the sandy gravel (minus l%-inch
fraction) are presented on Figure 4. The laboratory test results are summarized in Table 1.
Ground water was encountered in the borings at depths of 4% to 5 feet. The soils above the
ground water were moist to very moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory borings and the nature of the proposed construotion, we recommend spread footings
placed on the undisturbed natural gravel soil designed for an allowable soil bearing pressure of
WtheproposedresidencenndADU.Footingsshouldbeaminimumwidth
of 16 inches for continuous walls and2 feet for columns. The topsoil and loose and disturbed
soils encountered at the foundation bearing level within the excavation should be removed and
the footing bearing level extended down to the undisturbed natural granular soils. 'We should
observe the completed excavation for bearing conditions. 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 feet. Foundation walls acting as retaining
structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit
weight of at least 50 pcf for the on-site granular soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. To reduce the effects of some differential movemen! 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 requirements for joint spacing and slab reinforcement should be
established by the designer based on experience and the intended slab use. A minimum 4-inch
layer of free-draining gravel should be placed below slabs to facilitate drainage. This material
should consist of minus 2-inch aggregate with less than 50%o passing the No. 4 sieve and less
than2%o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95Vo of maximum
standard Proctor density at a moisture content near optimum. Rcquircd fill can consist of the
orsite gravel soils or a suitable irnported gravel devoid of vegetation, topsoil and oversized rock.
We recommend vapor retarders conform to at least the minimum requirements of ASTM E1745
Class C material. Ceftain floor types are more sensitive to water vapor transmission than others.
For floor slabs bearing on angular gravel or whore flooring system sonsitivo to water vapor
transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum
Kumar & Associates, lnc. @ Project No. 23-7-274
a-J-
requirements of ASTM 81745 Class A material. The vapor retarder should be installed in
accordance with the manufacturers' recommendations and ASTM 81643.
Groundwater: Due to the risk of wetting from the relatively shallow groundwater and potential
rise to near flood level, we recommend the ground floor of the buildings be slab-on-grade
elevated to well above the 100-year flood level. Crawlspaces are not recommended due to the
shallow groundwater and risk of wetting in the event of a flood. A perimeter drain system is not
required for slab-on-grade ground floor construction elevated above the existing ground surface.
Surface 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 construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90o/o 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 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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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 borings drilled at the locations indicated on Figure I
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 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 borings 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.
Kumar & Associates, lnc. @ Project No. 23-7-274
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This report has been prepared for the exclusive use by our client for design purpos€s. We me not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field sen¡ic€s during consüuction to review and
monitor the implementation of our recommendations, and to verify that the recommendations
have beeir oppropriately interpreted. Significant desig changcs may require additionul analysis
or modifications to the recomme,ndations prese,lrted herein. We recommend on-site obsen¡ation
of excavations and foundation bearing stata 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,
Kumar & Associates, lnc.
Steven L. Pawlak, P
Rev. by: DEH
SLP/kac
Attachments: Figure I - Location of Exploratory Borings
Figure 2 - Logs of Exploratory Borings
Figure 3 - Legend and Notes
Figure 4 - Graóation Test Results
Table I - Summary of Laboratory Test Results
Cc: KA Designworks * Erik Hendrix (ed(@designworks.coq)
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Kumar & Associates, lnc. e Project No. 23-7-274
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APPROXIMATE SCALE-FEET
23-7 -27 4 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1
EL. 6258'
BORING 2
EL. 6258'
BORING 5
EL. 6259'
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6259'EL.
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17/12
23/6, 50/5
WC=9.3
-200=8
22/6, 40/6
WC=9.1
+4=57
-200=9
3s/6, so/5
WC=27.9
DD=93
-2OO=50 F
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5 18/6, 53/6
+4=50
-200=9
50/s 22/12 515/6, 50/5
10 10
23-7 -27 4 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
TOPSOIL; ORGANIC SILTY SAND TO SANDY SILT, FIRM, MOIST, BROWN
GRAVEL AND COBBLES
WITH DEPTH, BROWN,
(GM-GP);
ROUNDED
SLIGHTLY SILTY, SANDY, BOULDERS, DENSE, MOIST TO WET
ROCK.
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DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRTVE SAMPLE, 1 5/8-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST.
A,'^ DRIVE SAMPLE BLOW COUNT' INDICATES THAT 17 BLOWS OF A 14o_POUND HAMMER
"/ '' FALLTNG 30 TNCHES WERE REQU|RED To DRtvE THE SAMPLER t2 tNcHES.
-=- DEPTH T0 WATER LEVEL ENCOUNTERED AT THE TIME OF DRILLING
---> DEPTH AT WHICH BORING CAVED.
I PRACTICAL AUGER REFUSAL.
NOTES
1 THE EXPLORATORY BORINGS WERE DRILLED ON MAY 3, 2023 WITH A 4_INCH DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATIONS 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
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCf) (ASTU D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06913);
-2OO = PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140).
23-7 -27 4 Kumar & Associates LEGEND AND NOTES Fig. 3
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HYDROMEfER ANALYSIS SIEVE ANALYSIS
TilaE RE^O|NOS
t4 His t His
U.S, STANDARD SEiIES CLEAR SOUARÊ OPEr{lr.tOS
af^' lfla 1 1/r' 3,
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+7 ---r
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------+
+----7
---1--f-___r_l_++
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_____+
-
1
t'
SAND GRAVEL
rT--r-
FINE MEDIUM COARSE FINE COARSE
2û
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100
so
l0
70
t0
50
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50
20
to
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to
20
30
40
50
GO
70
ao
to
fo0
¡
.t I.125 t,
CLAY TO SILT COBBLES
GRAVEL 50 X SAND 11
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sondy Groval
%
PLASTICITY INDEX
SILT AND CLAY 9 %
FRCIM:Boringlos'
2
a
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100
90
60
70
60
30
ao
50
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10
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to
20
30
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50
60
70
a0
90
foo
,
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IN MILLIMETERS
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DIAMETER OF
CLAY TO SILT
SAND
COBBLES
MEDIUM FINE
GRAVEL 57 X SAND
LIQUID LIMIT
SAMPLE OF: Slìghlly Silly Sondy Oravel
34X
PLASTICITY INDEX
SILT ANO CLAY 9 X
FROM:8oring3O2.5'
Th.¡r lltl rc.ull' qpply oñly lo lh.
romplol whlch v.r. l.¡i.d. Th.l.¡llng r.porÌ lholl not b. r.p.oduc.d,.xc.pf ln lull, wllhoul lh. wrltl.n
opprovql ol Kumdr & A¡roclol.r, lnc,
Sl!v. onolyll¡ l.rllng lt p.rfom.d ln
occordonc. ylth ASTY D5913, ASIM D7928,
ASlt¡ Cí36 ond/or ASÌl¡ Dll,10.
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIÍE RüDIXOS
14 HRS 7 HnS tt
U,S. S NOARD SERIES CLSAR SOUARE OPENIÑGS
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-
GRAVEL
COARSEFINE
23-7 -27 4 Kumar & Associates GRADATION TEST RESULTS Fis. 4
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TABLE I
SUMMARY OF LABORATORY TEST RESULTS
GPÂnÀflôll ÀT LIHITSSATPTLOCATIOT{
SOIL TYPEBORII¡G
tffi
DEPTH
tol'ì
NATURAL
TOISTURË
coiltENT
NATURAL
DRY
DENSIIY
¿b¿{l
GRAVEL
{%}
SAI{D
(%)
PERCEIIT
PASSI{G t{0.
200 stEvÉ
LIQUID LITIT
l%!
PLASTIC
INDEX
f%l fD!fl
UiICONFINED
cotPREsslvË
STRENGTH
9 Slightly Siþ Sandy GravelI5504t
8 Slightly Silty Sandy Gravel22%9.3
Slightly Silty Sandy GravelJ2Y29.1 57 34 9
Organic Very Sandy Silt42v,27.9 93 50
23-7-274