HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.21.23rcrf f;ffi,ffi:rffinl$--"
An Employoa Ornsd Compsny
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Offrce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Sumnit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 2,RALZ SOUTH MrNOR SUBDTVISION
COUNTY ROAD 331
GARFIELD COUNTY, COLORADO
PROJECT NO.22-7-736
FEBRUARY 21,2023
PREPARED FOR:
TITO RUIZ
353 WEST ORCHARD AVENUE
srLT, coLoRADO 81652
titoshandymanservice@yahoo.com
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
FIELD EXPLORATION..
SUBSURI'ACE CONDITIONS ...
FOI.INDATION BEARING CONDITIONS ..
DESIGN RECOMMENDATIONS
FOUNDATIONS
FOUNDATION AND RETAINING WALLS..
FLOOR SLABS
UNDERDRAIN SYSTEM .............
SURT'ACE DRAINAGE.................
LIMITATIONS..
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
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Kumar & Associates, lnc. @ Project No. 22-7-736
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located onLot 2,
Ruiz South Minor Subdivision, County Road 331, south of Silt, Garfield County, Colorado. The
project site is shown on Figure 1. The purpose of the study was to develop reconmendations for
the foundation design. The study was conducted in accordance with our agreement for
geotechnical engineering services to Tito Ruiz dated November 26,2022.
A field exploration program consisting of exploratory borings was conducted to obtain
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, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRTTCTION
The residence will be a two-story wood-framed structure with an attached garage located on the
lot as shown on Figure 1. Ground floors will be structural above crawlspace for the living areas
and slab-on-grade for the garage. Grading for the structure is expected to be relatively minor
with cut depths between about 2%to 4 feet. An auxiliary dwelling unit (ADU) may be built in
the future to the southeast of the proposed residence in the vicinity of our Boring 3, see Figure 1.
We assume relatively light foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The proposed building site was vacant at the time of our field exploration. There was a chicken
coop located in the north-east corner of the lot. The ground surface in the building area is
relatively flat, slopes gently down to the north, and was vegetated with grasses and weeds.
About 3 inches of snow covered the ground at the time of our field exploration.
FIELD EXPLORATION
The field exploration for the project was conducted on January 5,2023. Three exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions
Kumar & Associates, lnc. @ Project No.22-7-736
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Borings 1 and 2 were drilled at the proposed main residence and Boring 3 was drilled at the
future ADU site, and located as directed by the client. The borings were advanced with 4-inch
diameter continuous flight augers powered by a truck-mounted CME-458 drill rig. The borings
were logged by a representative of Kumar & Associates.
Samples of the subsoils were taken with a 2-inch I.D. California liner 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
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 retumed to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils encountered, below about %foot of organic topsoil, consisted of medium stiff to stiff,
sandy to very sandy silt and clay that extended down to the depths drilled at Borings 2 and3 of
21 feet. At Boring 1, relatively dense coarse granular soils were encountered below the silt and
clay soils from 20 feet to the depth drilled of 2l feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density, percent finer than sand-size gradation analyses, and unconfined compressive
strength. Results of swell-consolidation testing performed on relatively undisturbed drive
samples, presented on Figures 4 through 6, indicated generally moderate compressibility under
conditions of loading and wetting. Two of the samples, Borings I @ 5' and Boring 3 @2.5',
showed a low to moderate collapse potential when wetted under a constant 1,000 psf surcharge.
The other sample, Boring 2 @ 5', showed a minor expansion potential when wetted under a
constant 1,000 psf surcharge. The unconfined compressive strength testing indicated medium
stiff consistency for the moist to very moist silt and clay. The laboratory testing is summarized
in Table l.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist to occasionally very moist.
FOUNDATION BEARING CONDITIONS
The upper silt and clay soils are generally stiff and should be suitable for support of lightly
loaded spread footings with some risk of settlement, mainly if the bearing soils are wetted. The
minor expansion potential encountered in one of the samples can be neglected in the foundation
Kumar & Associates, lnc. o Project No. 22-7-736
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(and floor slab) design. A lower risk foundation would be to extend the foundation bearing
down to the underlying dense coarse granular soils such as with helical piers.
Provided below are recommendations for spread footings bearing on the natural soils. If
recommendations for helical piers are desired, we should be contacted.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we believe the buildings can be founded with spread footings bearing
on the natural soils with some risk of settlement. Precautions should be taken to prevent wetting
of the bearing soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,500 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. There could be some post-construction settlement up to
around I inch if the bearing soils were to become wetted, depending on the depth
and extent of the wetting.
2) The footings should have a minimum width of 18 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 used in this
atea.
4) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 14 feet.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the undisturbed firm natural soils. The exposed
6)A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & Associates, lnc. @ Project No. 22-7-736
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FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site fine-grained soils. Cantilevered retaining structures which are separate from the
residence and can be expected to deflect sufficiently to mobilize the full active earth pressure
condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 45 pcf for backfill consisting of the on-site fine-grained soils. The
backfill should not contain organics, debris or rock larger than about 6 inches.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls as needed.
Backfill should be placed in uniform lifts and compacted to at least 90oh of the maximum
standard Proctor density atnear optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or uss large equipment near the wall, since
this could cause excessive lateral pressure on the wall.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.30. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of friction and passive pressure values recornmended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95Yo of the
maximum standard Proctor density at a moisture content near optimum.
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 movement, floor slabs should be
Kumar & Associates, lnc. @ Project No,22-7-736
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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 relatively
well graded sand and gravel, such ast/o-inch base course, should be placed beneath interior slabs
for subgrade support. This material should consist of minus 2-inch aggregate with at least 50%
retained on the No. 4 sieve and less than l2Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fiIl can consist of the
on-site soils devoid of topsoil and oversized (plus 6-inch) rocks.
PEzuMETER DRAIN SYSTEM
It is our understanding the proposed finished floor elevation at the lowest level is at or above the
surrounding grade. A perimeter foundation drain system should not be needed for the proposed
shallow (less than 4 feet deep) crawlspace construction.
It has been our experience in the arcathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a
perched condition. We recommend below-grade construction, such as basement areas,
crawlspace areas deeper than 4 feet, and retaining walls, be protected from wetting and
hydrostatic pressure buildup by a perimeter foundation drain system.
SURFACE DRAINAGE
Positive surface drainage is a very important aspect of the project to prevent wetting of the
bearing soils. 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 and during the life of the structure.
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 90Yo 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
4)
3 inches in the first 10 feet in paved areas.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Kumar & Associates, lnc. @ Project No. 22-7-736
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s)Landscaping which requires regular heavy irrigation, such as sod, and sprinkler
heads should be located at least 5 feet &om 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 area at this time. We make no waranty either express or implied.
The conciusions 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 concemed 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 so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design pu{poses. We are not
responsible for technical interpretations by others of our information. 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 verifu that the recoilrmendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications 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.
Respectfully Submitted,
Kaas"ru*e" & A*seefefes, Xm*'
t\&
David A. Noteboom, Staff Engineer
Reviewed by:
David A. Young,
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LOT 1
LOT 2
Ruiz Sauth Minor Subdiuision
Reception No,
1O.275t Acres
2O.0' Iiigotioft Ditch E*etuefr
Reception No, 785066
,r..r'BORING
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BORING 5
30' Vy'itness Cofrer
*5 Rebdr and
i-1/2' Atutuilue cap
Stan&"d "PLS 36572 WC 3Q'
N 89"45'13',E 546.A0'
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APPROXIMATE SCALE-FEET
50 0
LOCATION OF TXPLORATORY BORINGS Fig. 122-7 -736 Kumar & Associates
BORING 1 BORING 2 BORING 5
0 0
7/12
17/12
WC=7.8
DD=97
-200=53
6/ 12
WC=7,7
DD=98
5 5
5/ 12
WC=12.9
DD=110
11/12
WC=1 1.0
DD=113
s/ 12
WC=21.0
DD= 1 00
10 10
Flrl
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6/ 12
WC=21.4
DD= 1 02
-200=88
UC= 1 ,1 00
6/ 12
WC=13.9
DD= 1 03
-2OO=72
4/12 F
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15 15s/ 12 1o/ 12 8/12
tNC=17.2
DD= 1 07
UC=1,300
20 206/6, 27/6 6/ 12 7/12
25 25
LOGS OF EXPLORATORY BORINGS Fig. 222-7 -736 Kumar & Associates
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LEGEND
N
TOPSOIL; ORGANIC SANDY SILT LOAM, FIRM, FROZEN, SLIGHTLY MOIST, BROWN.
SILT AND CLAY (CL-ML); SANDY TO VERY SANDY, MEDIUM STIFF T0 STIFF, SLIGHTLY MOIST
TO MOIST TO OCCASIONALLY VERY MOIST, BROWN.
GRAVEL AND COBBLES (GM-GC); SANDY, SILTY, CLAYEY, DENSE, MOIST, BRoWN, PRIMARILY
SUBROUNDED ROCKS.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
- Z"^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 7 BLOWS OF A 14o-POUND HAMMER
'/ '' FALLTNG go TNcHES wERE REeUIRED To DRtvE THE sAMPLER t2 tNcHES.
---> DEPTH AT WHICH BORING CAVED IMMEDIATELY FOLLOWING DRILLING.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 5, 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.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF
THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
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 WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216):
DD = DRY DENS|TY (pcf) (nSrV 0ZZt 0);
-2OO = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM DllAO);
UC = UNCONFINED COMPRESSIVE STRENGTH (PSt) (ASTU D 2166).
Fig. 322-7-736 Kumar & Associates LEGEND AND NOTES
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SAMPLE OF: Sondy Sill ond Cloy
FROM: Boring 1 GD 5'
WC = 12.9 %, DD = 1 10 pcf
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(
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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somdd td{rd. Ihc t.ting ropoil
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Conelidotion tdtlng p.rfom.d in
occoddnc. wil ASIII D-4546.
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PRESSURE - KSF 10 100I1.0
SWELL-CONSOLIDATION TEST RESULTS Fig. 422-7 -736 Kumar & Associates
SAMPLE OF: Sondy Silt ond Cloy
FROM:Boring2@5'
WC = 11.O %, DD = 115 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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SWELL_CONSOLIDATION TEST RESULTS Fig. 522-7 -736 Kumar & Associates
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SAMPLE OF: Very Sondy Silt ond Cloy
FROM:BoringS@2.5'
\NC = 7.7 %, DD = 98 pcf
(
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1
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1.0 APPLIED PRESSURE - KSF 10 r00I
Fig. 6Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS22-7 -736
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No. 22-7-736
Sandy Silt and Clay
Sandy Silt and Clay
SOIL TYPE
1,300
Very Sandy Silt and Clay
Sandy Silt and Clay
Sandy Silt and Clay
Very Sandy Silt and Clay
Very Sandy Silt and Clay
Sandy Silt and Clay
(osfl
UNCONFINED
COMPRESSIVE
STRENGTH
110t2.9
001,1
lo/ol
PLASTIC
INDEX
ATTERBERG LIMITS
(%l
LIQUID LIMlT
PERCENT
PASSING NO.
200 stEVE
88
53
72
SAND
(%)
GRADATION
GMVEL
(vt
103
98
100
t07
(pcfl
NATURAL
DRY
DENSITY
102
97
ll3
21.4
7.8
11.0
13.9
7.7
2r.0
t7.2
(o/ol
NATURAL
MOISTURE
CONTENT
(ft)
DEPTN
5
01
2%
5
0I
nl/L/2
5
5I
SAMPLE LOCATION
BORING
1
2
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