HomeMy WebLinkAboutSubsoils Study for Foundation Designl(|n Hiffiiilrffi$ffn'"'n;*"
An Employcc Owncd Compony
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
SCANNED
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 6, BLOCK 5, BATTLEMENT CREEK VILLAGE
461 MEADOW CREEK DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 23-7-540
NOVEMBER 13,2023
PREPARED FOR:
ROGER WALTERS
87 HOGAN CIRCLE
BATTLEMENT MESA, COLORADO 81635
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ...............- I -
PROPOSED CONSTRUCTION I
SITE CONDITIONS I
FIELD EXPLORATION 1
SUBSURFACE CONDITIONS .,
'L-
DESIGN RECOMMENDATIONS ....- 2 -
FOUNDATIONS
FOLINDATION AND RETAINING WALLS..
FLOOR SLABS
UNDERDRAIN SYSTEM ...................
SURFACE DRArNAGE.......................
LIMITATIONS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 _ LEGEND AND NOTES
FIGURES 4 & 5 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
2
J
4
4
5
.-6-
FIGURE I - LOCATION OF EXPLORATORY BORINGS
Kumar & Associates, lnc. o Project No.23-7-540
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot6, Block 5, Battlement Creek Village, 461 Meadow Creek Drive, Garfield County, Colorado.
The project site is shown on Figure 1. The purpose of the study was to develop recommendations
for the foundation design. The study was conducted in accordance with our agreement for
geotechnical engineering services to Roger Walters dated September 8,2023.
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 recofirmendations 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 CONSTRUCTION
The proposed residence will be a one-story, wood frame structure with attached garage. Ground
floors will be structural over crawlspace for the living areas and slab-on-grade for the garage.
Grading for the structure is assumed to be relatively minor with cut depths between about 3 to
6 feet. 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 subject site was vacant at the time of our field exploration. The ground surface is gently to
moderately sloping generally down to the north-northwest. Vegetation consists of grass and
weeds with some sage-brush.
FIELD EXPLORATION
The field exploration for the project was conducted on October I8,2023. 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 augers powered by a truck-
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Kumar & Associates, lnc, o Projec't No.23-7-540
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Samples of the subsoils were taken with l% -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-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 returned 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 one foot of topsoil, consist of very stiff sandy, clayey silt
down to about 8 feet underlain by medium dense/hard, silty sand and clay to depths of about
15 to 19 feet overlying dense, silty, clayey gravel with basalt rocks down to the maximum
explored depths of about 16 to 20 feet. Drilling in the underlying coarse granular soils was
difficult due to the cobbles and boulders and practical auger drilling refusal was encountered in
the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand grain size gradation analyses. Results of swell-
consolidation testing performed on relatively undisturbed drive samples of the sandy silt soils,
presented on Figures 4 and 5, indicate low compressibility under existing moisture conditions
and amoderate to high collapse potential when wetted under a constant light surcharge. The
laboratory testing is summarizedinTable 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the 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 sandy silt soils should be designed
for an allowable bearing pressure of 1,000 psf. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this section
will be less than 1 inch. Additional differential settlement up to around I to
2 inches could occur depending on the depth and extent of future wetting and
Kumar & Associates, Inc, @ Project No.23-7-540
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precautions should be taken to keep the bearing soils dry. The footing grade
exposed in the excavation should be evaluated for and the need
for sub-excavation and of the soils with
. An alternative with a risk is to on
@rng sand and clay soils encountered below a depth ofabout 8 feet.
2)The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
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
area.
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.
The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural soils. The exposed soils in
3)
footing area should then be moistened and compacted.
6) A representative ofthe geotechnical engmeer o all footing
excavations prior to concrete placement to evaluate bearing conditions.
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 50 pcf for backfill consisting
of the on-site 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 40 pcf for backfill consisting of the on-site soils.
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.
4)
s)
Kumar & Associates, lnc. @ Projec{ No.23-7-540
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Backfill should be placed in uniform lifts and compacted to at least 90o/o of the maxlmum
standard Proctor density at a moisture content near optimum. 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 use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 330 pcf. The
coefficient of friction and passive pressure values recommended 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 95o/o of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade
construction with a risk of settlement mainly if the bearing soils are wetted. 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 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 base course should be placed beneath the
garage slab for support. This material should consist of minus 2-inch aggregate with at least
50Yo retained on the No. 4 sieve and less than l2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95oh of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. We
Kumar & Associates, lnc. o Project No.23-7-540
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recommend below-grade construction, such as retaining walls and basement areas, be protected
from wetting and hydrostatic prsssure buildup by an underdrain system. An underdrain should
not be provided around the crawlspace to help protect the bearing soils against wetting.
Where provided, the drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free-draining granular material. The drain should be
placed at each level of excavation and at least I foot below lowest adjacent finish grade and
sloped at a minimum lo/o to a suitable gravity outlet or sump and pump. Free-draining granular
material used in the underdrain system should contain less than 2%o passing the No. 200 sieve,
less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel
backfill should be at least I%feet deep. An impervious membrane such as 20 mil PVC should
be placed beneath the drain gravel in a trough shape and attached to the foundation wall with
mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting
future settlement and building distress. 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 backhll 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 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
slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of
2Y, inches in the first 1 0 feet in paved areas. Free-draining wall backfill, if any,
should be covered with filter fabric and capped with about 2 feet of the on-site,
finer graded, soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation such as sod and sprinkler
heads 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 inigation.
Kumar & Associates, lnc. @ Project No.23-7-540
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LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this areaat 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 ourexperience 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 exhapolation 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 recofilmendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recornmendations 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,
Kumar & Associates, Inc.
David A. Noteboom, Staff Engineer
Reviewed By:
Steven L. Pawlak,
SLPlkac
Kumar & Associates, lnc. o Projec{ No.23-7-540
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23-7 -540 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2
0 0
2e/ 12 34/ 12
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WC=4.5
DD=88
15/12
WC=5.0
DD=92
-200=81
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Fig. 223-7-540 Kumar & Associates LOGS OF EXPLORATORY BORIGNS
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LEGEND
N
TOPSOIL; SANDY CLAYEY SILT WITH ROOTS AND ORGANICS, FIRM, DRY TO
SLIGHTLY MOIST, LIGHT BROWN.
SILT (ML); CLAYEY, SLIGHTLY SANDY TO SANDY, VERY STIFF, TAN TO LIGHT BROWN, TRACE
TO SLIGHTLY CALCAREOUS.
SAND AND CLAY
SLIGHTLY MOIST,
(sc-cL), stLTy, GRAVELLY W|TH BASALT PtECES, MEDTUM DENSE/HARD,
WHITE AND GRAY, HEAVILY CALCAREOUS.
GRAVEL (OU); SINOY, SILTY WITH BASALT ROCKS TO PROBABLE BOULDER SIZE, DENSE,
SLIGHTLY MOIST, WHITE AND GRAY, HEAVILY CALCAREOUS.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
i DRIVE SAMPLE, 1 S/9-|NCH l.D. SPLIT SPOON STANDARD PENETRATION TEST.
6A t1^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 29 BLOWS OF A 140-P0UND HAMMERzr/ tz FALLTNG Jo TNcHES wERE REQUIRED To DRtvE THE sAMpLER 12 tNcHES.
I enlcrrcnL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 18, 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 DENSITY (PCt) (ISTV D2216);
-2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM Dl140)
23-7 -540 Kumar & Associates LEGEND AND NOTES Fig. 3
SAMPLE OF: Sondy Silt
FROM:Boringl@4'
WC = 4.5 %, DD = 88 pcf
ft@ s4 dur oppy onry b ur
hmd6 tartad. lh. tGting ruport
rholl not b! ruprcduc.d, cx6pt ln
Iull, r'(4loul th. rdtt n opprcwl of(ufrdr ond Aalclotd. lnc, Sw.ll
conelldotlon tctlng pcrfomcd ln
occordoncr rith Aslu D-4546,
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
2
0
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3-rooaz.oo -12
-14
-16
-18
1.0 APPLIED PRESSURE - KSF t0
SWELL-CONSOLIDATION TEST RESULTS Fig. 423-7 -540 Kumar & Associates
SAMPLE OF: Sond ond Cloy
FROM:Boring2@9'
WC = 7.0 %, DD = 106 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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1.0 APPLIED PRESSURE - KSF 10
Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 523-7-540
I(tA l(unw & Associates, lnc.@
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23-7-540
soll oR
BEDROCK TYPE
Sandy Silt
Sandy Clay
Sandy Silt
Sand and Clay
PSFI
UNCONFINED
COMPRESSIVE
STRENGTH
(ol
PLASTIC
INDEX
ATTERBERG LIMITS
(o/ol
LIQUID LIMIT
PERCENT
PASSING NO.
200 stEVE
78
I8
SAND
(vt
GRADATION
c/t
GRAVEL
(ocf)
NATURAL
DRY
DENSITY
88
110
92
106
(%l
NATURAL
MOISTURE
CONTENT
4.5
7.8
5.0
7.0
CATION
(ft.)
DEPTH
4
9
4
9
SAMPLE LI
BORING
1
2
