HomeMy WebLinkAboutSubsoils Report for Foundation DesignI (1A Hlffi fi#,}1:i$f*'""ld
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An Employcc Orncd Gompony
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 Q{Q), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STT]DY
FOR FOUI\DATION DESIGN
PROPOSED RESIDENCE
LOT F13, ASPEN GLEN SUBDIVISION
191 MOUNTAIN MEADOW ROAI)
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-570
ocToBER ll,20l9
REVTSED JULY 14,2020
PREPARED FOR:
DAVID WOOD
38632 N. DONOVAN COURT
ANTHEM, ARTZONA 85086
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TABLE OF'CONTENTS
PURPOSE AND SCOPE OF STI]DY
PROPOSED CONSTRUCTION
SITE CONDITIONS..........
SUBSIDENCE POTENTIAL
FIELD E)PLORATION
SUBSURFACE CONDITIONS ..
DESIGN RECOMMENDATIONS ...............
FOUNDATIONS
FOLINDATION AND RETAINING WALLS
FLOOR SLABS
IINDERDRAIN SYSTEM
SURFACE DRAINAGE
LrMITATIONS...............
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - GRADATION TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 1$7.570
PTJRPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot F13, Aspen Glen Subdivision, l9l Mountain Meadow Road, Garfield County, Colorado.
The project site is shown on Figure l. The purpose of the study was to develop
recommendations for the foundation design. We understand that this report will be considered in
the purchase/sale of the property. The study was conducted in accordance with our agreement
for geotechnical engineering services to David Wood dated September 23,2019.
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 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 CONSTRUCTION
The proposed residence will be a one and two-story structure with an attached garage. Ground
floor will be structural over crawlspace with slab-on-grade in the garage. Grading for the
structure is assumed to be relatively minor with cut depths between about 3 to 5 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 site was vacant at the time of our site visit on September25,2019. The lot slopes gently
down to the south and is vegetated with grass and weeds. There is a low berm along the north
property line bordering the golf course. An active irrigation ditch parallels the west property
line.
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SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits
associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the
gypsum under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, several sinkholes were observed
scattered throughout the Aspen Glen Development. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the Roaring Fork Valley.
Sinkholes were not observed in the immediate area ofthe subject lot. The nearest mapped
sinkhole is located about 500 feet north of the property. The lot is located outside the broad
subsidence area mapped about 200 feet southwest of the lot. No evidence of cavities was
encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot Fl3 throughout the service life of the proposed residence, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
development. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
FIELD EXPLORATION
The field exploration for the pruject was conducted on September 25, 2Al9- Two exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurfacc conditions.
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, Inc.
Samples of the subsoils were taken with a l%-inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 140 pound hamrner falling 30 inches. This
test is similar to the standard penetration test desmibed by ASTM Method D-1.586. The
penetration resistance values are an indication of the relative density of the subsoils. Depths at
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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 ofthe subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about r/zfootof topsoil overlying relatively dense, silty sandy gravel with
cobbles and possible boulders. Drilling in the dense granular soils with auger equipment was
difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit at
about 1l feetdeep inbothborings.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus lYz-inchfraction) ofthe coarse granular subsoils are shown on Figure 3.
No free water was encountered in the borings at the time of drilling.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurf;ace conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,000 psf. Based on experience, we expect
settlement of footings O".ign"Offiiffit"d as discussed in this section will
be about I inch or less.
2) The footings should have a minimum width of 16 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
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of foundations at least 36 inches below exterior grade is typically used in this
area.
4) Continuous foundation walls should be reinforced top ancl bottom to span local
anomalies such as by assuming an unsupported lcngth of at least 10 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) All existing topsoil and any loose or disturbed soils should be removed and the
footing bearing level extended down to the relatively dense natural granular soils.
The exposed soils in footing area should then be moistened and compacted.
6) A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining strucftires rvhich are laterally supported and can be expectcd 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 weiglrt of at least 45 pcf for backfill consisting
of the on-site granular 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 35 pcf for backfill consisting of the on-site granular soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as ad.iacent 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.
Backfill should be placed in uniform lifts and compacted to at least 90Yo of themaximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95%o of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
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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. Backfill should not contain organics, debris or rock larger
than about 6 inches.
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 0.50. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 375 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 a granular material compacted to at least
95Yo of themaximum 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
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 beneath slabs. This material should consist of minus 2-inch
aggregate with at least 50olo retained on the No. 4 sieve and less than 2% 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. Required fill can consist of the on-
site granular soils devoid of vegetation, topsoil and oversized rock.
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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 also create a perched condition. We
recommend below-grade construction, such as retaining walls and crawlspace areas, be protected
from wetting and hydrostatic pressure buildup by an underdrain system.
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 l%oto
a suitable gravity outlet, sump and pump or drywell. Free-draining granular material used in the
underdrain system should contain less than 2% 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 lVz feet deep.
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% of the maximum standard Proctor density in pavement and slab arcas
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 6 inches in the first i0 feet in unpavcd areas and a minimum slope of 2/z
inches in the first l{J t'eet in paved areas. Free-draining wall backfill should be
capped with about 2 feet of the on-site soils to reduce surfacc water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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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 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 veri$'that the recommendations
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.
Respectfu lly Submitted,
Kumar & Associateso Inc.
Daniel E. Hardin, P.E.
Reviewed by:
Steven L. Pawlak, P.E
DEH/kac
Kumar & Associates, lnc. o Prcjec{ No. 19-7'570
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BORING 2
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APPROXIMATE SCALE_FEET
1 9-7-570 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1
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BORING 2
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LEGEND
TOPSOIL; ORGANIC SILTY SAND WITH GRAVEL, SOFT, MOIST, DARK BROWN.
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GRAVEL (CU); SlHOy, SILTY, WITH COBBLES AND POSSIBLE BOULDERS, DENSE TO VERY
DENSE, SLIGHTLY MOIST, LIGHT BROWN.
i DRTVE sAMpLE, 1 s/'-tNcH l.D. SPLIT SPooN STANDARD PENETRATION TEST
=^T^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 50 BLOWS OF A 140-POUND HAMMER
'"/' FALLTNG SO TNCHES WERE REQUIRED TO DRIVE THE SAMPLER 6 INCHES.
f rnlcrrcAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 25, 2019 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 MEASURED BY HAND LEVEL AND REFER
TO THE GROUND SURFACE AT BORING 1 AS ELEVATION 1OO.O FEET.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS 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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU OOSIS);
-200= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl14O)-
WC=2.1
+4=50
-200=1 9
19-7 -570 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fig. 2
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DIAMETER OF
CLAY TO SILT COBBLES
GRAVEL 50 r
LIQUID LIMIT
SAMPLE OF:
SAND 31 %
PLASTICITY INDEX
SILT AND CLAY 19 %
FROM: Boring 1 O 5' & lO' (Combin6d)
Thoce lotl relulls opply only lo lhs
aomplos whlch rero lest6d. Thglosllng rgport shqll nol b6 rcproducld,excepi ln full, vllhout the v.ittefr
opprcYol ot Kumor & Asociolos, lnc.Slw. qnqly3ls lrsllng ls prrfom.d ln
9999rd9nc. wllh_ASIlt D6915, ASTM D7928,Aslll C136 ond/or ASTM Dltito.
I]YDROMETER ANALYSIS SIEVE ANALYSIS
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SAND GRAVEL
FINE MEDIUM COARSE FINE COARSE
19-7 -570 Kumar & Associates GRADATION TEST RESULTS Fig. 5