HomeMy WebLinkAboutSubsoil StudyI(t'T:r
Kumar & Assoclatos' lnG. 5020 County Road 154
Gsotechnicaland Materlals Englneers Glenwood Springs, CO 81601
and Envtronmontalsclenflsts phonä: (970) 945-7ggg
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employec Owncd compony wr¡vr,v.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 64, SPRING RIDGE RESER\rE
HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-684
DECEMBER?2,2020
PREPARED FOR:
MATT JURMU
620 NORTH TRAYER TRAIL
GLENWOOD SPRTNGS, COLORADO 81601
matt@ i anckilaconstruction.com
TABLE OF CONTENTS
PI.IRPOSE AND SCOPE OF STI'DY
PROPOSED CONSTRUCTION
SITE CONDITIONS
GEOLOGY
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOLTNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS ........
FOUNDATIONS
FOTINDATION AND RETAINING WALLS..
FLOOR SLABS...
UNDERDRAIN SYSTEM ...................
SITRFACE DRArNAGE.......................
LIMITATIONS..
FIGI.]RE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGI.IRE 3 - LEGEND AND NOTES
FIGLIRES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Aseociates, lnc.Project No 20-7-684
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot 64, Spring Ridge Reserve, Hidden Valley Drive, Garfield County, Colorado. The project
site is shown on Figure 1. The purpose of the study was to develop recommendations for
foundation design. The study was conducted in accordance with our agreement for geotechnical
engineering services to Matt Jurmu, dated November 6,2020.
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 analyzed to develop rocommendations for foundation fypes, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conclusions, recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will be located in the upper, east part of the building envelope shown on
Figure l. Ground floors could be structural above crawlspace or slab-on-grade. We assume
excavation for the building will be cut about 2 to 8 feet below the existing ground surface.
Foundation loadings for the structure were assumed to be relatively light and fypical of the
proposed type of construction.
If building loadings, location or grading plans are significantly different from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The property was vacant andpartly covered with snow atthe time of our field exploration. The
site is vegetated with grass, weeds and sage brush. The ground surface slopes gently down to the
northwest with around 3 feet of elevation difference in the general building area. Maroon
Formation sandstone is exposed on the hillside to the east of the lot.
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GEOLOGY
According to the Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado, by
Krikham, Steufert, Hemborg, and Stelling, dated 2014, the site is underlain by alluvium and
oolluvium deposits of the Holocene age overlying Maroon Formation.
FIELD EXPLORATION
The field exploration for the project was conducted on November l0 and December 2,2020.
Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the
subsurface conditions. The borings were advanced with 4-inch diameter continuous flight auger
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. spoon sampler. The sampler was driven
into the subsurface materials 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.
SUBST]RFACE CONDITIONS
Graphic logs of the subsurface profiles encountered at the site are shown on Figure 2. Below
about Yz foot of organic topsoil, the subsoils consist of about 4 to 9 feet of loose to medium
dense, silty sand underlain by medium dense/very stiff sand and clay soil. At Boring 1, dense
silty sandy gravelwas encountered below the sand and clay soil at a depth of about 38% feet.
taboratory testing performed on samples obtained during the field exploration included natural
moisture content and density and finer than sand size gradation analyses. Swell-consolidation
testing performed on relatively undisturbed drive samples of the soils, presented on Figures 4
and 5, generally indicate low compressibility under relatively light surcharge loading and
variable compression or expansion potential when wetted under a constant light surcharge. The
laboratory testing is summarizedtn Table 1.
No free water was encountered in the borings at time of drilling and the subsoils were slightly
moist to moist with depth.
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FOUNDATION BEARING CONDITIONS
The subsoils encountered at the site possess variable low to moderate movement potential mainly
when wetted. The expansion potential measured in the clay sample from Boring 2 at 5 feet deep
appears to be an anomaly and the expansion potential should be further evaluated at the time of
excavation. Sub-excavation to 3 feet below footing bearing level and placement of structural fill
could be used to help mitigate movement potential. Surface runoff, landscape irrigation, and
utility leakage are possible sources of water which could cause wetting. Footings placed on the
natural soils can be used for foundation support with the accepted risk of movement. Deep
foundations, such as drilled piers or micro-piles, can be used if the risk of movement cannot be
tolerated. We should be contacted if deep frrundation recommendations are desired.
DESIGN RECOMMENDATIONS
FOLTNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the residence can be founded with spread footings placed on the
undisturbed natural soils with a risk of movement mainly if the bearing soils are wetted.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils can be designed for an allowable
bearing pressure of!00_grfl-Based on experience, we expect initial settlement
of footings designed and constructed as discussed in this section will be up to
about I inch. Additional movement could be around I to lYz inches depending on
the depth and extent of wetting.
2)Thefootingsshou1dhavea@forcontinuousfootings
and 24 inches for isolated{rads.
3) Continuous foundation walls should be heavily reinforced top and bottom to span
local anomalies and limit the risk of differential movement. One method of
analysis is to design the foundation wall to span an unsupported length of at least
12 fe:et. Foundation walls acting as retaining structures should also be designed to
resist alateral earth pressure as discussed in the "Foundation and Retaining
Walls" section of this report.
Kumar & Associates, lnc.Project No 20-7-684
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4)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 the exterior grade is typically used in this
s)
area.
The topsoil and loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural soils.
FOLINDATION AND RETAINING WALLS
Foundation walls and retaining structures which arelaterally 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 fluicl unit weight of at least 50 pcf for backfill oonsisting
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 adjacenÍ" footings, traffrc, construetion materials and equipment. The
pressures recommended above assume drained conditions behind the walls and ahorizontal
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 the maximum
standard Proctor density at near optimum moisture content. 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
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
6)of the geotechnical engineer
excavations prior to concrete placement to evaluate bearing conditions.
representatrve observe all footing
Kumar & Associates, lnc,Project No 20-7.684
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the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.40. 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 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 95Yo 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. There could be differential settlement potential from wetting of the bearing soils
similar to that described above for footings. 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 A-inch layer of relatively well graded sand and gravel such as road base should
be placed beneath slabs constru cted at-grade for support. This material should consist of minus
2-inchaggregate with at least 50olo,retained on the No. 4 sieve and less than I2%opassingthe
No. 200 sieve. A minimum 4-inch layer of free draining gravel with less than2%o passing the
No 200 sieve should underlie basement slabs for drainage.
All fill materials for support of floor slabs should be compacted to at least95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil and oversized þlus 6-inch) rock.
LINDERDRAIN SYSTEM
Although gtoundwater was not encountered during our exploration, it has been our experience in
the arcaand where clay soils are present that local perched groundwater can develop during
times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a
perched condition. Therefore, we recommend below-grade construction, such as crawlspace and
basement areas (if provided), be protected from wetting by an underdrain system. The drain
should also act to prevent buildup of hydrostatic pressures behind foundation walls.
Kumar & Associates, lnc.Project No 20-7-684
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The underdrain system should consist of a drainpipe surrounded by free-draining granular
material placed at the bottom of the wall backfill. The drain lines should be placed at each level
of excavation and at least I foot below lowest adjacent finish grade, and sloped at a minirnum
lo/o grade to a suitable gravity outlet. Free-draining granular material used in the drain system
should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4 sieve and less
than2o/o passing the No. 200 sieve. The drain gravel should be at least llz feet deep. An
impervious liner such as 20 mil PVC should be placed below the drain gravel in a trough shape
and attached to the foundation wall with mastic to keep drain water from flowing beneath the
wall and to other areas of the building.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to prevent wetting of the bearing
soils and limiting building settlement and distress. The following drainage precautions should be
observed during construction and maintained at all times after the residence has been completed:
1) Excessive wetting or drying of the 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 95Yo of the maximum standard Proctor density in pavement areas and to at
leastg}Yo 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. Vy'e recommend a minimum
slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least 10
feet from foundation walls. Consideration should be given to use of xeriscape to
prevent wetting of bearing soils from landscape irrigation.
LIlWITATIONS
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
Kumar & Aseoclates, lnc.Prgject No 20.7.684
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from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
constmction and our experience in the area. Our services do not include døermining the
presence, prevention orpossibility 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 subzurface
conditions may not become evident until excavation is performed, If conditions encountered
during construction appear to be 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 project evolves, we
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to veriff that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications of the recommendations presented herein. W'e recommend on-site observation
of excavations and foundation bearing strata and testing of structural filIby a representative of
the geotechnical engineer.
Respectfu lly Submitted,
Kumar & Associates, Inc.
Steven L. Pawlak, P.
Reviewed by:
F
Daniel E. Haidin, P.E,
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Kumar & Associates, lnc.Project No 20-7-684
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20-7 -684 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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20-7-684 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fig. 2
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TOPSOIL; ORGANIC SILT AND SAND, FIRM, MOIST, DARK BROWN.
SAND (SM); SILTY, LOOSE TO MEDIUM DENSE, SLIGHTLY MOIST, RED-BROWN
SAND AND CLAY
MOIST TO MOIST
(SC-CL); SILTY, SCATTERED GRAVEL, MEDIUM DENSE/VERY STIFF, SLIGHTLY
WITH DEPTH, RED-BROWN.
F::-Àt7flw
GRAVEL (CV); Sllry, SANDY, DENSE, SI-IGHTLY Mo|ST, RED.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
^ Z"^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 9 BLOWS OF A 'I4O-POUND HAMMER
"/ '' FALLTNG so TNCHES wERE REQUIRED To DRtvE THE SAMPLER t2 lNcHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON NOVEMBER 10 AND DECEMBER 2,2O2O 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 AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE TINES 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 ÏHE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM Ð2216);
DD = DRY DENSITY (pcf) (ASTM D2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM Dl 1 40)
20-7 -684 Kumar & Associates LTGEND AND NOTES Fig. 3
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SAMPLE OF: Very Sondy Silty Cloy
FROM:Boringl@20'
WC = 8,4 %, DD = 109 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANÏ PRESSURE
DUE TO WETTING
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SAMPLE OF: Sondy Cloy
FROM:Boring2@5'
WC = 7.8 %, DD = 117 pcÍ
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SWELL_CONSOLIDATION TEST RESULTS Fig.520-7 -684 Kumar & Associates
lcrtKuma & Àssoeiales, lne.€Geotechnical and lllaterials Engineersand Environmenbl ScientisbTABLE 1SUMMARY OF LABORATORY TEST RESULTS1BORING2520I052%(fr)DEPTHSAMPLE LOCATION159.41.88.47.95.44.0(%lNATURALMOISTURECONÏENTr0498100(pcflNATURALDRYDENSITYtt2It7109$tGRAVEL(%)SANDGRADATIONPERCENTPASSING NO.200 srEVE6419t%lLIQUID LIMITMIPLASTICINDEXATTERBERG LIMITSSandy ClayVery Sandy Silty ClaySandy Silty ClaySilty SandSilty SandVery Sandy Silty ClaySOIL TYPEUNCONFINEDCOMPRESSIVESTRENGTHNo.20'7-684