HomeMy WebLinkAboutSoils Report 01.23.20201(+A
Kwnar & Anuslutes, Ina.'
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.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 59, SPRING RIDGE RESERVE
HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-105
JANUARY 23, 2020
PREPARED FOR:
TERRY & HEIDI RUONAVAARA
160 SPRINGRDIGE DRIVE
GLENWOOD SPRINGS, COLORADO 81601
thruonavaara@ .msn.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
GEOLOGY -2-
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS ... - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 20-7.105
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
59, 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 the
foundation design. The study was conducted in general accordance with our agreement for
geotechnical engineering services to Terry and Heidi Ruonavaara dated January 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 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
At the time of our study, design plans for the residence were conceptual. The building is
proposed in the area shown on Figure 1. We assume excavation for the building will have a
maximum cut depth of one level, about 10 feet below the existing ground surface. For the
purpose of our analysis, foundation loadings for the structure were assumed to be relatively light
and typical of the proposed type of construction.
If building location, grading or loading information differ significantly, we should be notified to
re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The site was vacant and covered with about 6 inches of snow at the time of our field exploration.
The site is located below a hillside and is moderately sloping down to the west, gradually
becoming steep in the upper portion of the lot. The ground surface was vegetated with sage
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brush and grass in the lower part and junipers in the upper part of the lot. Red sandstone bedrock
outcrops are visible to the northeast of the building envelope. Single-family residences and
Hidden Valley Drive are to the west and south and vacant land is to the north and east.
GEOLOGY
According to the Geologic Map of the Leadville 1 °x 2° Quadrangle, Northwestern Colorado, by
Tweto, Ogden, Moench, R.H., and Reed, J.C., dated 1978, the site is underlain by Maroon
Formation and Weber Sandstone covered by thin colluvium. The Maroon Formation is
described as maroon and grayish -red sandstone, conglomerate, and mudstone of the Permian and
Pennsylvanian periods. Weber Sandstone is described as yellow -gray sandstone of the Permian
and Pennsylvanian periods.
FIELD EXPLORATION
The field exploration for the project was conducted on January 10 and 17, 2020. Three
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 augers powered
by a truck -mounted CME -45B 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 and hardness of the bedrock. 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, below up to about 1/2 foot of topsoil, consist of about 1 to 101/2 feet of medium
dense/stiff to very stiff sand and silt with gravel underlain by very hard sandstone/siltstone
bedrock.
Kumar & Associates, Inc. ® Project No. 204.105
on the natural soils or bedrock or a minimum of 2 feet of structural fill in soil areas to reduce the
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Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell -consolidation
testing performed on relatively undisturbed drive samples of the silt soils, presented on Figure 4,
indicate low to moderate compressibility under conditions of loading and wetting.
No free water was encountered in the borings at the time of drilling and the subsoils and bedrock
were slightly moist.
FOUNDATION BEARING CONDITIONS
The natural sand and silt soils possess a low bearing capacity and a low to moderate risk of
settlement. The bedrock possesses moderate to high bearing capacity and a low risk of
settlement. It is likely that the footings would span both soil and bedrock materials if footing
elevations are relatively shallow.
Lightly loaded spread footings bearing on the sand and silt
soils and bedrock will have a low to moderate risk of excessive differential settlement. The risk
of differential settlement is due to the variable bearing conditions, especially at the transition
from natural soils to bedrock and if the soils were to become wetted. To reduce the risk of
differential settlement, spread footings could bear entirely on the underlying bedrock or on a
minimum of 2 feet of structural fill. The contractor should be prepared to remove shallow
bedrock by splitting, ram hoe excavation, blasting, or other rock excavation methods.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
risk of settlement.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the natural soils, bedrock or a minimum of 2 feet of properly
compacted structural fill should be designed for an allowable bearing pressure of
1,500 psf. Footings placed entirely on bedrock should be designed for an
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allowable bearing pressure of 4,000 psf. Structural fill should be compacted to a
minimum of 98% of the standard Proctor density. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this section
will be about 1 inch or less. Additional settlement up to about 1 inch could occur
if the natural soils are wetted depending on the depth of wetted soil.
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
offoundations at least 36 inches below exterior grade is typically used in this
area.
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 natural soils or bedrock. Soils exposed in
footing areas should then be moistened and compacted to a minimum of 95% of
the standard Proctor density. Structural fill can consist of the onsite soils
excluding organics and rock larger than 6 inches and should extend to at least one
foot beyond footing edges.
6) A representative of the geotechnical engineer should observe 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
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of at least 40 pcf for backfill consisting of the on-site soils. 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.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95% 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 0.40. 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 95% 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
separated from all bearing walls and columns with expansion joints which allow unrestrained
Kumar & Associates, Inc. ® Project No. 20-7.105
6
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 basement level slabs to facilitate drainage. This
material should consist of minus 2 -inch aggregate with at least 50% 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 least 95% 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.
IJNDERDRAIN 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
recommend below -grade construction, such as retaining walls, crawlspace and basement 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 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to
a suitable gravity outlet. 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 1Y2 feet deep. Where
footings are placed on soils outside of bedrock areas, an impervious membrane such as 30 mil
PVC should underlie the drain gravel in a trough shape and attach to the foundation wall with
mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
Kumar & Associates, Inc. Project No. 20-7-105
7
1) Inundation 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 95% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% 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
3 inches in the first 10 feet in paved areas. Free -draining wall backfill 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 should be located at least
5 feet from foundation walls. Consideration should be given to the use of
xeriscape to limit potential wetting of soils below the foundation 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 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 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 so
that re-evaluation of the recommendations may be made.
Kumar & Associates, Inc. Project No. 20.7-105
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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 verify 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.
Respectfully Submitted,
Kumar & Associates, Inc.
Steven L. Pawn
Reviewed by:
a
9.RE.949 91114
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Daniel E. Hardin, P.
SLP/kac
Kumar & Associates, Inc. Project No. 20.7-105
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PROPOSED
RESIDENCE
LOT 59
BORING 3
°Ink
Flag
0
LOT 58
5 0 30
APPROXIMATE SCALE -FEET
20-7-105
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
BORING 1
EL. 6422.5'
BORING 2
EL. 6419'
BORING 3
EL. 6415'
6425 6425
• 6420
6415
18/12
WC=4.2
DD=104
fJ 10/12
WC=5.0
DD=120
-200=56
w' 150/1
w-
o- 6410"
w
J
W
50/0
— 6405
6400
1
50/3
50/0
50/5
R.. R:i
6420
6415
30/12
WC=5.4 1-
DD=107 w
- I
20/12 6410 —
a
w
J
W
18/12
WC=5.7
DD=108
-200=56
-j 30/4, 10/0
6405
6400
6395 6395 —I
20-7-105
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
TOPSOIL; SLIGHTLY CLAYEY SAND AND SILT, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN.
SAND AND SILT (SM—ML); MEDIUM DENSE/STIFF TO VERY STIFF, SLIGHTLY MOIST, RED.
SANDSTONE/SILTSTONE BEDROCK, VERY HARD, SLIGHTLY MOIST, RED. MAROON FORMATION.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
18/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 18 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
t PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 10 AND 17, 2020 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 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 (pcf) (ASTM 02216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140);
20-7-105
Kumar & Associates
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
1
0
—1
— 2
— 3
— 4
— 5
1
0
— 2
SAMPLE OF: Very Sandy Silt with Gravel
FROM: Boring 1 ® 2.5'
WC = 4.2 %, DD = 104 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPUED PRESSURE — KSF 10 100
P1... 1..1 Wte a •'k' 10 w
�.a 1..id. 10. 019 noon
ihetl nm h.ke wilcd�.ce.>,t 0,
*NILW +.7f1nu1 u...du... n P1.1aI m
I emer snd 4.nol01n, 10e. S.O.
ee..9detlen t.rO* a..d m
la.nr
xce dwr. n40 a ss�s
SAMPLE OF: Very Sandy Silt with Gravel
FROM: Boring 3 ® 2.5'
WC = 5.4 %. DD = 107 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE — KSF 10 100
20-7-105
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
I(+A
Kumar & Associates, inc. e
Geotechnical and Matecia(s Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Proiect No. 20-7-105
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY(%)
(pcf)
GRADATION
PERCENT
PASSING200 G NO.
VE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH SOIL TYPE
(Psf)
BORING
DEPTH
(ft)
GRAVEL
SAND
(%)
1PLASTIC
LIQUID LIMIT
(%)
INDEX
(%)
1
21/2
4.2
104
Very Sandy Silt with
Gravel
5
5.0
120
56
Very Sandy Silt with
Gravel
3
2YY
5.4
107
Very Sandy Silt with
Gravel
10
5.7
108
56
Very Sandy Silt with
Gravel