HomeMy WebLinkAboutSoils Report 10.03.2019KFA
Kumar &Is8uok m. ®
Geotechnical and Materials Engineers 5020 County Road 154
and Environmental Scientists G ierIWOOd Springs, CO 81601
phime: (970) 945--7988
fax: (97(0 945-8454
naii kagien WO 0 o marusa,coln
An Employee Owned Company www.kumarilsa.com
Office Locations: Denver (HQ), Parker, Colorado Spzingg, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT S6, FILING 8, ASPEN GLEN
SADDLEBACK ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-487
OCTOBER 3, 2019
PREPARED FOR:
KENT AND DAWN DORR
14350 MARIPOSA STREET
WESTMINSTER, COLORADO 80031
(jidorr4113$11.e.onl)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 6 -
UNDERDRAIN SYSTEM - 7 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 8 -
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. 0 Project No. 19-7487
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot S6, Filing 8, Aspen Glen, Saddleback 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 proposal for geotechnical
engineering services to Kent and Dawn Dorr dated August 16, 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, 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
Design plans for the residence had not been developed at the time of our study. In general, we
assume the proposed residence will be a two-story structure over crawlspace or basement level
with slab -on -grade garage floor. Grading for the structure is assumed to be relatively minor with
cut depths between about 4 to 8 feet. We assume relatively light foundation loadings, typical of
the proposed type of construction.
When building loadings, location and grading plans have been developed, we should be notified
to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The lot was vacant at the time of the field exploration. The terrain is relatively flat with a slight
slope down to the northeast with about 3 feet of elevation difference across the building site.
Kumar & Associates, in Project No, 19-7-487
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The ground surface is natural with minimal grading from road construction. Vegetation consists
of grass and weeds. Nearby buildings include one and two-story single family residences.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site and the
nearby areas of the Aspen Glen Development. 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 property. 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,
sinkholes have been observed scattered throughout the Roaring Fork River valley. These
sinkholes appear similar to others associated with the Eagle Valley Evaporite in other areas of
the Roaring Fork River valley. The nearest mapped sinkhole is located about'/ mile southeast
of this lot.
Sinkholes were not observed in the immediate area of the subject 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 S6 throughout the service life of the proposed residence, in our
opinion, is low and similar to other lots in Aspen Glen; however, the owner should be 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 project was conducted on August 20, 2019. 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 augers powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Kumar & Associates,Project No. 19-7-487
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Samples of the subsoils were taken with 1% 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 below about'/2-foot of topsoil consist of 11 to 14 feet of stiff to very stiff, sandy silty
clay overlying slightly silty sandy gravel with cobbles and possible boulders down to the
maximum depth explored, 20 feet. Drilling in the coarse granular soils with auger equipment
was relatively difficult due to the cobbles and boulders in the deposit.
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, presented on Figure 4, indicate low to
moderate compressibility under conditions of loading and a minor to low expansion potential
when wetted under a constant light surcharge. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The upper clay soils appear to possess an expansion potential when wetted. It has also been our
experience with the developed lots on Saddleback Road that the soils can also be collapsible
when wetted. The variable expansion/compression potential could result in movement of
footings bearing on the soils if they become wetted. Surface runoff, landscape irrigation, and
utility leakage are possible sources of water which could cause wetting. A lower risk alternative
would be to place the foundation entirely on the underlying relatively dense gravel soils or
remove and replace a certain depth of the clay soils with compacted structural fill. The subgrade
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should be observed for bearing conditions and further evaluated for heave/settlement potential at
the time of construction.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on at least
3 feet of compacted structural fill or on the natural gravel subsoils. If a deep foundation is
proposed, we should be contacted for additional recommendations.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on at least 3 feet of structural fill over the clay soils should be
designed for an allowable bearing pressure of 2,000 psf. Based on experience, we
expect initial settlement of footings designed and constructed as discussed in this
section will be about 1 inch or less. There is a heave/settlement potential for the
clay soils if they were to become wetted. The movement would be differential
and could be around an additional 1 inch for a wetted depth on the order of 8 feet
below footing bearing level. Use of a full depth basement would reduce the
movement potential with less depth of clay soils below the foundation bearing
level.
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
of foundations 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
Kumar & Associates, nc. Project No. 19.7.487
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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. The clay soils should be
removed for 3 feet below footing grade and the design bearing level re-established
with compacted structural fill to reduce heave potential. The fill should be a
relatively well graded granular material such as CDOT Class 6 (3/ -inch) road base
compacted to at least 98% of standard proctor density at a moisture content near
optimum. The fill should extend laterally beyond the footing a distance at least
equal to one-half the depth of fill below the footing.
6) A representative of the geotechnical engineer should test the structural fill during
placement for compaction and 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 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.
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
Kumar & Associates, Inc. ?' Project No, 19-7467
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walkway areas should be compacted to at least 95% of the maximum standard Proctor density.
Care should be taken not to over -compact 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. 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 0.45 for gravel fill bearing soils. 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 a
nonexpansive material 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, can be used to support lightly loaded slab -on -grade
construction with a risk of movement and distress if the bearing soils become wetted. The risk of
slab movement can be reduced by removing the clay soils and placing at least 2 feet of
compacted structural fill, such as road base, below the slab. 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 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.
Kumar & Associates, Inc, ' Project No, 19.7487
-7 -
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 3% -inch
road base or imported granular soil devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
this area and where there are clay soils 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 or sump and pump. 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 11/2 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 grading and surface drainage will be critical to limit potential for wetting below the
foundation and building distress. The following grading and drainage precautions should be
observed during construction and maintained after the residence has been completed:
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.
Kumar & Associates, Inc. ` Project No. 19-7487
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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 0 feet in paved areas. Free -draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site 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
10 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 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.
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
Kumar & Associates, Eric. Project No, 19-7-487
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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,
H -P K JMAR
Steven L. Pawlak, P.
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
Cc: F and M Architects — Flynn Stewart-Severy (flynn cr fandmarchitects.com
Kumar & Assoc at s, Inc. o Project No, 194-487
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19-7-487
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
L.1
LJ
w
w
0
- 0
5
- 10
- 15
— 20
BORING 1
EL. 6061'
BORING 2
EL. 6063.5'
18/12 / 18/12
WC=5.4
WC=5.0
D0=107
DD=108
-200=78
/
7/12 ] 12/12
WC=10.8 / WC=5.8
DD=107 // DD=111
-200=89 /
/
/
11/12 f `] 14/12
WC=8.6
/ / DD=107
/ -200=86
50/6
50/5
b: 50/3
0
5
10
15 ----
20
-- 25 25
19-7-487
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
of
LEGEND
7
l
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, BROWN.
CLAY (CL); SILTY, SANDY, STIFF TO VERY STIFF, SLIGHTLY MOIST, MIXED BROWN, LOW
PLASTICITY.
GRAVEL (GM --GP); SLIGHTLY SILTY, SANDY, COBBLES, POSSIBLE BOULDERS, SLIGHTLY
MOIST. BROWN, ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
11 DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
18/12 DRIVE SAMPLE BLOW COUNT. INDICATES TI -IAT 18 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 20, 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.
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).
19-7-487
Kumar & Associates
LEGEND AND NOTES
Fig. 3
!1:n{\f97L37.tltd.p
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
2
}
0
—1
— 2
— 3
0
— 2
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 CSD 2.5'
WC = 5.0 %, DD = 108 pcf
Th,,. 1111 rs, J vpp ' an ryty lhlh.
no1.,1.d. m. 11 rt:n0 pert
t a. ,,prnduc.d, eK.pi in
hltl, without the o,ttlen opprovel of
Kurrgr ,n.d M,ndbt.1, lm. SYN
Co.n dation 11WIIq pertwmld N
occordonc. .Hh ►5t►1 p -AS R
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
APPLIED PRESSURE - KSF 10 100
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 ® 5'
WC = 5.8 %, DD = 111 pcf
II"
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
10 APPLIED PRESSURE - KSF 10 100
19-7-487
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
K+11
Kumar & Associable, ittG.$
Geotettinicar and MaterlaFs Engineers
and i~mrirartmenta( Scientist
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Pro.eet No. 19-7-487
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITYo
(acfl
GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(asfl
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(,�o)
SAND
(/°)
LIQUID LIMIT
(%)
PLASTIC
INDEX
V.)
1
21/2
5.0
108
Sandy Silty Clay
5
10.8
107
89
Sandy Silty Clay
2
21/2
5.4
107
78
Sandy Silty Clay
5
5.8
111
Sandy Silty Clay
10
8.6
107
86
Sandy Silty Clay