HomeMy WebLinkAboutSubsoils Report for Foundation Designrcn fliffiLffiTfffiniiyi*"'
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
Offrce Locations: Denver ([IQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
ST]BSOIL STTTDY
X'OR F'OT]NDATION DESIGN
PROPOSED RESIDENCE
LOT S4, X'rLrNG 8, ASPEN GLEN
567 SADDLEBACK ROAI)
GART'IELD COUNTY, COLORATIO
PROJECT NO. 23-7-516
ocToBER 19,2023
PREPARED X'OR:
PEAK 3 CONSTRUCTION
ATTN: JEF.F.CLAFLIN
310 MARKET STREET
BASALT, COLORADO 81621
ieff@peak3aspen.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY I
I
I
I
PROPOSED CONSTRUCTION
SITE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION ..........2-
SUBSURFACE CONDITIONS ...,,...2 .
FOUNDATION BEARING CONDITIONS............... .......... 3 -
DESIGN RECOMMENDATIONS ........................- 3 -
FOUNDATTONS ........- 3 -
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
....- 4 -
f-
UNDERDRAIN SYSTEM ............5.
SURFACE DRAINAGE.......
LIMITATIONS -6-
FIGURE I - LOCATION OF DGLORATORY BORINGS
FIGURE 2 . LOGS OF DGLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGI.JRE 4 - SWELL.CONSOLIDATION TEST RESULTS
TABLE 1. SUMMARY OF LABORATORY TEST RESULTS
-6-
Kumar & Associates, lnc. o Project No. 23-7-516
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PT]RPOSE AI\ID SCOPE OT'STT]DY
This report presents the results of a subsoil sfudy for a proposed residence to be located on Lot
S-4, Filing 8, Aspen Glen, 567 Saddleback Road, 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 Peak 3 Construction dated August 28,2023.
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 analyzed to 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 two-story wood-frame structure with attached garage. Ground
floors could be structural over crawlspace or slab-on-grade. Grading for the strucfure is assumed
to be relatively minor with cut depths between about 3 to 8 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 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 2 feet of elevation difference across the buildingarca.
The ground surface is natural with minimal grading from road construction. Vegetation consists
of grass and weeds with scattered sage brush. Nearby buildings include one and two-story,
single-family residences. There is an existing pond to the south of the lot.
SI]BSIDENCE 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
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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 arca,
sinlilroles have been observed scattered throughout the lower 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 a half 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 atthe site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot S-4 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 sinlfiole development. If further investigation of possible cavities in the
bedrock below the site is desired, we should be contacted.
F'IELD EXPLORATION
The field exploration for the project was conducted on September 19,2023. 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.
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-l586.
The penetrafion 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.
STIBST]RFACE COI\DITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. T\e
subsoils encountered, below about Yz foot of topsoil, consist of ll% to 13% feet of stiff sandy
silty clay overlying very dense,yar! sandy gravel and cobbles down to the maximum depth
explored of 15 feet. Drilling in the dense granular soils with auger equipment was difficult due
to the gravel and cobbles and drilling refusal was encountered in the deposits.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and finer than sand size gradation analyses. Results of swell-consolidation testing
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performed on relatively undisturbed drive samples, presented on Figure 4, indicate low
compressibility under light loading and a moderate expansion potential when wetted under a
constant light surcharge.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
X'OT]NDATION BEARING COI\DITIONS
The upper clay soils appedr to possess a moderate expansion potential when wetted but it has
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
movement 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 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 nafural 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.
l) Footings placed on at least 3 feet of structural fill over the clay soils should be
desigued 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 I 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 I inch for a wetted depth on the order of 6 feet
below footing bearing level. Use of a fuIl depth basement would reduce the
movement potential with less depth of clay soils below the foundation bearing
level.
2) The footings should have aminimum width of 16 inches for continuous walls and
2 feet for isolated pads.
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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
axea.
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 desigued 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 to expose the
natural clay soils. The clay soils should be removed for 3 feet below footing grade
and the design bearing level re-established with compacted structural filI to
reduce settlement/heave potential. The fill can consist of the onsite excavated
soils or a relatively well graded granular material such as CDOT Class 6 (%-inch)
road base compacted to at least 98% of standard proctor denstty 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.
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 arcIaterally 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 bacldrll 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 tateral 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 recofllmended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloprng 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 manimum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
3)
4)
s)
6)
Kumar & Associates, lnc. @ Project No.23-7-516
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walkway areas should be compacted to at least9iYo of the ma:rimum 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 lateralpressure 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 coefEcient of friction of 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated usrng 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 Iateral loads should be compacted to at least 95Yo of the
manimum standard Proctor density at a moisfure content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade
construction such as the garage floor 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
placrng 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 2Yopassing the No. 200
sieve.
All fiIl materials for support of floor slabs should be compacted to at least 95%o of maximum
standard Proctor density at a moisfure content near optimum. Required fill should consist of
t/+-inchroad base or imported gtanular 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
this area and where there are clay soils that local perched groundwater can develop during times
Kumar & Associates, lnc. @ Project No.23-7-516
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of heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan cteate 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 aurtdat least 1 foot below lowest adjacent finish grade and sloped at a minimum l%oto
a suitable gravity outlet, drywell into the underlying gravel or sump and pump. Free-draining
granular material used in the underdrain system should contain less than 2Yopassing the No. 200
sieve, less than 50% passing the No. 4 sieve and have a manimum size of 2 inches. The drain
gravel backfill should be at least lYzfeet deep. An impervious membrane, such as 20 mil PVC,
should be placed beneath the drain gtavel in a trough shape and attached to the foundation wall
with mastic to prevent wetting of the bearing soils.
SURJACE 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:
l) 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 95Yo of the morimum 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
3 inches in the first l0 feet in paved areas. Free-draining wall backfill should be
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
l0 feet from foundation walls. Consideration should be given to use of xeriscape
to reduce the potenfial for wetting of soils below the building caused by irrigation.
LIIT4ITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this arca at this time. We make no warranty either express or implied.
Kumar & Associates, lnc. @ Proiect No. 23-7-516
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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 rqlort, 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 clie,nt 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 veriry 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 sffata and testing of strucfural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar & Associate$, lnc.
./t / A-r'4.--
Paul J. Graf, Staff Engineer
Reviewedby:
a
Daniel E. Hardin,
PJG/kac
1o/r<(>j
Kumar & Associates, lnc. @ Project No.23-7.516
SADDLEBACK ROAD
',r'r j;'c p
::.::
1.
I
I BORING 2
ir
\-_._\ ,_\LOT 53
LOT 55 \'"
a _\
LOT 54
14,404.86 SQ.FT
0.33 acres
\
\
557 SADDLEBACK ROAD
I
APPROXIMATE SCALE-FEET
23-7-516 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
!
BORING 1
EL. 6,059
BORING 2
EL. 6,057.5'
13/12
tl,lC=7.7
DD=1 00
0
1o/12
WC=7.8
DD=89
-2OO=71
5
1O/12 13/ 12
WC=12.2
DD= 1 09
-200=85
5
Flrllrll!
IIFIL
l4Jo 13/ 12
Flrllrjl!
I-Fo-uto
10
8/ 12
WC= 14.5
DD=102
10
87 /12
so/6
15 15
LOGS OF EXPLORATORY BORINGS Fig. 223-7-516 Kumar & Associates
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LEGEND
N
TOPSOIL; CLAY, SANDY, SILTY, SCATTERED ORGANICS, FIRM, SLIGHTLY MOIST,
LIGHT BROWN.
CLAY (CL); SILTY, SANDY, sTlFF, SLIGHTLY MOIST, BROWN To LIGHT BROWN.
ffi
liiJ
SAND AND GRAVELS (SU-CU); SLIGHTLY SILTY, VERY COBBLEY, VERY DENSE,
SLIGHTLY MOIST, TAN.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
I DRTVE SAMPLE, 1 S/9-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST.
1A'1^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 10 BLOWS OF A 140-POUND HAMMERtvl ta FALLTNG Jo TNcHES wERE REeUTRED To DRrvE THE sAMpLER 12 tNcHEs.
I eucncaL AUGER DRTLLTNG REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 19,2023 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 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 BOR]NGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSTTY (pct) (lSrU D2216);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
23-7 -516 Kumar & Associates LEGEND AND NOTES Fig. 3
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N
5
SAMPLE OF: Sondy Silty Cloy
FROM:BoringlOg'
WC = 1 4.5 %, DD = 102 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
JJlrleo
I
z.o
-l
o
=oat7 _.,z. 1o()
N
JJ
lrJ
=a
I
zo
F
o
Joazo(-)
1
-3
-4
1
0
1
-2
-5
100PRESSURE - KSF t0t
1 t.0 APPLIED
SAMPLE OF: Sondy Siliy Cloy
FROM:Borlng2e^2'
WC = 7.7 %, DD = 100 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
23-7-516 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
rcn**Ugi1[r;i'-"
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Sandy Silty Clay
SOILTYPE
Sandy Silt and Clay
Sandy Silty Clay
Sandy Silty Clay
{osfl
u1{co1{FtNED
colrPRESStVE
SIREI{GTH
iLlx[s
PLASNC
INDEX
{%l
AT
r%l
LIQUID lJilT
83
7I89
102
100
10912.2
7.8
t4.s
7.72
4
2
9
I
2
GRADANOilSATPLE LOCANOil
DEPIHBORIl{G
PERCENT
PASSNG 1{0.
200 slEt E
I{ATURAL
DRY
DEilSTTY
I{AIURAt
ilOFruRE
COilTENT
SAI{D
(%)
GRAVEL
(%)
No.23.7.516