HomeMy WebLinkAboutSoils Report 04.12.2019Ii[ 1-', Se M
&, d�F 3;
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 wvwv.kun1arusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
ik Ilf+eefi�•
RECEIVED
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 12, FOUR MILE RANCH
97 SUNRISE COURT
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-215
APRIL 12, 2019
PREPARED FOR:
HECTOR AND LIZZ SANTIAGO
101 WHITE HORSE PLACE
GLENWOOD SPRINGS, COLORADO 81601
visianbu iiders2015 k ail. c a nn
31/44...-1 ai Ye:v.'.
>•anYunNlrs�a(�
qr9-261 i
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOORSLABS -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
FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19-7-215
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
12, Four Mile Ranch, 97 Sunrise Court, 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 proposal for geotechnical engineering
services to Hector and Lizz Santiago dated March 29, 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
The proposed residence will be one and two story wood frame construction above a crawlspace
with an attached slab -on -grade garage located in the building envelope shown on Figure 1.
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 lot was vacant and vegetated with grass and weeds at the time of our study. The ground
surface slopes gently down to the northwest with about 5 feet of elevation difference across the
building area. Access onto the lot is from a shared driveway off the end of Sunrise Court.
Kumar & Associates, Inc. Project No. 19-7-215
-2 -
FIELD EXPLORATION
The field exploration for the project was conducted on April 8, 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 and
Associates.
Samples of the subsoils were taken with 1% inch and 2 -inch LD. 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 to 3 feet of topsoil, consist of stiff sandy silty clay down to about 7 feet
in Boring 2 and 101/2 feet in Boring 1 overlying dense, gravel, cobbles and possible boulders in a
silty clayey sand matrix. Below the gravel and cobble soil in Boring 2 at about 101/2 feet,
medium dense, silty clayey sand with gravel was encountered down to 26 feet where very hard
siltstone bedrock was encountered. Drilling in the coarse granular soils with auger equipment
was difficult due to the cobbles and boulders and drilling refusal was encountered at Boring 1.
Laboratory testing performed on samples obtained from the borings consisted of natural moisture
content and density, finer than sand size gradation and unconfined compressive strength. Results
of swell -consolidation testing performed on relatively undisturbed drive samples of the clay
soils, presented on Figures 4 and 5, indicate low compressibility under light loading and minor
collapse or expansion when wetted under light load. Unconfined compression strength testing on
the clay soil showed a stiff consistency. 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 moist.
Kumar & Associates, inc. Project No. 19-7-215
-3 -
FOUNDATION BEARING CONDITIONS
The residence as planned will be above a crawlspace and the clay soils will apparently be
exposed in the excavation base. A basement level (if provided) could extend down through the
clay and into the gravel and cobble soils with the garage excavation likely in the upper clay soils.
The upper clay soils have variable settlement/heave potential when wetted that could result in
post -construction building movement or distress. Care should be taken in the surface and
subsurface drainage around the house to prevent the bearing soils from becoming wet. It will be
critical to the long term performance of the structure that the recommendations for surface
grading and subsurface drainage contained in this report be followed. The amount of settlement
will mainly be related to the depth and extent of subsurface wetting of the clay soils. Extending
the foundations down to the granular soils or replacing the clay with compacted structural fill
could be done to achieve a lower risk of differential movement and distress.
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
on the natural soils or compacted structural fill.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils or compacted structural fill
should be designed for an allowable bearing pressure of 1,500 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. Additional movement of
about 'A to 1 inch could occur if the bearing soils are wetted.
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.
Kumar & Associates, Inc. Project No.19-7-219
-4_
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 12 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 undisturbed natural soils. The exposed soils
in footing area should then be moistened and compacted. Structural fill should be
a granular soil such as road base compacted to at least 98% of standard Proctor
density.
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 55 pcf for backfill consisting
of the on-site soils. Cantilevered retaining structures (if any) 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 50 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 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 slightly above 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
Kumar & Associates, Inc. Project No. 19-7215
-5 -
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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 300 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 compacted to at least 95% of the maximum
standard Proctor density at a moisture slightly above optimum.
FLOOR SLABS
The natural clay soils, below the topsoil, can be used to support lightly loaded slab -on -grade
construction with a risk of movement and distress. We recommend granular structural fill such
as road base be placed below slab areas to design subgrade level. 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 relatively well graded sand and gravel, such as road base,
should be placed beneath slabs for support. This material should consist of minus 2 -inch
aggregate with at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200
sieve. If a basement level is provided, the under slab gravel should be free draining with 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 should consist of
granular soils devoid of vegetation, topsoil and oversized rock.
Kumar & Associates, Inc. Project No. 19.7415
UNDERDRAIN SYSTEM
6
Although free water was not encountered during our exploration, it has been our experience in
the 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. 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.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times 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.
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 clay 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.
Kumar & Associates, Inc. Project No. 19.7-215
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
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 KIJMAR
Steven L. Pawlak,
SLP/kac
cc: Mike Henry (mikt. •atedmtn.com)-
Kumar & Associates, Inc. Project No.19.7-215
.\):1
nUgi
SUNRISE COURT
u+EC'
f
Riar
liot:40411110taak,
wr
5 r
HB
b z
N
� N
• 3
• a
BORING 1
97 SUNRISE
COURT
▪ BORING 2
•
c
8
30 0 30 60
APPROXIMATE SCALE -FEET
19-7-215
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
0
--- 5
---- 10
-- 15
'— 20
El
- 25
•--- 30
— 35
BORING 1
EL. 100'
14/12
WC -1 9.7
DD=105
26/12
WC=16.3
DD=111
—200=81
19/6, 43/6
BORING 2
EL. 95'
6/12
WC=19.3
DD=102
UC=2,200
17/12
�/ WC=17.3
DD=104
18/12
13/12
WC=9.0
DD=115
—200=43
25/12
1 50/1
0
5--
10 --•• —
15 --
20 -
25 —
30 --
35
f-
n.
Lu
0
19-7-215
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
•
LEGEND
-ti
ti
—7
7
14/12
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN.
CLAY (CL); SILTY, SANDY, STIFF, MOIST, BROWN, CALCAREOUS TRACES, LOW PLASTICITY.
GRAVEL AND COBBLES (GM–GC); SILTY, CLAYEY, SANDY, POSSIBLE BOULDERS, DENSE,
SLIGHTLY MOIST, BROWN, SURROUNDED TO SUBANGULAR ROCK.
SAND (SM–SC); SILTY, CLAYEY, SCATTERED GRAVEL, MEDIUM DENSE, MOIST, BROWN.
SILTSTONE BEDROCK; VERY HARD, SLIGHTLY MOIST, GRAY. EAGLE VALLEY FORMATION.
DRIVE SAMPLE, 2–INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8–INCH I.Q. SPLIT SPOON STANDARD PENETRATION TEST.
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 14 BLOWS OF A 140–POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 8, 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 MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS ELEV = 100', ASSUMED.
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);
UC = UNCONFINED COMPRESSIVE STRENGTH (psi) (ASTM D 2166).
19-7-215
Kumar & Associates
LEGEND AND NOTES
Fig. 3
1
.. 0
CONSOLIDATION - SWELL
—1
--2
— 3
— 4
T.uH teat !smug epp!/ 0.4 m 11..
pyue. a .leM.K4 70 ae4p e
MIwu. .ntion apporpd w
f[no
Nunc Ma MIodate& Mlc. Swat
deceadwaoa.Ltr�i e3L
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 2.5'
WC = 19.7 %, DD = 105 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - KSF 10
100
19-7--215
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
0
i\ - -1
—2
—3
— 4
— 5
— 6
CONSOLIDATION - SWELL
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 ® 5'
WC = 17.3 %, DD = 104 pcf
Thou era n.w. cppM c.y w I'.
Th. I• N rol
• g mi h. nprcdre.J, rxe.p 7n
fug, Othoirl
}NOW .rid Iawcfan.In. SNAP
eu a
1 ' �- i
1 I ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE - KSF 10 100
1r
19-7-215
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 5
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Proiect No.19-7-
SAMPLE LOCATION
NATURAL NATURAL
MOISTURE DRY
CONTENT DENSITY
(%) (PO
! GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(1361)
SOIL TYPE
BORING
DEPTH
t
GRAVEL
�(%)
I
SAND
(a�)
LIQUID LIMIT
[°/a}
PLASTIC
INDEX
{ ')
1
21/2
19.7
105
Sandy Silty Clay
5
16.3
111
81
__2
Sandy Silty Clay
2%2
19.3
102
Sandy Silty Clay
5
17.3
104
Sandy Silty Clay
15
9.0
115
43
Silty Clayey Sand
r
_
I-