HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.04.2020KLA
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Geotechnical and Materials Engineers
and Environmental Scientists
An Employee Owned Company
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
February 4, 2020
Keila Valenzuela
1853 County Road 109
Glenwood Springs, Colorado, 81601
(valenzcuc[u,gmail.com)
CEIVE
telaws►J
Project No.20-7-106
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot El5, Aspen
Equestrian Estates, 39 Equestrian Way, Garfield County, Colorado
Dear Keila,
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to Keila Valenzuela dated January 13, 2020. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: At the time of our study, design plans for the residence had not been
developed. The.building is proposed in the area roughly between exploratory pit locations
shown on Figure 1. We assume excavation for the building will have a maximum cut depth of
about 2 to 4 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.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
Site Conditions: The lot was vacant at the time of our site visit. The lot is flat, slopes slightly
down to the south with around 2 feet of elevation difference across the lot. The site is vegetated
with grass and weeds. A drainage ditch is on the north side of the lot. Eagle Valley Evaporite
bedrock is exposed on the valley sides to the north and south. There was around
6 inches of snow cover at the time of our site visit. Two-story single-family residences and
Equestrian Way are to the south and northwest and vacant land is to the north and east of the site.
2
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
four exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 1/2 to 1 foot of topsoil, consist of
about 3'/2 to 51/2 feet of medium stiff to stiff, slightly sandy to very sandy silty clay underlain by
dense, slightly silty sandy gravel with cobbles and probable boulders. Excavating in the gravel
soils was difficult due to the cobbles and probable boulders and practical digging refusal was
encountered in Pit 3. Results of swell -consolidation testing performed on relatively undisturbed
samples of the clay soils, presented on Figure 3, indicate low to moderate compressibility under
conditions of loading and wetting. Results of a gradation analysis performed on a sample of
gravel (minus 5 -inch fraction) obtained from the site are presented on Figure 4. No free water
was observed in the pits at the time of excavation and the soils were slightly moist to very moist.
It should be noted that groundwater may rise in response to precipitation, snow melt, and
irrigation onsite and of the surrounding fields.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural clay soil or spread footings placed on the natural gravel soil for
support of the residence. Spread footings bearing on the natural clay soil should be designed for
an allowable soil bearing pressure of 1,200 psf. Spread footings bearing on the natural gravel
soils should be designed for an allowable soil bearing pressure of 3,000 psf. The clay soils tend
to compress under load and there could be post -construction foundation settlement up to about
1 inch. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for
columns. The topsoil and loose disturbed soils encountered at the foundation bearing level
within the excavation should be compacted or removed and the footing bearing level extended
down to the undisturbed natural soils. Exterior footings should be provided with adequate cover
above their bearing elevations for frost protection. Placement of footings at least 36 inches
below the exterior grade is typically used in this area. Continuous foundation walls should be
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 (if any) should be designed to
resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the
on-site soil as backfill.
Kumar & Associates, Inc. .a Project No. 20-7-106
-3 -
Non -Structural Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to
support lightly loaded slab -on -grade construction with the accepted risk of settlement and
movement. Structural floors as slab -on -grade could be used where the risk of movement cannot
be tolerated. To reduce the effects of some differential movement, non-structural 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 slabs to act as a break for capillary
moisture rise. This material should consist of minus 2 -inch aggregate with less than 50% passing
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
suitable onsite soils or imported gravel such as road base devoid of vegetation, topsoil and
oversized rock.
We recommend a vapor retarder conforming to at least the minimum requirements of ASTM
E1745 Class C material be used below slabs in living areas. Certain floor types are more
sensitive to water vapor transmission than others. For floor slabs bearing on angular gravel or
where flooring system sensitive to water vapor transmission are utilized, we recommend a vapor
barrier be utilized conforming to the minimum requirements of ASTM E1745 Class A material.
The vapor retarder should be installed in accordance with the manufacturers' recommendations
and ASTM E1643.
Underdrain 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 and crawlspace
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. An
underdrain should not be needed for floor slabs constructed at or above surrounding grade.
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
Kumar & Associates, Inc. Project No. 20-7-106
4
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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
21/2 inches in the first 10 feet in pavement and walkway 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
5 feet from the building.
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 pits excavated at the locations indicated on Figure 1
and to the depths shown on Figure 2, 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 pits and variations in the subsurface conditions may not become evident until
excavation is performed. If conditions encountered during construction appear different from
Kumar & Associates, Inc. 5 Project No. 20.7-106
-5 -
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 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.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, Inc.
Shane J. Robat, P.E.
Reviewed by:
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Steven L. Pawl , lz E.
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attachments Figur n of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 — Swell -Consolidation Test Results
Figure 4 — Gradation Test Results
Table 1 — Summary of Laboratory Test Results
Kumar & Associates, Inc. ,)
Project No. 20.7-106
DEPTH -FEET
0
5
PIT 1
EL. 100'
WC=20.4
DD=103
PIT 2
EL. 101'
PIT 3
EL. 101'
WC=18.6
DD=106
PIT 4
EL. 100'
1 WC=6.5
1 +4=68
—200=4
5
10 10
LEGEND
MTOPSOIL; SILTY CLAY, ORGANICS, FIRM, MOIST, BROWN.
/f
CLAY (CL); SLIGHTLY SANDY TO VERY SANDY, SILTY, MEDIUM STIFF TO STIFF, MOIST TO
VERY MOIST, BROWN.
GRAVEL (GP, GM); SLIGHTLY SILTY, SANDY WITH COBBLES AND PROBABLE BOULDERS,
DENSE, MOIST, MIXED BROWN. ROUNDED ROCK.
Sl HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE.
J
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JANUARY 15, 2020.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES AT THE SITE.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
PIT 1 AT 100', ASSUMED.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUND WATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
20-7-106
Kumar & Associates
LOGS OF EXPLORATORY PITS
Fig. 2
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
0
—1
— 2
—3
—4
— 5
0
4
SAMPLE OF: Slightly Sandy, Silty Clay
FROM: Pit 1 ® 4'
WC = 20.4 %, DD = 103 pcf
NO MOVEMENT UPON
WETTING
1.0 APPLIED PRESSURE — KSF 10 100
SAMPLE OF: Sandy Silty Clay
FROM: Pit 3 CSD 2.5'
WC = 18.6 %, DD = 106 pcf
Ah IS (lel ntwillI apply 414 la the
oomph. Seated. ih. t„Ileo 'apart
ehaa nal W nprea,u.d ncepl In
f..1 mahout the .Itthn approval of
Ihrmo[ snd Heev:elee. Inv. SUM
Co :{ppt on 4101 O '1 In
pvveidersn rilh J. 6-45411
NO MOVEMENT UPON
WETTING
1.0 APPLIED PRESSURE — KSF 10 10D
20-7-106
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 3
100
90
6O
70
60
50
49
30
20
10
HYDROMETER ANALYSIS
SIEVE ANALYSIS
TIME RE406638
24 HRS 7 HRS
45 MIN 15 14161 60}116 191416
. I
U.S. STANDARD SERIES
41.4I71 114IN 120a. 1100 0 ,./40/10 .// R18 99 04
0 I -11.1"
_1 I I '1__
.001 .002 . .019 .019
1
1
I
.1 1 1 111 1 I 1 4 1 1 1 11 1 1 1 1 I J LI11 I100
.037 .075 .160 .300 1 .600 1. B 12.36 4.75 9.5 19 1 I 36.1 I. ;Jim
I
76.2 127 204
DIAMETER OF PARTICLES IN MILLIMETERS '92 I
CLEAR SOUARE OPENINGS
3/4' 1 TY2' 3' .-'6" 6'6
10
20
1 ..
I
--- 30
40
50
60
i I 70
B0
90
CLAY TO SILT
SAND
GRAVEL
FINE MEDIUM
COARSE
FINE
COARSE
COBBLES
GRAVEL 68 % SAND 28 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Sandy Gravel with Cobbles
SILT AND CLAY 4 %
FROM: Pit 4 ® (-5'
These test results apply only to the
samples which were tested. The
1e4IIn9 report shall not be reproduced,
except In full, without the written
approval of Kurnor & Assocln1oo, Inc.
Slava analysis lasting Is performed In
accordance with ASTM D6913, ASTM D7928,
ASTM C156 and/or ASTM 01140.
20-7-106
Kumar & Associates
GRADATION TEST RESULTS
Fig. 4
gout & Associates, kw.
Geotechnical and Maater{eis Er freer.
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 20-7-106
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY(%)
(Pcf)
GRADATION
PERCENT
PASSING
G NO.E
ATFERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psfl
SOIL TYPE
BORING
DEPTH
(ff)
GRAVEL
SAND
(%)
LIQUID LIMIT
(%)
PLASTIC
INDEX
(%)
1
4
20.4
103
Slightly Sandy, Silty Clay
3
21/Z
18.6
106
Sandy, Silty Clay
4
4 to 5
6.5
68
28
4
Sandy Gravel with Cobbles