HomeMy WebLinkAboutSoils Report 04.30.20201(+A
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
ACEC
MEMBER
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kurrarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs and Summit County, Colorado
April 30, 2020
Gruenefeldt Construction
Attn: Dan Gruenefeldt
P.O. Box 1910
Basalt, Colorado, 81621
dan@p,ruenefeldt.com
Subject:
Dear Dan:
Project No. 20-7-234
Subsoil Study for Foundation Design, Proposed Residence, Lot E20, Aspen
Equestrian Estates, 25 Equestrian Way, Garfield County, Colorado
As requested, Kumar & Associates 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 you dated April 22, 2020. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: The proposed residence will be a one to two story wood frame
structure located on the site in the area of the pits shown on Figure 1. Ground flbor will be slab -
on -grade. A monolithic slab foundation is being considered. Cut depths are expected to range
between about 1'/2 to 3 feet. Foundation loadings for this type of construction are assumed to be
relatively light and typical of the proposed type of construction.
If building conditions or foundation loadings are significantly different from those described
above, 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 and is vegetated with grass and weeds. Some willows and deciduous trees are
located to the east of the lot along an existing ditch. Eagle Valley Evaporite bedrock is exposed
on the valley hillsides to the north and south of the property.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
five 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 foot of topsoil, jconsist of 2 to
Gruenefeldt Construction
April 30, 2020
Page 2
4 feet of medium stiff to stiff, sandy silty clay overlying relatively dense, silty sandy gravel with
cobbles and small boulders down to the maximum depth explored, 3% to 6 feet. Results of
swell -consolidation testing performed on a sample of the clay soil are presented on Figure 4 and
results of a gradation analysis performed on a sample of the gravel are presentedon Figure 5.
The laboratory test results are summarized in Table 1. Free water was not encountered in the pits
at the time of excavation and the soils were moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction
placed on the undisturbed natural clay or natural gravel soil
designed for an allowable soil bearing pressure of 1,500 psf for support of the proposed
residence. The clay soils tend to compress under load and there could be some post -construction
foundation settlement of around 1 inch. Footings or the thickened slab edge should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. The topsoil and loose
disturbed subsoils encountered at the foundation bearing level within the excavation should be
removed and the footing or thickened edge bearing level extended down to the undisturbed
natural soils. We should observe the completed foundation excavation prior to concrete
placement. 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. Shallower footings or thickened slab edges should be protected
from frost with insulation in accordance with the International Residential Code. 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 50 pcf for the on-site soil as backfill.
thickened edge slab foundation
we recommend spread footings or a
Non -Structural 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 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 interior slabs to
Kumar & Associates, Inc. Project No. 20-7-234
Gruenefeldt Construction
April 30, 2020
Page 3
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. Building
floor slabs should additionally be underlain by an impervious membrane.
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
onsite gravel soils devoid of vegetation, topsoil and oversized rock or an imported gravel such as
road base.
Underdrain System: An underdrain should not be needed for the proposed slab -at -grade
construction.
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
2'/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
Kumar & Associates, Inc. Project No. 20-7-234
Gruenefeldt Construction
April 30, 2020
Page 4
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
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.
Sincerely,
Kumar & Associates, Inc.
Daniel E. Hardin,
Reviewed by:
Steven L. Pawlak, P.E.
DEH/kac
attachments
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Table 1 —
— Location of Exploratory Pits
— Logs of Exploratory Pits
— Legend and Notes
— Swell -Consolidation Test Results
— Gradation Test Results
Summary of Laboratory Test Results
Kumar & Associates; Inc.
Project No. 20.7-234
LOT E-19
PIT 2
■
PIT 1
■
15 0 15 30
APPROXIMATE SCALE -FEET
LOT E-20
PIT 5
■
EQUESTRIAN WAY
PIT 3
■
PIT 4
20-7-234
Kumar & Associates
LOCATION OF EXPLORATORY PITS
Fig. 1
w
W
2
H
w
0
PIT 1
PIT 2 PIT 3
0
5 5
-- 0
5
PIT 4
PIT 5
WC=15.4
DD=108
7-7
+4=64
-200=10
0 —
5
10 10..
20-7-234
Kumar & Associates
LOGS OF EXPLORATORY PITS
Fig. 2
LEGEND
TOPSOIL, ORGANIC SANDY SILTY CLAY WITH ROOTS, SOFT, MOIST, DARK BROWN.
CLAY (CL): SILTY, SANDY, MEDIUM STIFF TO STIFF, MOIST, BROWN.
J
GRAVEL (GM—GP): SANDY WITH COBBLES, SLIGHTLY SILTY, MOIST, MEDIUM DENSE TO DENSE,
LIGHT BROWN.
SI HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE.
r,
DISTURBED BULK SAMPLE.
I
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON APRIL 24, 2020.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY! BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
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 DIGGI G. 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).
20-7-234
Kumar & Associates
LEGEND AND NOTES
Fig. 3
1
—1
W
3
I —2
z
0
1-
J
0
111
z
O
0 —d
•
SAMPLE OF: Sandy Silty Clay
FROM: Pit 5 0 2'
WC = 15.4%,DD= 108 pcf
Th.. UR multi opf•ti, odirbthi
WI. IN ti*pft
ahe4 ha osp.odVeW. unapt if
M4 •Flwro( the 1.01.1ln opprorol of
Nwnor and Hwolohw 40.
Coroarietion t0, pwtenmW in
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
7
T
10 APPLIED PRESSURE — KSF
10 100
20-7-234
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
100
90
80
70
so
SO
40
30
20
10
0
HYDROMETER ANALYSIS
SIEVE ANALYSIS
24 HRS
.118_. Rik
7 NRS
10 Ii1L =
TINE READINGS
•
J55
1209.._-_f-1
U.S.
STANDARD
II1Lit
SERIES
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CLEAR SOUARE
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127
20
DIAMETER OF PARTICLES 1141 MILLIMETERS
CLAY TO SILT
GRAVEL 64 X
LIQUID LIMIT
SAND
GRAVEL
FINE
MEDIUM
COARSE
FINE
COARSE
COBBLES
SAND 26 X
PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sandy Gravel with Cobbles
SILT AND CLAY 10 X
FROM: Pit 5 0 5'-5.5'
0
10
20
30
40
SO
BO
70
80
80
100
Thee* trot result' oppiy only to the
eomptee which were tested. The
!ogling report shall nal M reproduced.
..ceps in fu11, without the written
approval of ICumor & Associates. no.
Sieve anaiyr11 feeling H performed In
occordance wish ASTM 08513. AST4 07928,
ASTM C136 and/or *MIA DS 140.
20-7-234
Kumar & Associates
GRADATION TEST RESULTS
Fig. 5
Kumar& Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(acfl
GRADATION
PERCENT
PASSING2 SIEVE
ATTERBERG LIMBS
UNCONFINED
COMPRESSIVE
STRENGTH
(aafl
'
SOL TYPE
PIT
DEPTH
(rt)
GRAVEL
)
SAND
(%)
LIQUID LIMIT
(%)
PLASTIC
INDEX
(%)
5
2
15.4
108
Sandy Silty Clay
5-5'/2
64
26
10
Slightly Silty Sandy Gravel
with Cobbles