HomeMy WebLinkAboutSubsoils Study for Foundation Designl(tÄiffi,;;ffifüf*r'x'å'*"
An Employca otmcd Çompony
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), Parkeq Colorado Springs, Fort Colling Glenwood Springs, and Summit County, Colorado
November 5,2021
Crawford Design Build
Attn: Simon Bentley
P.O. Box 1236
Carbondale, Colorado 81623
cdbsimon@comcast.net
Project No.2l-7-701
Subject: Subsoil Study for Foundation Design, Proposed Duplex Residence,
15 Sweetgrass, Lot D-20, Aspen Glen Subdivision, Garfield County, Colorado
Dear Simon:
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 Crawford Design Build dated August26,202l. The data obtained and
our recommendations based on the proposed construction and subsurface conditions encountered
are presented in this report.
Proposed Construction: The will be a wood frame structure over a
crawlspace. The attached garuge will be slab-on-Cut depths are expected to range
between about 2 to 5 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 site was vacant at the time of our site visit. The lot is relatively flat with a
gentle slope down to the south. Vegetation consists of grass and weeds.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
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 lzfoof of topsoil, consist of
medium stiff, sandy clay and silt down to the bottom of the pits at 6 to 7 feet. Results of swell-
consolidation testing performed on relatively undisturbed samples of the sandy silty clay soils,
presented on Figured 3 and 4, indicate low compressibility under existing moisture conditions
and light loading and a low collapse potential (settlement under constant load) when wetted. No
free water was observed in the pits at the time of excavation and the soils were slightly moist to
moist.
1
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 soil designed for an allowable soil bearing pressure of
1,500 psffor support of the proposed residence. The soils tend to compress after wetting and
there could be some post-construction foundation settlement. Footings should be a minimum
width of 18 inches for continuous walls and2 feet for columns. Loose and disturbed soils and
existing fill encountered at the foundation bearing level within the excavation should be 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 "t tgf!6 itctt* Uelow 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 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.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly to
moderately 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 3/+-inch road base gravel should be placed beneath garage and
patio slabs for support.
All fill materials for support of floor slabs should be compacted to at least95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: Shallow crawlspaces, less fhan 4 feet deep, should not require an
underdrain. We recommend that deeper crawlspaces be protected from wetting and hydrostatic
pressure buildup by an underdrain system.
If needed, 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 I foot below lowest adjacent finish grade and
sloped at a minimum lYo to a suitable gravity outlet. Free-draining granular material used in the
underdrain system should contain less than 2o/o passing the No. 200 sieve, less than 50% passing
Kumar & Associates, lnc. @ Project No. 2'l-7-701
-3-
the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
least 1lz 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: The following drainage precautions should be observed during construction
and maintained at all times after the duplex residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction. Drying could increase the expansion potential of the soils.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90o/o of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltration.
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
I % inches in the first l0 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. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation caused by inigation.
Limitations: 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. 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
those described in this report, we should be notified at once so re-evaluation of the
recommendations may be made.
Kumar & Associates, lnc. @ Project No. 21-7-701
-4-
This report has been prepared for the exclusive use by our client for design pulposes. \V'e are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services dwing construction to review and
monitor the implementation of our recommendations, and to veriff that the recomme,lrdations
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.
Daniel E. Hardin. P
DEHlkac
attachments Pits
Pits
Figure 3 8.4 - Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
Figure I
Figure 2
r.(h{Lt
2U4g
Kumar & Associates, lnc. @ Project No. 21-7-701
t
2502550
APPROXIMATE SCALE-FEET
21 -7 -701 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
ı
Ê
Þ
¡
3ø
E¡
Él¡'Ì
PIT f
EL. 100.5'
PIT 2EL.10l'
0 0
f-
t¡J
LJl!
ITFfL
t¡Jô
5
WC=5.5
DD=92
-2QQ=82
F
Ld
t¡JtL
I-FfLt!ô
WC=4.8
DD=9 1
5
10 10
LEGEND
TOPSOIL; ORGANIC CLAY AND SILT, SANDY, FIRM, MOIST, BROWN WITH ROOTS.
CLAY AND S|LT (CL-ML); SANDY, MEDTUM ST|FF, SL|GHTLY MO|ST, REDDTSH BROWN,
CALCAREOUS.
F
HAND DRIVE SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON AUGUST 26, 2021
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. TI{E ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL.
4. ÏHE 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. GROUNDWATER WAS NOT ENCOUNTERED IN THE PIÏS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7, LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCt) (ASTU D 2216);
-2AO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 40).
21 -7 -701 Kumar & Associates LOGS OF EXPLORATORY PITS Fis. 2
SAMPLE OF: Sondy Silty Cloy
FROM:Pit1@3'
WC = 5.5 %, DD = 92 pcf
-2OO = 82 %
)
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
\
\
\
\
I )
\
\
\
rËa B EUE oPdy ont þ uc
þmd$ l..'d.d, lh. t.Ung Þpo¡t
rholl not bc ruFde.d, .xc.pt l¡
lull, ithod h. rtun oppMol ol(umor orÈ kElob+ læ. Sr.ll
:6n olldotlon td{ñ¡ Flom.d lñ1.6úñ.. ¡nh M D-96-
1
o
^-1às
Jôt-z
l¡J
=ln
r_5
zotr
e- -+o
at1z.oo_5
-6
-7
-8
't.0 APPLIED PRESSURE - KSF 10 1
21 -7 -701 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
Ê¡
I
E
*
SAMPLE OF: Sondy Silty Cloy
FROM:Pit2(Ð5'
WC = 4.8 %, DD = 91 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
I
(
\
\
\
lÉ. tad @uru qpÈy ony b u6
æmpl6! lrrt d. ¡hr t rt¡ng Eport
rholl not b. Þfdxcd, .rcâpl ln
full, rlthôut tha údbn opÞMl ot
Kumo¡ ond
^ßælotd,
lß. Sr.ll
CoMlldotlon tðtlñg Flom.d ln
oæ!r&ñê. rnh ASIU D-4346.
2
ñ 0
J^J'z
l¿l
=vt
t-4
zotr
ô¡-ootnz.oo_g
-10
-12
-'t4
1.0 APPLIED PRESSURE - KSF t0
21 -7 -701 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fis. 4
I
E
*
l(t I äffiå*Jmo"tmå,','Êü,.*,
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No. 21-7-701
SAMPLE NATURAL
MOISTURÊ
CONTENT
NATURAL
DRY
DENSTTY
ATTERBERG
PIT DEPTH
GRAVEL SAND PERCENT
PASSING NO.
200 stEVE
PLASTIC
INDÐ(
UNCONFINED
COMPRESSIVE
SÏRENGTH
P/"1 P/"1
LIQUID LIMF SOIL WPE
1 -t 5.5 92 82 Sandy Silty Clay
2 5 4.8 9l Sandy Silty Clay