HomeMy WebLinkAboutSubsoils Study for Foundation Designl (+rt åiffi fi'trf:'fËtr*"'"å; ;' **5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@.kumarusa.com
wwwkutnarusa.comÂn fmploya* Ownad Ccnpony
Ofüce Locations: Denver (l{Q), Parker, Colorado Springs, Fort Coilins, Glenrvood Springs, and Sunmit County, Cololado
August 4"2023
James Gornick Building Specialists
Attn: Jim Gornick
1005 Cooper Avenue
Glenwood Springs, Colorado 8i601
ieornick 19BBCÐ.prnzil.com
Project No.23-7-407
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 1, River Ridge,
River Ridge Drive, Garfield Counfy, Colorado
Dear Jim:
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 James Gornick Building Specialists dated July 6,2023. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report.
Proposed Construction: Plans for the proposed residence v/ere conceptual at the time of our
study. The proposed residence will generally be a one- or two-story wood-frame structure with
attached garage and covered patio and detached unit located on the site approximately as shown
on Figure 1. uGround floors could be slab-on-grade or strucfural over crawlspace. Cut depths are
expected to range between about 2 to 6 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 subject site was vacant of structures and there was cut and fill grading for
the proposed residence at the time of our field exploration. The ground surface was relatively
flat and gently sloping in most of the building envelope then sloping down around 4 feet in
elevation in the southem part. Vegetation consists of grass and weeds with scattered scrub oak.
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 I foot of topsoil, mainly consist
of dense, silty sandy gravel with cobbles down to the maximum explored depth of 5 feet. A
layer of clayey silty sand and gravel was encountered in Pit 4 from i to 3 feet deep. Results of
gradation analyses performed on samples of silty sandy gravel and cobbles and clayey silty
a
gravelly sand (minus 3-inch fraction) obtained from the site are presented on Figure 3. No free
water was observed in the pits at the time of excavation and the soils were slightly moist.
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 gravel soil designed for an allowable soil bearing pressrre,of
2"500 psf for support of the proposed residence. The upper silty clayey soils tend to compress
after wetting and should be removed to limit post-construction foundation settlement. We should
observe the completed foundation excavation prior to placing footing forms. Stmctural filI
placed to reestablish design bearing level can consist of the onsite soils compacted to at least
98% of standard Proctor density at near optimum moisture content. Footings should be a
minimum width of l6 inches for continuous walls and 2 feet for columns. Topsoil, existing fill
and loose disturbed soils encountered at the foundation bearing level within the excavation
should be removed and the footing bearing level extended down to the undisturbed natural gtavel
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 a¡ea. Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least l0 feet. 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 50 pcf for backfill consisting of the on-site granular soils.
Cantilevered retaining structures which are separate from the residence and can be expected to
deflect sufficiently to mobilize the fulI 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 40 pcf
for backfill consisting of the on-site granular soils. Resistance to sliding at the bottoms of the
footings can be calculated based on a coefficient of friction of 0.45. Passive pressure of
compacted backfill against the sides of the footings can be calculated using an equivalent fluid
unit weight of 375 pcf. The coeffrcient of friction and passive pressue 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.
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
u¡restrained 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
Kumar & Associates, lnc. o Project No. 23-7-407
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layer of relatively well graded sand and gravel such as road base should be placed beneath slabs-
on-grade for support. This material should consist of minus 2-inch aggregate with less than 50Ya
passing the No. 4 sieve and less than l2o/o 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 fiIl can consist of the
on-site soils devoid ofvegetation, topsoil and oversized rock.
Underdrain System: Although free water was not encountered during our exploratìon, it has
been our experience in the areailtat 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-gtade construction, such as retaining walls and basement areas
(if any), be protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains should consist of rigid perforated PVC 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 ofexcavation and at least I foot below lowest adjacent finish grade and
sloped at a minimumYzo/o to a suitable gravity outlet. Free-draining granular material used in the
underdrain system should contain less than 2Yo passing the No. 200 sieve, iess than 50% passing
the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
leasf lYz feet deep and covered with filter fabric.
Surface Drainage: The following drainage precautions should be observed dwing construction
and maintained at all times after the residence has been completed:
l) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill shouid 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 90% of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on-site, finer graded soils to reduce surface water infiltration.
3) The ground swface 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
ZYz tncbes in the first l0 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this areaat this time. We make no warranty either
Kumar & Associates, lnc. o Project No. 23-7-407
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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 concemed
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 pu{poses. 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 verifu 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,
James H. Parsons,
Reviewed by:
ffi*/,
Steven L. Pawlak, P.E.
JHP/kac
uttuchments Figure I - Location of Exploratory Pits
Figure 2 * Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Table 1 * Summary of Laboratory Test Results
Kumar & Arsociates, lnc.6 Ptoject No. 23-7.407
PIT 2
PIT 1
I
I
.\
t,
t!ìri
f*\
\
PIT 3
\
\\.
1-
¿3
9i'
0
APPROXIMATE SCALE_FEET
23-7 -407 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
I
PIT 1
EL. 'l 00'
PIT 2
EL. 'l 0o'
PIT 3
EL. 1 00'
PIT 4
EL. 94'
0 0
F
L,J
L¡.]
L
IT
F-o-
LJrì
I
-
I
I
I
-- WC=3.7| +4=20
-200=33
Ft¡L!
Lr-
I
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LEGEND
TOPSOIL; SAND, SILTY, SCATTERED GRAVEL, ORGANICS, FIRM, SLIcHTLY M0lST, BROWN.
SAND AND GRAVEL (SC-GC); CLAYEY, SCATTERED COBBLES, SCATTERED oRcANlCS, MEDIUM
DENSE, SLIGHTLY MOISÏ, BROWN.
TOPSOIL; SAND, SILTY, SCATTERED GRAVEL, ORGANICS, FIRM, SLIGHTLY MolST, BROWN
t DISTURBED BULK SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 1'1,2023.
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 MEASURED BY HAND LEVEL AND REFER TO
PIT 1 AS A 1OO' ASSUMED BENCHMARK,
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE MEÏHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND ÏHE TRANSÍTIONS MAY BE GRADUAL.
6. GROUNDWATER 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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
WC=9.4
+4=62
-2O0=4
23-7 -407 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
ã
HYDROMETER ANALYSIS SIEVE ANALYS¡S
TIME REÂDINCS
24 HRS 7 HRs
J.S. SIÀNDARD SERIES
J50 ¡{ t50 ala ¡10 ¿a I
CLäR SOUARE OPEN¡NGS
3/A' 3/1' 1 I/r'¿100
I
II
l
loo
so
a0
70
60
50
40
20
l0
0
0
to
20
30
40
50
60
70
a0
90
t00
t9 58.1 74.2 127î.425
RS
CLAY TO SILT COBBLES
GRAVEL 62 % SAND 34
LIQUID LIM¡T
SAMPLE 0F: Slighlly Silly Sondy Grovol
PLASTICITY INDEX
SILT AND C[.AY 4 %
FR0M: Pít 2 @ 2,5 ond 5' Combined
3
100
90
go
70
60
40
30
20
to
o
o
10
20
30
40
60
70
ao
90
100
zf
76,2 127
1
IN ETE
CLAY TO SILT COBBLES
GRAVEL ?O % SAND
LIQUID LIMIT
SAMPLE OF: Sllty Cloyey Grovelly Sond
47%
PLASTICITY INÞEX
FROM:PiÌ4e.2.5'
SILT AND CLAY 33 %
Thsse lesl r6sllls qpply only lo lh€
somplos wh¡ch vsrs losl€d. lho
lô3llng r.pgrf shqll nol bo r6prodqc6d,
oxcopt ln full, vlthoul lhê wrltlôn
opprovol oT Kumqr & Asroclolos, lñc.
Sl€vo onolysls losllng ls porformod ln
occordonc6 wllh ASTM 06913, ASIM 07928,
ASTM C136 qndlor ASTM D11,10.
SAND GRAVEL
FINE MEDIUM COARSE FIN E COARSE
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME READINgS
¿4 HRS 7 HRS Í"
U.S. STANDÂRD SERIES CLEAR SOUARE OPENINCS
\/AD \/t 1 t/t'
.. ..1
SAND GRAVEL
FINE MEDIUM COARSE FIN E COARSE
x-7 - 4A7 Kumar & Associates GRADATION TEST RESULTS Fig.3
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TABLE 1
SUMMARY OF LABORATORYTEST RESULTS
No.23-7
SÂMPt
SOIL TYPE
lDsll
UNCONFINED
COMPRESSIVE
STRENGTH
PERCENf
PASSTNG 1lO.
2OO SIEVE
LIOUID UMTI
r%t (7.)
PLASI1C
INDEX
GRAVEL
{%)
SAND
(%)PIT
tftl
DEPTH
{"/"\
NATURAL
MOISTURÉ
CONTENT
NATURAL
DRY
DENSITY
lDcl)
Slightly Silty SandY Gravel4346222%&s
Combined 9.4
Silfy Clayey GravellY Sand332A474a l/z/2 3:7