HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.18.2022tGrtij,ffififfifffin,1iå*"'
An Employcc Ownrd Compony
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 Counry Colorado
August 18,2022
Brooks Design Build
Attn: Brian Hanlen
23 I Robins on Street, #226
Basalt, Colorado 81621
brian@brooksdesienbuild.com
Project No. 2l-7-382.1
Subject: Subsoil Study for Foundation Design and Septic Field, Proposed Residence,
Crystal River Ranch, 1508 County Road 108, Garfield County, Colorado
Dear Mr. Hanlen:
As requested, Kumar & Associates, Inc. performed a subsoil study for foundation design and
septic disposal feasibility at the subject site. The study was conducted in accordance with our
agreement for geotechnical engineering services to Brooks Design Build dated June 8,2022.
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 story wood frame structure over
a crawlspace located on the site as shown on Figure 1. Ground floors are proposed to be
structural over crawlspace. A det¿ched garage with slab-on-grade floor is proposed to the
northeast of the house. Cut depths are expected to range between about 3 to 6 feet. Foundation
loadings for this type of construction are assumed to be relatively light and typical of the
proposed type of construction. The septic disposal system is proposed to be located about
50 feet east ofthe house.
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 is currently vacant cow pasture which slopes gently down to the east
below an active irrigation ditch, located about a quarter mile northeast of the main ranch area.
The building area is relatively flat with slopes down to the east at about 3%oto 57o, down to the
east. Vegetation in the building area consists of grass. There are pinon trees to the west and
uphill of the building area. There is another active irrigation ditch located east and downhill of
the proposed building site.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits in the building arca and one pit in the septic disposal area at the
approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The
a
subsoils encountered, below about I foot of topsoil, consist of mostly medium stiff, sandy silty
clay down to the bottom of the pit depths of 7 to I feet. Siþ, sandy gravel with small cobbles
and rock fragments were encountered in Pit 1, closest to the upper irrigation ditch. Results of
swell-consolidation testing performed on relatively undisturbed samples of the sandy silty clay
soils, presented on Figures 3 and 4, indicate low compressibility under existing low moisture
conditions and light loading and a low to moderate potential under increased loading after
wetting. Results of a gradation analysis performed on a sample of slightly silty sand and gravel
(minus S-inch fraction) obtained from Pit l, are presented on Figure 5. A gradation/hydrometer
analysis of the loam soils encountered in the Septic Profile Pit are presented on Figure 6. The
laboratory test results are summarized in Table 1. No free water was observed 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, we recommend spread footings
placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf for
support of the proposed residence. Footings should be a minimum width of 20 inches for
continuous walls and 2 feet for columns. Loose and 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 soils. \Me should observe the completed foundation
excavation to confirm suitable bearing conditions. 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 heavily reinforced top and bottom to span local anomalies such as by assuming an
unsupported length of at least I2feet. Foundation walls acting as retaining structures should be
designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least
55 pcf for the on-site soil as backfill, excluding organics and rock larger than 6 inches.
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.
All fill materials for support of floor slabs should be compacted to at least 95/ø otmaximum
standard Proctor density at a moisture content near optimum. Required fill can consist of
imported granular soils such as3/¿-inch road base devoid of vegetation, topsoil and oversized
rock.
Kumar& Associates, lnc. @ Project No. 21-7-382.1
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Underdrain System: Although free water was not encountered during our exploration, there is
an active irrigation ditch uphill of the residence. We recommend below-grade construction, such
as retaining walls and crawlspace 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 I foot below lowest adjacent flrnish grade and sloped at a minimum lYoto
a suitable gravity outlet or sump and pump. Free-draining granular material used in the
underdrain system should contain less than 2Yo 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 IYz feet deep.
Surface Drainage: The following drainage precautions should be observed during 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 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 90Yo of the maximum st¿ndard 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 infìltration.
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 l0 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Septic Field: The soils exposed in the Profile Pit consist of USDA Loam soils to a depth of
8 feet. Based on the soil gradation shown on Figure 6, the soils are Type2. A civil engineer
should design the infiltration septic disposal system.
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 atthe locations indicated on Figure l,
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
Kumar& Associates, lnc. o Project No. 21-7-382.1
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(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.
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 implementadion of our recommendations, and to veriry 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, Ine.
(:"
Daniel E. Hardin,
Reviewed by:
Steven L. Pawlak, P.E.
DEH/kac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figures 3 and 4 - Swell-Consolidation Test Results
Figure 5 - Gradation Test Results
Figure 6 - USDA Gradation Test Results
Table I - Summary of Laboratory Test Results
Kumar & Associates, lnc. @ Project No. 21-7-382.1
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21-7-382.1 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1 PIT 2 PIT 3 PROFILE PIT
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ris, 2LOGS OF EXPLORATORY PITS21-7 -382.1 Kumar & Associates
LEGEND
FILL:
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HAND DRIVE SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JUNE 8, 2022,
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.o THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED BY INSTRUMENT SURVEY FROM
THE (insert).. THE EXPLORATORY PITS WERE LOCATED BY (insert).. THE LOCATIONS OF THE EXPLORATORY PITS WERE LOCATED BY GPS COORDINATES OBTAINED
FROM GOOGLE EARTHru AND LOCATED IN THE FIELD WITH A HANDHELD GPS UNIT.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPÏH.
4. THE EXPLORATORY PIT LOCATIONS 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 PITS AT THE TIME OF EXCAVATION. PIÏS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
Wc = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCt) (ISTU D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200= PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1140).
SAND = PERCENT PASSING No. 10 SIEVE AND RETAINED ON No. 325 SIEVE
SILT = PERCENT PASSING NO. 525 SIEVE TO PARTICLE SIZE .002MM
CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM
21-7 -382.1 Kumar & Associates LEGEND AND NOTES Fis. 3
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SAMPLE OF: Slightly Sondy Silly Cloy
FROM:Boring2@2'
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Fig. 4SWELL-CONSOLIDATION TEST RESULTS21-7 -382.1 Kumar & Associates
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SAMPLE OF: Slighfly Sondy Silty Cloy
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Fig. 521*7-382.1 Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS
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DIAMETER OF
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SAMPLE OF: S¡lty Cloyoy Sond
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PLASTICITY INDEX
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21-7 -382.1 Kumar & Associates GRADATION TEST RESULTS Fig. 6
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and Environmenlal Scientisls
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
sÀtlPt F ocÂTroit
S()lLTYPESLTı.CLAY
(%)
GRÀ\'EL
(%)
SA¡ID
(%)
S¡LT
(%)
ct¡Y
(%)
DFPIH
(ft)
IIATURAL
rro¡sfuRE
COI{IENT
(%)
I{ATURAJ-
DRY
DEilSTY
(pc0
GRAVEL
l'l"l
SAND
(Y")
PIT
Silty Sand and
Gravel4545l0I6to7
Slightly Sandy Silty
Clay2719.9 104
Slightly Sandy Silty
Clay320.4 l0t
43 36 2t LoamProfile
Pir 4to5