HomeMy WebLinkAboutSubsoils Report for Foundation DesignrcnU***nggg[r';-*5020 County Road 154
Glenrvood Springs, CO 81601
phone: (970) 945-7988
f'ax: (970) 945-8454
email: kaglenrvood@lcumantsa.com
wwrx'.hlmatusa.comAn Employee Owoed Compony
Ofrce Locatiorx: Denver (HQ), Parke4 Colorado Springs, Fort Collins, Gle.nq'ood Springs, and Suirunit Counfy, Cotorado
December 18,2023
Evan Wagstrom
P.O. Box 543
Glenwood Springs, Colorado 8i602
ervass67@smail.com
Project No. 23-7-689
Subject: Subsoil Study for Foundation and Septic Design, Proposed Residence, TBD Ram
Lane, Lat 2, Piffer Subdivision Exemption, Garfi eld C ounfy, Colorado
Dear Mr. Wagstrom:
As requested, Kumar & Associates, Inc. perfonned 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 you dated December 7,2023. The dara
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report.
Proposed Construction: We assulne the proposed residence will be a one to fwo-story wood
frame structure over a crawlspace located in the area of the pits as shown on Figure 1. Ground
floors are expected to be structural over crawlspace. Cut depths are expected to range between
about 3 to 5 feet. Foundation loadings for this tytrle of construction are assumed to be relatively
light aid typical of the proposed type of construction. The septic disposal system is proposed to
be located west of the 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 was vacant of sffuctures except for an old shed which will be
removed. The site appeared natural and vegetated with grass and scattered sage and juniper
trees. The terrain was gently rolling, generally down to the south.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits in the building area and one profile 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
subsoils encountered, below about I foot of topsoil, consist of moist, sandy silty clay. Results of
swell-consolidation testing performed on relatively undisturbed samples of the sandy silty clay,
presented on Figure 3, indicate low compressibility under existing moisture conditions and light
loading and a minor expansion/settlement potential when wetted. The sandy silty clay has low to
moderate settlement potential when loaded after wetting. Results of a USDA gradation analysis
performed on a sample of the sandy loarn frorn the proposed septic area Profile pit obtained frorn
a
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the site are presented on Figure 3. The laboratory test results are sunullarized 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 consffuction, we recorlmend spread footings
placed on the undisturbed natwal soil designed for an allowable soil bearing pressure of
2,000 psf for support of the proposed residence. The soils tend to compress after wetting and
th.t" "*ld% some post-construction foundation settlement. Footings should be a minimum
width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and
existing topsoil encountered at the foundation bearing level within the excavation should be
removed and the footing bearing level extended down to the undisturbed natural soils. We 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.Placenrentoffootingsatle@esbelowtheexteriorgradeistypicallyusedin
this area. Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assurning an unsupported length of at least 12 feet. 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 largerthan
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 reinforcernent 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 facilitate drainage. This rnaterial
should consist of minus 2-inch aggregate with less thar-l0% passing the No. 4 sieve and less
than2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95To of maxrmum
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: 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 nmoff can create aperohed
condition. We recommend below-grade consffuction, such as retaining walls, crawlspace and
basement areas (if any), be protected from wetting and hydrostatic pressure buildup by an
underdrain system.
Kumar & Associates, lnc. o Project No.23-7-689
-3-
The drains should consist of drainpipe placed in the bottom of the wall backflrll 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 lolo to
a suitable gravity outlet. 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 maxirnum size of 2 inches. The drain gravel backfill should be at least l% feet deep.
Surface Drainage: The following drairiage precautions should be observed during construction
and maintained at all times after the residence has been cornpleted:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during consffuction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95o/o of tbe 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 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
&ain away frorn 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 10 feet in pavement and walkway areas.
4) Roof downspouts and drains shouid 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 building caused by irrigation.
Septic Area: The soils exposed in the Profile Pit are similar to those exposed in the other pits
shown on Figure 2 and consist of sandy loam. Based on the subsurface conditions encountered,
the tested area should be suitable for a conventional infiltration septic disposal system. Once the
septic field loadings are known, we can assist in the design of the infiltration septic disposal
system.
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 submiued in this report are based
upon the data obtained frorn the exploratory pits excavated at the locations indicated on Figure l,
the proposed type of construction and our experience in the area. Our services do not include
detennining 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
Kumar & Associates, lnc. @ Proiect No.23-7-689
-4-
extrapolation of the subsurface eonditions identified at the exploratory pits and variations in the
subsurface conditions may not bec,ome 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 implernentation 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 struch.ual fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of fu*her assistance, please let us know
Respectfu lly Submitted,
K*rnar & A*scaiatem, iln*
Daniel E. Hardin, P
Rev. by: SLP
DEH&ac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figures 3 and 4 - Swell-Consolidation Test Results
Figure 5 - Gradation/Hydrometer Test Results
Table 1 - Summary of Laboratory Test Results
Kumar & A*s**la***, {ne. ::Fr*j*et l,l*. ?3"?"SSs
APPROXIMATE SCALE-FEET
100 o
Fig. 123-7-689 Kumar & Associates LOCATION OF EXPLORTAORY PITS
PIT 1 PIT 2 PROFILE
PIT
0 0
WC=9.5
FLI
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=Fo-
LJo
WC=12.0
DD= 100.4 I GRAVEL=9 F
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SAND=49
Sl LT=28
CLAY= 1 4
5
10 10
LEGEND
TOPSOIL; ORGANIC SANDY CLAY, VERY STIFF/ FROZEN, MOIST, BROWN.
CLAY (CL); SANDY, SILTY, VERY STIFF TO HARD, SLIGHTLY MOIST, BROWN
F
t
HAND DRIVE SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON DECEMBER 7,2023.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PI.AN PROVIDED.
5. 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 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 VVAS 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 (PCt) (ASTU D2216);
GRAVEL = PERCENT RETAINED ON NO. 10 SIEVE;
SAND --=- P,ERCENT- PASSING .NO"-1O-SIEVE AND REIAINED ON NO. 325 -SIEVE-
SILT = PERCENT PASSING NO. 325 SIEVE TO PARTICLE SIZE .002MM;
CLAY= PERCENT SMALLER THAN PARTICLE SIZE .o02MM.
Fig. 223-7 -689 Kumar & Associates LOGS OF EXPLORATORY PITS
SAMPLE OF: Sondy SIlty Cloy
FROMIPltle^2'
WC=9.5%
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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23-7 -689 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23-7-689
SOILTYPE
Sandy Silty Clay
Sandy Silty Clay
Sandy Loam
CIAY
(%)
14
SILT
{%)
28
9.5
49
SAND
f/')
9
USDA SOILTEXTURE
(%)
GRAVELSLT&CLAY
(%)f/"1
SAND
GRADATION
GRAVEL
(%|
NATURAL
DRY
DENSTY
(pcf)
100
NATURAL
MOISTURE
CONTENT
(/"1
12.0-t
3%-6
DEPTH
(ft)
2
SAMPLE LOCATION
PIT
I
2
Profile