HomeMy WebLinkAboutObservation of Excavation 01.02.2018H.PVKUMAR 5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Geotechnical Engineering I Engineering Geology
Materials Testing I Environmental
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
January 2,2OI8
Anna Edgerly
1765 Snowmass Creek Road
Snowmass, Colorado 81654
anna@)binbilla.corn
JAN 1 3 2025
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Project No. l6-7-424
Subject Observation of Excavation, Proposed Barn, I7527 State Highway 82, Garfield
County, Colorado
Dear Ms. Edgerly:
As rcquested by Jason LaPointe with FUSE, a representative of H-P/Kumar observed the
excavation at the subject site on Dccember 29,2A17 to evaluate the soils exposed for foundation
support. The findings of our observations and recommendations for the foundation clesign are
presented in this report. We previously conducted a subsoil study for the proposed residence
foundation design at the site and presented our findings in a report dated October 5,2017, Project
No.16-7-424.
The proposed barn is located in the north, front part of the property. Spread footings placed on
the natural gravcl soils and sized for an allorvable bealing pressurc. of 2,500 psf were designcd
for the barn support.
At the time of our visit to the site, the perimeter footing trench excavation had been cut in one
Ievel about 2r/z feet belor.v the adjacent ground surface. The soils exposed in the bottom of the
excavation consisted of slightly silty sandy gravel and cobbles. No free water was encountered
in the excavation and the soils were slightly moist. Footing forms and rcinforcement steel were
in place at the time of our site visit.
The gravel soils exposed in the excavation are consistent with those previously encountered on
the site and suitable for support of spread footings designed for the rscommended allowable
bearing pressure of 2,500 psf. Loose disturbed soils should be removed in the footing areas to
expose the undisturbed natural soils. The bearing soils should be protected from frost and
concrete should not be placed on frozen soils. Other recommendations presented in our previous
report which are applicable should also be observed.
Anna Edgerly
January 4,2018
PageZ
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation and the previous limited subsurface exploration at the site.
Variations in the subsurface conditions below the excavation could increase the risk of
foundation movement. We should be advised of any variations encountered in the excavation
conditions for possible changes to recommendations contained in this letter. 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 ofpractice should be consulted.
ff you have any questions or need further assistance, please call our office.
Sincerely,
H-P*KUMAR
Steven L. Pawlak, P.E
SLP/kac
cc:FUSE * Jason LaPointe (ilapointe@fuseacs.com)
H-P*KUMAR
Proiect No. '16^7-424
H-PryKUMAR
Geotaehnical Engineering i Enginaering Geology
Materials T€sling I Envirsnmanl*l
5020 county Road't54
GlEnwood Spdngs, CO 81801
PhonE: {970} 945t988
Fax {970) S45'8454
Email: hpkglenwood@kumanrsa,com
Oltice Locatlons: Pa*ar, Glanwood Springs, and Silverthome, Colorado
October 5,2016
Anna Edgerly
1765 $nowmass Creek Road
Snowmoss, Colorado I 1654
(anna@binbilklcorn)
Projert No.l6-7-424
Subject:Subsoil Study for Foundation Design, Proposed Residence, 17527 State Highway
82, Garfield County, Colorado
DearMs. Edgerly:
As requested, H-P/Kumar 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 Septcmber 12,2016. The deta obteined and our recommendations based
on thc proposed construction and subsurface conditions encountered are presented in this report.
The site is adjacent to the Roaring Fork River and we understand flood plain area and elevations
are being addressed by others.
Proposed Construetion: The proposed residence building plans are being developed. We
expect the residence will be one story wood frame construction with an attached garage and
located on the site as shown on Figure l. Ground floor will be slab-on-grnde or above a shallow
crawlspace. Cut depths are expected to range between about I to 3 feet. Foundation loadings for
this type sf 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 property is 4.682 acres and developed with a single family home in the
front (northern) part of the site and a gravel driveway. Vegetation consists of cottonwood trees,
brush, grass and weeds. The ground surface in the area of the proposed residence is relatively
flat with a slight slope down to the northwest. Several inigation ditches cross the site and the
Roaring Fork River is located just south of the building area in the rear of the property. Eagle
Valley Evaporite Formation is exposed on the valley hillsides.
/r
Subsldence Potentialr Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the
lower Roaring Fork Valley. These rocks are a sequence of gypsiferious shale, fine-grained
sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that
massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the
property. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and
can produce areas of localized subsidence. During previous work in the area, several broad
subsidence areas and sinkholes have been observed. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the Roaring Fork Valley.
No evidence of subsidence or sinkholes were observed on the propsrty or encountered in the
subsurface materials, however, the exploratory pits were relatively shallow, for foundation
design only. Based on our prcsent knowledge of the subsurface conditions at the site, it can not
be said for certain that sinkholes will not develop. The risk of future ground subsidence at the
site throughout the service life of the structure, in our opinion is low, however the owner should
be aware of the potential for sinkhole development. If further investigation of possible cavities
in the bEdrock below the site is desired, we should be contacted.
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 one to 3 feet of tapsoil, consist of silty sandy gravel with
cobbles and small boulders. Results of a gradation analysis performed on a sample of sandy
gravel with cobbles (minus 5 inch fraction) obtained from the site are presented on Figure 4.
Free water was observed in the pits at a depth of 4 feet in the building area at the time of
excavation and the upper soils were moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we reccmmend spread footings or a
thickened slab placed on the undisturbed natural granular soil designed for an allowable soil
bearing pressure af 2,500 psf fer support of the proposed residence. Footings should be a
minimum width of 16 inches for continuous walls and 2 feet fior columns. Loose and disturbed
soils and topsoil encountered at the foundation bearing level within the excavaiion should be
removed and the footing bearing level extended down to the undisturbed natural granular 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 area. The site grading and floor level may need to be raised to achieve adequate frost cover.
As an alternative, thickened slab edges or shallsw footings could be frost protected with
insulation in accordance with the lnternational 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 l0 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 45
pcf for the on-site soil as backfill. Due to the groundwater at this site, we recommended that the
main floor be slab-on-grade and crawlspace areas be eliminated.
S'loor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. To reducs the effects of some differential movemenq non-structural
H-P * KUMAR Proiect No. 16-7-424
-3-
floor slabs should be separated from all bearing walls and columns with expansion joints which
allow unrestrained vertical movement. Floor slab cantrol joints should be used to reduce damage
due to shrinkage cracking. The requirements forjoint 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 slabs to facilitate drainage. This material
should consist of minus 2 inch aggregate with less than 507o passing the No, 4 sieve and less
than?Vo pnssing the No.200 sieve.
All fill materials for support of floor slabs should be eompacted to at least 957o 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: For slab-on-grade constructiCIn, if the finished floor elevation at the lowest
level of the residence is at. or above the surounding grade, n foundation drain system is not
required.
$urface Drninage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
l) lnundation 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 leert 95Va af 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 sunounding 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 l0 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.
$eptic Disposal Arear The soil texture and structure conditions in the proposed septic disposal
area were evaluated by excavating one profile pit at the approximate location shown on Figure l.
The log of the profile pit is presented on Figure 2" The subsoils encountered, below about one
foot of topsoil, consist of extremely gravelly sandy loam with cobbles and small boulders.
Results of a gradation analysis performed on a sample of extremely gravelly sand (minus 5 inch
fraction) obtained from thc site are presented on Figure 5. The soil type based on gradation
analysis is 0 due to the rock content. Analysis of the soil texture by feel on the minus No. l0
sieve portion of the soil classifies the soil as sand indicating a soil type l. Free water was
observed in the pit at 3fz feet deep at the time of excavation and the upper soils were moist to
very moist.
Llmitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this Brea at this time. We make no wananty 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 I
and to the depths shown on Figure 2, the proposed type of construction, and our expericnce in
H-PE KUMAR Projoct No. 10-7-424
-4-
the area. Our services do nat include determining the presence, prevention or possibility of mold
orother biological contaminants (MOBC) developing in the future. If thE client is concerned
about MOBC, then a pnrfessional in this spcial 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 implementntion 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 reFresentative of
the geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
H-P*KUMAR
Louis Eller
Reviewed by:
Daniel E. Flardin, P.E.
LEElksw
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Figure 4 - USDA Cradation Test Results
H-P+ KUMAR Project No. 16.7-444
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16-7-424 H-P\KUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1
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TOPSO|b ORGAN|C S|LW SAND W|TH CRAVgt* SOFI, HOIST, DARK ERotyN.
GRAVEL ANO COBBLES
MOTST TO WET, LtcHT -(-cf:9u)i wJT!_ sUAtL BOUI"DERS. SANDY. sLtoHILy sllly, DENSE,
8ROWN, ROUNDED ROCK.
DISTURBED SULK SA}/PIE.
= DEPTH TO WATER ITVEL AT TIME OF EXCAVATING.
NOTES
I. THE EXPLORATORY PITS WERE EXCAVATED WIIH A BACKHOE ON SEPTEUSER 12, 2016.
2. THE LOCATIONS OF THE EXPIORATORY PITS WERE TEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOY'N ON THE SITE PI.AN PROVIDED.
3. TIIE ELEVATIONS OF IHE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORAIORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS SHOULD SE CONSIDERED ACCURATE ONLY TO II{E DEGREE
IMPLIED BY THE METHOD USED.
5, THE LINES BETWEEN IIATEIIAIS SHOWN ON THE EXPLORATORY PIT LOCS REPRESENT THE
APPROXIMATE BOUT{DARIES BE TVEEN MATERIAL TYPES AND THE TRANSINON5 I'AY BE GRADUAI.
6. GROUNDWATER WAS ENCOUNTEREO IN TI{E PITS AT THE TIME OF EXCAVATING. PITS WERE
BACKFILIED SUBSEOUENT TO SAHPI.JNG.
7, I.ABORATORY TEST RESULTS:
+4 = PERCENTAGS RETAINED ON NO. 4 SIEVE
-200 = PERCENTAGE PASSINC N0. 200 SlEvE
GRAVEL= PERCENT RETAINED ON THE No. to
(ASTU D a22);
(AsTlt D lt a0);
SIEVE
SANO
SILT
CLAY
= PERCENT PASSING NO. 10 SIEVE AND RETATNED Oil NO, tZg SIEVE.= PERCENT PAsSlNc NO. 325 SIEVE TO PARTICLE StZg 0.002 MM= PERCENT SUALLER THAN PARTICLE SIZE O.OO2 MM
l6-7-424 *LOGS OF EXPLORATORY PITS Fig. 2
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I]IAMETER OF PANTG|€S IN MILIJMETFRS
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USDA SOIL TYPE: Extremely Graveily Sand FROM: Profile pir 1 @ 3.0-4,
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16-7-424 -P+IruMAR USDA GRADATION TEST RESULTS Fig. +
H-P*KUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 16-7424
SOILTYPE
Sandy Gravel with
Cobbles
Extremely Gravelly
Sard
CLAY
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t%t
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(%)
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DENSITY
(pcD
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DEPTH
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