HomeMy WebLinkAboutSoils Report 01.17.2018H-P�KUMAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 251, IRONBRIDGE
EAGLE CLAW CIRCLE
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-866
JANUARY 17, 2018
PREPARED FOR:
MIKE DEER
P. O. BOX 2090
GLENWOOD SPRINGS, COLORADO 81602
mikedeer@sooris.net
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
BACKGROUND INFORMATION - 1
PROPOSED CONSTRUCTION - 1
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
ENGINEERING ANALYSIS _ 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
NONSTRUCTURAL FLOOR SLABS - 7 -
UNDERDRAIN SYSTEM 7 -
SITE GRADING _ g -
SURFACE DRAINAGE - 8 -
LIMITATIONS - 9 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
H-P%KUMAR
Project No. 17-7-866
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
251, Ironbridge, Eagle Claw Circle, Garfield County, Colorado. The project site is shown on
Figure 1. The purpose of the study was to develop recommendations for the foundation design.
The study was conducted in accordance with our agreement for geotechnical engineering
services to Mike Deer dated December 11, 2017. We previously conducted a preliminary subsoil
study for residences in the Villas North and Villas South parcels of Ironbridge and presented our
findings in a report dated February 28, 2014, Job No. 113 471A.
A field exploration program consisting of an exploratory boring was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzed to develop recommendations for foundation types, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conclusions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
BACKGROUND INFORMATION
The proposed residence is located in the existing Ironbridge subdivision development.
Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously conducted subsurface exploration
and geotechnical evaluation for development of Villas North and Villas South parcels, Job No.
105 115-6, report dated September 14, 2005, and performed observation and testing services
during the infrastructure construction, Job No. 106 0367, between April 2006 and April 2007.
The information provided in the previous reports has been considered in the current study of Lot
251.
PROPOSED CONSTRUCTION
Development plans for the lot were not available at the time of our study. The proposed
residence is assumed to be a two-story wood frame structure with a structural slab foundation
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and no basement or crawl -space. A post -tensioned slab foundation has been used to support the
existing residences in this area. Grading for the structure is assumed to be relatively minor with
cut and fill depths on the order of a few feet or less. We assume relatively light foundation
loadings, typical of the proposed type of construction.
When the building loadings, location and grading plans have been developed, we should be
notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The proposed residence is located on the west side of the Villas South parcel overlooking the
18th Green. The natural terrain prior to development in 2006 sloped down to the east at about 5 to
7% grade. The subdivision in this area was elevated by filling on the order of 15 to 20 feet
above the original ground surface to create a relatively level building site with a moderate slope
down along the west side to the 18th Green. Vegetation consists of grass and weeds.
SUBSIDENCE POTENTIAL.
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. These rocks
are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds
of gypsum and limestone. The Eagle Valley Evaporite is known to be associated with sinkholes
and localized ground subsidence in the Roaring Fork River valley. A sinkhole opened in the cart
storage parking lot east of the Pro Shop located to the north of the Villas South parcel in January
2005. Other irregular bedrock conditions have been identified in the affordable housing site
located to the west of the Villas North parcel. Indications of ground subsidence were not
observed in the Villas development area that could indicate an unusual risk of ground
subsidence, but localized variable depths of the debris fan soils encountered in the previous
September 14, 2005 geotechnical study in the Villas development area could be the result of past
subsidence. In our opinion, the risk of future ground subsidence in the Villas North and South
project area is low and similar to other areas of the Roaring Fork River valley where there have
not been indications of ground subsidence.
FIELD EXPLORATION
The field exploration for the project was conducted on December 27, 2017. One exploratory
boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The
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boring was advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted
CME -45B drill rig and was logged by a representative of H-P/Kumar.
Samples of the subsoils were taken with 1'/8 inch and 2 -inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140 -pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about 6 inches of topsoil overlying around 15 feet of mixed sand, silt, and
clay with gravel man placed fill. Slightly sandy to sandy silt with lenses and layers of gravel was
encountered at depths from 15 to 50 feet. At a depth of 50 feet, very dense rounded gravel and
cobbles (river gravel alluvium) was encountered.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and percent finer than sand size gradation analyses. Results of swell -consolidation
testing performed on a relatively undisturbed drive sample of the natural sandy silt soils,
presented on Figure 3, indicates low to moderate compressibility under light loading and a low
collapse potential (settlement under load) when wetted. The laboratory testing is summarized in
Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist to moist.
ENGINEERING ANALYSIS
The upper 15 feet of soils encountered in the boring consist of fill placed mainly in 2006 as part
of the subdivision development. The field penetration tests and laboratory tests performed
during the study, and review of the field density tests performed during the fill construction
indicate that the structural fill was placed and compacted to the project specified 95% standard
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Proctor density. Debris fan soils which tend to collapse (settle under constant load) when wetted
were encountered below the fill. The amount of settlement will depend on the thickness of the
compressible soils and their wetted depth. The settlement potential and risk of excessive
building distress can be reduced by compaction of the soils to a certain depth below the
foundation bearing level (as has already been done) and by heavily reinforcing the foundation to
resist differential settlements. The compaction should also extend beyond to below driveway
and utility areas. The compacted soils can consist of the existing structural fill used to elevate
the project site. Foundation levels deeper than 5 feet below the existing ground surface on this
site are not recommended.
Relatively deep structural fills will also have some potential for long
term settlement. Proper grading, drainage, and compaction as presented below in the Site
Grading and Surface Drainage sections will help reduce the settlement risks. A heavily
reinforced structural slab or post -tensioned slab foundation designed for significant differential
settlements is recommended for the building support.
As an alternative, a deep foundation that
extends down into the underlying dense, river gravel alluvium and structural floor slabs could
also be used to reduce the settlement risk.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with a heavily reinforced
structural slab or post -tensioned slab foundation bearing on at least 15 feet of compacted
structural fill in the Villas South parcel. If a deep foundation system is considered for building
support, we should be contacted for additional recommendations.
The design and construction criteria presented below should be observed for a structural or post -
tensioned slab foundation system.
1) A structural slab or post -tensioned slab placed on at least 15 feet of compacted
structural fill should be designed for an allowable bearing pressure of 1,500 psf.
Post -tensioned slabs placed on structural fill should be designed for a wetted
distance of 10 feet but at least half of the slab width, whichever is more.
Settlement of the foundation is estimated to be about 1 to 11/ inches based on the
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long-term compressibility of the fill. Additional settlement between about 2 to 3
inches is estimated if deep wetting of the debris fan soils were to occur.
Settlement from the deep wetting would tend to be uniform across the
building/development area and the settlement potential of the fill section should
control the design.
2) The thickened sections of the slab for support of concentrated loads should have a
minimum width of 20 inches.
3) The perimeter turn -down section of the slab should be provided with adequate soil
cover above their bearing elevation for frost protection. Placement of foundations
at least 36 inches below exterior grade is typically used in this area. If a frost
protected foundation is used. The perimeter turn -down section should have at
least 18 inches of soil cover.
4) The foundation should be constructed in a "box -like" configuration rather than
with irregular extensions which can settle differentially to the main building area.
The foundation walls, where provided, should be heavily reinforced top and
bottom to span local anomalies such as by assuming an unsupported length of at
least 14 feet. Foundation walls acting as retaining structures should also be
designed to resist lateral earth pressures as discussed in the "Foundation and
Retaining Walls" section of this report.
5) The root zone and any loose or disturbed soils should he removed. Structural fill
placed below the slab bearing level should be compacted to 98% of the maximum
standard Proctor density within 2 percentage points of optimum moisture content.
6) A representative of the geotechnical engineer should evaluate the compaction of
the fill materials and observe all footing excavations prior to concrete placement
for bearing conditions.
FOUNDATION AND RETAINING WALLS
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 soils. Cantilevered retaining structures which are separate from the building and
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can be expected to deflect sufficiently to mobilize the full 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 soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls. Site walls with a
maximum back slope of 2 horizontal to 1 vertical should be designed for an active earth pressure
of at least 60 pcf equivalent fluid unit weight.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at least 95% of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 300 pcf. The
coefficient of friction and passive pressure 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. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
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Project No. 17-7-866
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NONSTRUCTURAL FLOOR SLABS
Compacted structural fill can be used to support lightly loaded slabs -on -grade separate from the
building foundation. The fill soils can be compressible when wetted and result in some post -
construction settlement. To reduce the effects of some differential movement, nonstructural
floor slabs should be separated from buildings to allow for 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 relatively well
graded sand and gravel, such as road base, should be placed beneath slabs to facilitate drainage.
This material should consist of minus 2 -inch aggregate with at least 50% retained on the No. 4
sieve and less than 12% 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 fill can consist of the on-
site granular 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
mountainous areas that 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 -grade construction, such as grade change site retaining walls,
be protected from wetting and hydrostatic pressure buildup by an underdrain system. An
underdrain should not be provided around structural building foundation slabs and separate
slabs -on -grade
Where installed, 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 1 foot below lowest adjacent finish grade and
sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the
underdrain system should contain less than 2% 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 11/2 feet deep.
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Project No. 17-7-866
8
SITE GRADING
Extensive grading was performed as part of the existing Villas South development. Additional
placement and compaction of the debris fan soils could be needed to elevate the site to design
grades and reduce the risk of excessive differential settlements and building distress. In addition.
The water and sewer pipe joints should be mechanically restrained to reduce the risk of joint
separation in the event of excessive differential settlement. Additional structural fill placed
below foundation bearing level should be compacted to at least 98% of the maximum standard
Proctor density within 2 percentage points of optimum moisture content. Prior to fill placement,
the subgrade should be carefully prepared by removing any vegetation and organic soils and
compacting to at least 95% of the maximum standard Proctor density at near optimum moisture
content. The fill should be benched into slopes that exceed 20% grade.
Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter
and protected against erosion by revegetation or other means. This office should review site
grading plans for the project prior to construction.
SURFACE DRAINAGE
Precautions to prevent wetting of the bearing soils, such as proper backfill construction, positive
backfill slopes, restriction landscape irrigation, and use of roof gutters need to be taken to help
limit settlement and building distress. The following drainage precautions should be observed
during construction and maintained at all times after the residence has been completed:
1) Inundation of the 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 95% 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.
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 5 feet in unpaved areas and a minimum slope of 3
inches in the first 10 feet in paved areas. Free -draining wall backfill should be
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capped with about 2 feet of the on-site soils to reduce surface water infiltration.
Surface swales in landscape areas should have a minimum grade of 4%.
4) Roof gutters should be provided with downspouts that discharge at least 5 feet
beyond the foundation and preferably into subsurface solid drain pipe.
5) Landscaping which requires regular heavy irrigation, such as sod, should be
located at least 10 feet from foundation walls. Consideration should be given to
use of xeriscape to reduce the potential for wetting of soils below the building
caused by irrigation.
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 submitted in this report are based upon the data obtained
from the exploratory boring drilled at the location indicated on Figure 1, 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 boring 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 so
that 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 implementation 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
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of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
H -P= KUMAR
Robert L. Duran, E. I.
Reviewed by:
a
Steven L. Pawlak,
RLD/kac
H-P*KUMAR
Project No. 17-7-866
3
BORING 1
LOT 251
40473 SF.
0.0931 AC.
A -pjA
S n SLAT
L. LSA'
ie. SSIbC{PE
C Lir
C0‘IN t
s,� _- 4
alp
Are
15 O 15 30
APPROXIMATE SCALE -FEET
Lor LACE
MACAO
LOT 254
42893 S.F.
0.099} AC.
17-7-866 H-p--KUMAR
LOCATION OF EXPLORATORY BORING ] Fig. 1
DEPTH -FEET
1'^ 0
— 5
— 10
— 15
20
25
— 30
— 35
40
--- 45
---- 50
— 55
— - 60
BORING 1
EL. 5995'
50/5
79/12
05=7.6
00=113
- 200=B6
30/12
21/12
WC=3.3
05=130
- 200=15
28/12
WC=5.0
00=111
46/12
25/12
WC=5.2
05=111
- 200=66
57/12
50/3
LEGEND
I�.,.
TOPSOIL; CLAY AND SILT, SANDY, FIRM, SLIGHTLY M015T, BROWN,
SLIC111LY O8509115.
FILL; 511.T AND SAND, CLAYEY, SCATTERED GRAVEL AND SANDSTONE
FRAGMENTS, HARD, SUGHTLY M0W, TAH.
SILT WITH GRAVEL LENSES (GM -ML}; SLIGHTLY SA40Y TO SANDY,
VERY STIFF TO HARD/MEDIUM 65009 TO DENSE, SLIGHTLY MOIST,
DROWN, SCATTERED COBBLES.
ROUNDED GRAVEL AND COBBLES (GP -GM); PROBABLE BOULDERS,
, SILTY, SANDY, VERY DENSE, BROWN.
111 DRIVE SAMPLE, 2-1659 I.O. CALIFORNIA LINER SAMPLE.
IDRIVE SAMPLE, 1 3/8 -INCH I.D. SPLIT SPOON STANDARD
PENETRAIIQN TEST,
50/5 DRIVE SAMPLE BLOW COUNT, 119095 TFS THAT 50 BLOWS OF
A 140 -POUND 1169016 FALUHO 30 INCHES WERE REQUIRED
TO DRIVE T115 SAMPLER 5 INCHES.
NOTES
I. THE EXPLORATORY 008190 WAS DRILLED ON DECEMBER 27, 2017
WITH A 4-I9511 DIAOElER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY 80RING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE
PUN PROVROEO.
3. THE ELEVATION of THE EXPLORATORY BORING WAS 000416ED 8Y
INTERPOLATION BETWEEN CONTOURS ON THE SUBDIVISION PLAN.
4. THE 53950RATORY BORING LOCATION AND ELEVATION SHOULD BE
CONSIDERED ACCURATE ONLY 70 THE DEGREE IMPLIED BY THE
151900 65E0.
5. THE UNES BETWEEN MATERIALS 51109N 011 ME EXPLORATORY
BORING LOG REPRESENT TH5 APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRAH5161005 MAY BE ORAOUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME
OF DRILUNG.
7. LABORATORY TEST RESULTS:
WC = WATER CQHTEHT (x) OM 0 2216);
0D = DRY DENSITY (PCA (ASTM 0 2216);
-200 = PERCENTAGE PASSING 60. 200 SIEVE (ASTM 0 1140).
LOG OF EXPLORATORY BORING
CO
CO
1
sr
E.
gra
SAMPLE OF: Sandy Silt with Gravel
FROM: Boring 1 ® 20'
WC = 5.0 %, DD = 111 pcf
Thier t,I ri+;li.Ip$.e y So 11w
♦omprH tested The lest ep mood
O NO not he wprodeced, 4lxe0e in
..then 4 the wr;ti.e approval of
K vmq' PRI RafoClate,, Me Swell
CeMG ddlien OrImp prfunnimi in
OrCar4ance with ASN [I -4,1
1.0 APPLIED PRESSURE - KSF 10
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
r
100
7-7-866
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SWELL—CONSOLIDATION TEST RESULTS
Fig. 3
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-866
SAMPLE LOCATION
NATURAL NATURAL
GRADATION ATTERBERG LIMITS
PERCENT UNCONFINED
BORING DEPTH MOISTURE DRY GRAVEL SAND PASSING I LIQUID ! PLASTIC COMPRESSIVE
CONTENT DENSITY (%) (%) NO. 200 LIMIT I INDEX STRENGTH j ,
(f) 4`v} C ale oho PS
SIEVE
1 5 7.6 113 88
15 3.3 130
15
I 20 5.0 111
30 5.2 111
66
SOIL TYPE
Fine Sand and Silt (Fill)
Sandy Silt and Gravel
Sandy Silt with Gravel
Sandy Silt
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