HomeMy WebLinkAboutSoils Report 06.30.2017H-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: Parker, Glenwood Springs, and Silverthorne, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 72, IRONBRIDGE
1219 RIVER BEND WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-423
JUNE 30, 2017
PREPARED FOR:
CHRISTOPHER REED
26304 REYGLEN DRIVE
SAN ANTONIO, TEXAS 78255
(reed-chris @ att.net)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION. - 1 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 3 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 4 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS 6 -
NONSTRUCTURAL FLOOR SLABS - 7 -
UNDERDRAIN SYSTEM - 7 -
SURFACE DRAINAGE - 8 -
LIMITATIONS - 8 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-423
W-PkKUMAR
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
72, Ironbridge, 1219 River Bend Way, 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 Christopher Reed dated May 24, 2017. Hepworth-Pawlak Geotechnical, Inc.
previously conducted geotechnical engineering studies for the subdivision development, reports
dated October 29, 1997 and February 12, 1998, Job No. 197 327, and for Lot 72 in 2007.
An exploratory boring was drilled 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.
PROPOSED CONSTRUCTION
The proposed residence will be one story wood frame construction with an attached garage and
located approximately as shown on Figure 1. Ground floor will be slab -on -grade. Grading for
the structure is assumed to be relatively minor with cut depths between about 2 to 3 feet. We
assume relatively light foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
H-P3/4KUMAR
Project No. 17-7-423
-2 -
SITE CONDITIONS
The site is located on an alluvial fan along the uphill, western side of River Bend Way. The lot
was vacant at the time of our field exploration. Vegetation consists of grass and weeds. The site
had been graded during subdivision development with shallow cuts and fill. The ground surface
is relatively flat with a slight slope down to the east. The slope steepens on the west side of the
lot. The Robertson Ditch is piped in an easement uphill and behind the lot.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Ironbridge Subdivision.
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 development, several sinkholes have been
observed. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in
areas of the Roaring Fork River valley.
No evidence of subsidence or sinkholes was observed on the property or encountered in the
subsurface materials, however, the exploratory borings were relatively shallow, for foundation
design only. The nearest mapped sinkholes to Lot 72 are located about 700 feet northwest and
900 feet south. These sinkholes were mitigated by backfilling and grouting the cavities and
disturbed soils down to hard bedrock. Based on our present 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.
H-P-KUMAR
Project No. 17-7-423
-3 -
FIELD EXPLORATION
The field exploration for the project was conducted on June 9, 2017. One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
was advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted CME -
45B drill rig. The boring was logged by a representative of H-P/Kumar. Location of the
exploratory boring drilled for the 2007 subsoil study is also shown on Figure 1.
Samples of the subsoils were taken with 1% 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, below about 31 feet of fill, consist of medium dense, silty sand and gravel to 14 feet
and interlayered silty sand and sandy silt to 25 feet (alluvial fan deposit) overlying relatively
dense, sandy gravel with cobbles and boulders (river gravel alluvium). Drilling in the dense
granular soils with auger equipment was difficult due to the cobbles and boulders and drilling
refusal was encountered in the deposit at 28 feet. The subsoil profile is similar to that
encountered in the 2007 subsoil study.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density, and gradation analyses. Results of swell -consolidation testing performed on
a relatively undisturbed drive sample of the silt and sand soil, presented on Figure 3, indicate low
compressibility under natural moisture condition and light loading and moderate collapse
potential (settlement under constant load) when wetted. Results of gradation analyses performed
H -N KUMAR
Project No. 17-7-423
-4 -
on a small diameter drive sample (minus 11/ inch fraction) of the upper silty sand and gravel
soils are shown on Figure 4. 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.
FOUNDATION BEARING CONDITIONS
The upper debris fan deposit soils typically have low bearing capacity and low to moderate
settlement potential when wetted under loading and extend down about 20 feet below a shallow
foundation such as spread footings. Considering the compressible nature of the debris fan soils
and the potential for wetting from landscape irrigation or other sources, spread footings could
have a high risk of excessive settlement and are not recommended for the building foundation
support.
With a risk of differential settlement and minor distress, the building could be founded
with a heavily reinforced structural (mat) slab or post -tensioned slab foundation bearing on at
least 3 feet of compacted structural fill and is recommended for the building support.
As an
alternative, foundations that extend down to the dense, river gravel alluvium (such as piers or
piles) could be used and would have moderate bearing capacity with low settlement potential and
building distress risk.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, the building can be founded with a heavily reinforced structural slab
foundation bearing on compacted structural fill and the underlying natural soils. If a deep
foundation system is considered for building support, we should be contacted for additional
recommendations.
H-P7,
Project No. 17-7-423
structural fill should be designed for an allowable bearing pressure of 1,500 psf or
-5 -
The design and construction criteria presented below should be observed for a heavily reinforced
structural slab or post -tensioned slab foundation system.
1)
A heavily reinforced structural slab or post -tensioned slab placed on compacted
for a subgrade modulus of 100 tcf. The post -tensioned slab placed on structural
fill should be designed for a wetted distance of 10 feet or at least half of the slab
width, whichever is greater. Initial settlement of the foundation is estimated to be
about 1 inch. Additional settlement of about 1 to 2 inches is estimated if deep
wetting of the debris fan soils were to occur.
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, if any, 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 be removed. Additional
structural fill placed below the slab should be compacted to at least 98% of the
maximum Proctor Density within 2 percentage points of the 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
to evaluate bearing conditions.
H-P-KUMAR
Project No. 17-7-423
-6 -
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 since 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 residence and 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.
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 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
H-P-KUMAR
Project No. 17-7-423
-7 -
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 a compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
NONSTRUCTURAL FLOOR SLABS
Compacted structural fill can be used to support lightly loaded slab -on -grade construction
separate from the building foundation. The fill and debris fan soils can be compressible when
wetted and can result in some post -construction settlement. To reduce the effects of some
differential movement, nonstructural floor slabs should be separated from buildings to 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. A minimum 4 -inch
layer of relatively well -graded sand and gravel, such as road base, should be placed beneath slabs
as subgrade support. 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 soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
It is our understanding the finished floor elevation of the residence at the lowest level is at or
above the surrounding grade. Therefore, a foundation drain system is not required. 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 runoff can create a perched
condition. We recommend below -grade construction, such as retaining walls, be protected from
wetting and hydrostatic pressure buildup by an underdrain and wall drain system.
H-PtiKUMAR
Project No. 17-7-423
If the finished floor elevation of the proposed structure has a floor level below the surrounding
grade, we should be contacted to provide recommendations for an underdrain system. All earth
retaining structures should be properly drained.
SURFACE DRAINAGE
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 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3
inches in the first 10 feet in paved areas. Graded swales should have a minimum
slope of 3%.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation 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
H-P�KUMAR
Project No. 17-7-423
-9 -
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 niay 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
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
W-PKU MAR
�`. U 0.1
Steven L. Pawlak, P.E.' x
�'. i 6/5 /Mid 7
Reviewed by: } ; gip'''„ Cr�g7,;,'
Daniel E. Hardin, P.E.
SLP/ksw
cc: RM Construction — Blake Piland (bbake@buildwithrm.com)
H-PkKUMAR
Project No. 17-7-423
411
LEGEND:
BORING DRILLED FOR THIS
STUDY.
® BORING DRILLED FOR
PREVIOUS STUDY DATED 2007.
0
5
10
aL
w
— 20
-- 25
30
17-7-423
BORING 1
10/6, 40/3
WC=12.7
DD=111
— 200=72
LEGEND
FILL: SILTY SAND AND GRAVEL WITH COBBLES, MEDIUM DENSE, MOIST,
MIXED BROWN.
pSAND AND GRAVEL (SM—GM); SILTY, MEDIUM DENSE, SLIGHTLY MOIST,
BROWN.
SILT AND SAND (ML—SM); INTERLAYERED SILTY SAND AND SANDY SILT,
17/12 CLAYEY, SCATTERED GRAVEL, SLIGHTLY MOIST TO MOIST WITH DEPTH,
• BROWN.
GRAVEL (GM—GP); WITH COBBLES AND BOULDERS, SANDY, SILTY,
DENSE, MOIST, LIGHT BROWN, ROUNDED ROCK.
35/12
WC=2.2
+4=48
—200=14
22/12
WC=4.8
D0=102
10/12
WC=22.3
DD=102
— 200=87
77/12
DRIVE SAMPLE, 2—INCH I.O. CALIFORNIA LINER SAMPLE.
] DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION
TEST.
17/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 17 BLOWS OF A
140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE
THE SAMPLER 12 INCHES.
--tt- DEPTH AT WHICH BORING CAVED.
4 PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORING WAS DRILLED ON JUNE 9, 2017 WITH A
4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN
PROVIDED.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT MEASURED
AND THE LOG OF THE EXPLORATORY BORING IS PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED
ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY
BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN
MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME
OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pci) (ASTM 0 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
H-PvKUMAR
LOG OF EXPLORATORY BORING
Fig. 2
SAMPLE OF: Clayey Silt and Sand with
Gravel
FROM: Boring 1 @ 15'
WC = 4.8 %, 00 = 102 pcf
TE.rr trri Rwnr apply onty W Nr
.WApf.A I.,.d. i2. tomtinp mere
.110 nal b rweduecd, r.e pt in
bRhoul w rdllen alA10..1 of
Rumor end Pira Elea, Nr. SrNI
C,anaogdolloA Wit/14 Cr+fo,m d is
eeccfianee n!M1 115Th 0-4517.
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
17-7-423
10 APPLIED PRESSURE —
H-P-~KUMAR
KSF
10. 100
SWELL -CONSOLIDATION TEST RESULTS
Fig. 3
HYGROMETER ANALYSIS SIEVE ANALYSIS
100
74 NRS
45 mai
7 NRO
10 min 50Ya1
TIME REAOINC5
INU15. aM9f,
;200
;No
U.5.
/50
Ll•AMIWu10
;f0 ;la
1
:moms
;
S 010
1_
da pR
I
A/p"
CLEAR
3/4"
6aVA1EE
•1.-•
OPENINGS
A. -._'_5'e"
90
-
_ ._...
_
.
__..
—.
..
T—I...
1a
t
_
_._
-.—t-
-r_-
1
1
30
-
.. .
— _.
--;_
_.:"__
--. —
..
20
-
---.__
t�-T-`
--
--_-
--•=I
t.
a0
T
_ ,. .. ._
1090
_.
I__
._.__
_
...
— ....
...
_
.
_l
—_
a
- . -
3- 1
J...im_t_
-.
t..--1
.1..L_E1•flJ
It l
IT T
I..
.1-=1.ln_MIL.�.:j
---1—r—I J.1i1--
lag
.001 .002 .603 .009
__A
.019 .057 .076 .160 .105 1 .690 1.
.426
DIAMETER OF PARTICLES IN MILOMETERS
a 1 2.35 4.78 Y 6 19
2.0
31.1 76. 12/
132
CLAY TO SILT
SA ND
GRAVEL
FINE MEDIUM
MEDIUM COARSE
FINE
COBBLES
GRAVEL 4B 5: SAND 38 Y. SILT AND CLAY 14 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Silty Sand and Gravel FROM: Boring 1 ® 10'
These feel resulla apppty eery t0 the
s101pl►s whkh were felted. The
telling report &hall not he reproduced.
except In foll, wllhaut !he written
approval of Kumcr & Assoclolsa, Inc.
Slew analysts feeling 1e p&rfermsd to
0cc0rdanco with ASTM 6422. ASTM C136
and/or ASTM 01140,
17-7-423
H -P KUlAR
GRADATION TEST RESULTS
Fig. 4
H P
(UN/
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-423
SAMPLE LOCATION INATURAL
GRADATION
ATTERBERG LIMITS
UNCONFINED
BORING
DEPTH
(ft)
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pof)
GRAVEL
C/0)
SAND
(%)
PERCENT
PASSING '
NO. 200
SIEVE
LIQUID
LIMIT
(%)
PLASTIC
i INDEX
(%)
COMPRESSIVE
STRENGTH
(PSF)
SOIL
1
21/2
12.7 111
72
Sandy Silt and Clay with
Gravel - Fill
10
2.2
48
38
14
Silty Sand and Gravel
15
4.8
102
Clayey Silt and Sand with
Gravel
20
22.3
102
87
Sandy Silt