HomeMy WebLinkAboutSubsoil Study for Foundation Design~tech
HEPWORTH-PAWLAK GEOTECHNICAL
SUBSOIL STUDY
Hepworth-Pawlak Gcotcchnical, Inc .
5020 County Road I 54
Glenwood Springs, Colorado 8160 I
Phone : 970-945-7988
Fax ; 970-945-8454
Email : hpgco@hpgcolcch .com
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 25, SUN MEADOW EST ATES
SOUTH MEADOW DRIVE
GARFIELD COUNTY, COLORADO
JOB NO. 115 056A
MARCH 9, 2015
PREPARED FOR:
KELLY WEST
2410 HOWARD DRIVE
RIFLE, COLORADO 81650
titanficldscrvicc1@gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY .......................................................................... -1 -
PROPOSED CONSTRUCTION .................................................................................. ~ 1 -
SITE CONDITIONS .................................................................................................... -2 -
FIELD EXPLORATION .............................................................................................. -2 -
SUBSURFACE CONDITIONS ................................................................................... ~ 2 -
DESIGN RECOMMENDATIONS ............................................................................... -3 -
FOUNDATIONS ...................................................................................................... -3 -
FLOOR SLABS ....................................................................................................... -4 -
UNDERDRAIN SYSTEM ....................................................................................... :-5 -
SURF ACE DRAINAGE .......................................................................................... ~ 5 -
LIMITATIONS ............................................................................................................ -6 -
FIGURE I -LOCATION OF EXPLORATORY BORlNG
FIGURE 2 -LOG OF EXP LORA TORY BORING
FIGURE 3 -LEGEND AND NOTES
FIGURE 4 -SWELL-CONSOLIDATION TEST RES UL TS
TABLE I -SUMMARY OF LABOROATRY TEST RESULTS
PURPOSEANDSCOPEOFSTUDY
This report presents the results of a subsoil study for a proposed residence to be located
on Lot 25, Sun Meadow Estates, South Meadow Drive, 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 a!:,rreement for geotechnical engineering services to Kelly West dated February
19, 2015. Hepworth-Pawlak Geotechnical Inc., previously performed a preliminary
geotechnical study for Sun Meadow Estates (formerly Mamms View) and presented our
findings, in a report, dated March 28, 2000, Job No. l 00 169.
A field exploration pr0!:,1fam consisting of one exploratory boring located in the
designated building area 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.
PROPOSED CONSTRUCTION
The proposed residence will be single story wood frame construction above a crawlspace
in the living and have an attached garage with slab-on-grade floor. Grading for the
structure is assumed to be relatively minor with cut depths between about 2 to 5 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.
Job No. 115 056A ~tech
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SITE CONDITIONS
Lot 25 is located on the southwest comer of South Meadow Drive and Antonelli Lane and
was vacant at the time of our field visit. The lot is bordered to the west and south by Lots
26 and 33. The building area designated to us by the client is located in the south part of
the lot. Vegetation consists of grass and weeds. The ground surface in the building area is
relatively flat with a gentle slope down to the southwest.
FIELD EXPLORATION
The field exploration for the project was conducted on February 20, 2015. One
exploratory boring was drilled in the designated building area at the approximate location
shown on Figure 1. The exploratory boring was advanced with 4-inch diameter
continuous flight augers powered by a truck-mounted CME-458 drill rig. The boring was
logged by a representative of Hepworth-Pawlak Geotechnical, Inc.
Samples of the subsoils were taken with a 2 inch l.D. spoon sampler. The sampler was
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 one foot of topsoil, consist of very stiff to hard sandy clay
down to about I 0 feet overlying silty to clayey sand with gravel and scattered cobbles and
sandy silt layers to the depth explored of 26 feet.
Laboratory testing perfonned on samples obtained from the boring included natural
moisture content and density and finer than sand size gradation. Results of swell-
consolidation testing performed on relatively undisturbed drive samples of the clay soils,
Job No . 115 056A
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presented on Figure 4, indicate low compressibility under conditions of light loading and
existing moisture conditions with a low to moderate swell potential when wetted. The
laboratory testing is summarized in Table l.
No free water was encountered in the boring at the time of drilling and the subsoils were
slightly moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
The clay soils are expansive when wetted and could heave lightly loaded footings and
slabs-on-grade. The settlcmenVheavc potential should be further evaluated at the time of
construction. Considering the subsurface conditions encountered in the exploratory
boring, the nature of the proposed construction and the soils typical of this area, the
building can be designed with spread footings bearing on the natural soils with a risk of
movement mainly from wetting of the bearing soils. If the soils exposed at bearing level
are expansive, subexcavation and replacement with non-expansive structural fill or
designing the footings for a minimum dead load could be needed and should be further
evaluated at the time of construction.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
I) Footings placed on the undisturbed natural soils with low to no expansion
potential should be designed for an allowable bearing pressure of 1,500
psf. Based on experience, we expect initial settlement of footings
designed and constructed as discussed in this section will be about 1 inch
or less. There could be additional differential movement of about 1 inch if
the bearing soils become wetted depending on the results of additional
footing bearing soil evaluation.
2) The footings should have a minimum width of 16 inches for continuous
walls and 2 feet for isolated pads.
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3) Exterior footings and footings beneath unheated areas 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.
4) Continuous foundation walls should be reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12
feet. Foundation walls acting as retaining structures should also be
designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least 55 pcf.
5 ) The topsoil and any loose or disturbed soils should be removed and the
footing bearing level extended down to the undisturbed natural soils. The
exposed soils should be evaluated for expansion potential. If they show
moderate to high expansion potential, at least 3 feet of non-expansive
structural fill, such as road base, compacted to at least 95% of standard
Proctor density should be provided below footing areas.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing c onditions.
FLOOR SLABS
The natural clay soils are expansive and there could be some heave of slabs-on-brrade.
Non-expansive structural fill could be needed below slabs to help reduce the heave
potential. 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 compac ted to at least 95 % of
maximum standard Proctor density at a moisture content near optimum. Required fill
should consist of imported granular soils d e void of vegetation and topsoil.
Job No. 11 5 056A ~ech
UNDERDRAJN 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 runoff can create a perched
condition. We recommend below-grade construction, such as retaining walls and
crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an
underdrain system. An underdrain should not be needed around the crawlspace provided
foundation wall backfill is well compacted and the surface has a positive slope away from
the building as described below in the SURF A CE DRAIN A GE section.
Where drains are installed, they 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 finish !:,'fade and sloped at a minimum I% to a suitable &rravity outlet or sump
and pump. 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 1 Yi feet deep.
SURF ACE DRAINAGE
The following drainage precautions should be observed during construction and
maintained at all times after the residence has been completed:
I) 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
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recommend a minimum slope of 12 inches in the first I 0 feet in unpaved
areas and a minimum slope of 3 inches in the first l 0 feet in paved areas .
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 I, 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 of excavations and foundation
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bearing strata and testing of structural fill by a representative of the geotechnical
engineer.
Respectfully Submitted,
HEPWORTH -PAWLAK GEOTECHNICAL, INC.
Steven L. Pawlak , P.E.
Reviewed by:
SLP/ksw
Job No. 115 056A ~ech
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LOT 26
115 056A
ANTON ELLI LANE (CR 216)
LOT33
LOT 25
BORING 1
•
~
Hl!:l'WORTI+PAWl.AK GEon:CHNICAL
/
I
APPROXIMATE SCALE
1 = 60'
LOCATION OF EXPLORATORY BORING Figure 1
.. . .
BORING 1
0 0
7/6, 10/6
45/12
WC =57
5 00 .. 117 5 29/12
WC 53
DD 117
-200 -61
10 20/12 10
WC =36
00=109
-200 ;;67
Q) Q)
Q) Q)
LL 15 15 LL
60/6 I
.s:; .s:; a. a.
Q) Q)
Cl Cl
20 20/12 20
25 20/12 25
30 30
NOTE : Explanation of symbols is shown on Figure 3.
115 056A ~
He worth-Powlak Geotechnlcal
LOG OF EXPLORATORY BORING Figure 2
LEGEND:
TOPSOIL; organic sandy silt and clay, dark brown.
CLAY (CL); silty, sandy, very stiff to hard, slightly moist, light brown. low to medium plasticity, light to moderate
calcareous.
SAND (SM -SC); silty, clayey, gravelly, scattered cobbles, some sand sill lenses, medium dense, slightly moist.
light brown.
Relatively undisturbed drive sample; 2-inch 1.0. California liner sample.
Drive sample blow count ; indicates that 45 blows of a 140 pound hammer falling 30 inches were
45/12 required to drive the California sampler 12 inches.
NOTES:
1. The exploratory boring was drilled on February 24, 2015 with a 4-inch diameter continuous flight power auger.
2. The exploratory boring was located from site features and within area of building corner stakes .
3. The exploratory boring elevation was not measured and the log of exploratory boring is drawn to depth .
4. The exploratory boring location and elevation should be considered accurate on ly 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 transitions may be gradual.
6. No free water was encountered in the boring at the time of drilling. Fluctuation in water level may occur with time .
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pcf)
-200 = Percent passing No. 200 sieve
115 056A ~
HEPWOltTH·PAWLAK GttOTECHNICAL
LEGEND AND NOTES Figure 3
..
Moisture Content = 5.7 percent
Dry Density =: 117 pcf
Sample of : Silty Sandy Clay, Calcareous
From: Boring 1 at 3 Feet
2
~
c 0 1 I '---
'ii) -1---c c: )........_ <O ' a. ~ po.._ x w 0
I ·~ ' .... c:
0 -,
'(ii ~~ Cl)
Q.l 1 ....
Expansion a.
E 0 upon
(.) wetting 2
0.1 1.0 10 100
APPLIED PRESSURE -ksf
Moisture Content = 5.3 percent
Dry Density "" 117 pcf
Sample of : Very Sandy Clay
From : Boring 1 at 5 Fee t
2
~
c:
0 1 'iii c:
"'
co a. x ~} UJ
I 0 c: '\ ....... 0
'ii) ~~ Cl)
Q.l .... 1 a.
E Expansion 0
(.) upon
2 wetting
0.1 1.0 10 100
APPLIED PRESSURE -ksf
115 056A ~
Hepworth-Powlok Geotechnleol
SWELL-CONSOLIDATION TEST RESULTS Figure 4
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 Job No. 115 056A
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL GRADATION ATIERBERG LIMITS UNCONFINED
MOISTURE NATURAL GRAVEL SAND PERCENT COMPRESSIVE PLASTIC SOIL OR BORING DEPTH CONTENT DRY DENSITY PASSING NO. LIQUID LIMIT STRENGTH (%) (%) 200 SIEVE INDEX BEDROCK TYPE
(hi f%) (pcf) {%) (%) {PSF)
I 3 5.7 117 Silty Sandy Clay, Calcareous
5 5.3 117 Very Sandy Clay
IO 3.6 109 67 Very Sandy Silt