HomeMy WebLinkAboutSoils Report.pdfSUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED ADDITON TO EXISTING HOUSE
AND RV STORAGE/GREENHOUSE STRUCTURE
2621 COUNTY ROAD 100
CARBONDALE, COLORADO 81623
JOB NO. 114 230A
JUNE 30, 2014
PREPARED FOR:
LARRY & LISA SINGER
2621 COUNTY ROAD 100
CARBONDALE, COLORADO 81623
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
- 1 -
PROPOSED CONSTRUCTION
-1-
SITE CONDITIONS
-2-
FIELD EXPLORATION
-2-
SUBSURFACE CONDITIONS
3 -
FOUNDATION BEARING CONDITIONS
- 3 -
DESIGN RECOMMENDATIONS
FOUNDATIONS - 4 -
FLOOR SLABS - 4 -
UNDERDRAIN SYSTEM - 5 -
SURFACE DRAINAGE - 5 -
- 6 -
LIMITATIONS
6 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 5 - GRADATION TEST RESULTS
TABLE 1- SUMMARy OF LABORATORY TEST RESULTS
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for proposed additions to the current
residence and a new RV Storage/Greenhouse Structure located at 2621 County Road 100,
east of Carbondale, 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 proposal for geotechnical engineering services to you
dated June 9, 2014.
A field exploration program consisting of exploratory borings 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 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 addition to the existing residence is an attached two story addition on the
east side of the residence and the RV Storage and Greenhouse Structure will be located
southwest of the existing residence. The attached addition to the house will have a slab -
on -grade or a structural floor over a crawlspace and be of similar construction to the
existing residence. Ground floors for the RV Storage and Greenhouse Structure will be
slab -on -grade. Grading for the additions is assumed to be relatively minor with cut
depths between about 2 to 4 feet. We assume relatively light foundation loadings,' typical
of the proposed type of construction.
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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.
SITE CONDITIONS
The site is currently occupied with a single family residence located in the middle of the
lot. The lot is bounded to the north by the Roaring Fork River, to the south by County
Road 100 and to the east and west by adjacent residential Lots. A small outbuilding is
located northeast of the residence and adjacent to the Roaring Fork River. The lot is
relatively flat with a slight slope down to the north. Shallow irrigation trenches cross the
southwest portion of the site. Vegetation on the Iot consists of grasses, shrubs and mature
trees.
FIELD EXPLORATION
The field exploration for the project was conducted on June 19, 2014. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface
conditions. The borings were advanced with 4 inch diameter continuous flight augers
powered by a truck -mounted CME -45B drill rig. The borings were logged by a
representative of Hepworth-Pawlak Geoteclmical, Inc.
Samples of the subsoils were taken with a 1% inch 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 of the
subsoils. Depths at which the samples were taken and the penetration resistance values
are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to
our laboratory for review by the project engineer and testing.
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-3 -
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils consist of about 4 to 6 inches of topsoil overlying silty sandy gravel with
cobbles and boulders. 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.
Laboratory testing performed on samples obtained from the borings included natural
moisture content and gradation analyses. Results of gradation analyses performed on
small diameter drive samples (minus 1 /z inch fraction) of the coarse granular subsoils are
shown on Figure 4. The laboratory testing is summarized in Table 1.
Free water was encountered in Boring I at 7 feet at the time of drilling and at 4'h feet
when checked 12 days later. Boring 2 caved at shallow depth during auger removal and a
water level check was not possible. The 5 foot sample from Boring 2 was wet. Subsoils
above the water table were slightly moist to moist.
FOUNDATION BEARING CONDITIONS
Foundations bearing on the natural granular soils encountered in our exploration should
be feasible for support of the proposed structure with some risk of movement. All
topsoil, any fill, and all loose or disturbed materials should be removed from the building
area and the foundation excavations extended down the natural relatively dense granular
soils. Groundwater was encountered in our exploration at relatively shallow depth and
may impact foundation construction and dewatering of' foundation or utility trench
excavations may be necessary.
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DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, we recommend the building additions and RV
Storage/Greenhouse Structure be founded with spread footings bearing on the natural
granular soils.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural granular soils should be
designed for an allowable bearing pressure of 2,500 psf. Based on
experience, we expect settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less.
2) The footings should have a minimum width of 16 inches for continuous
walls and 2 feet for isolated pads.
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 10
feet. Foundation walls acting as retaining structures should also be
designed to resist a lateral earth pressure.
5) Any existing fill, topsoil and any loose or disturbed soils should be
removed and the footing bearing level extended down to the relatively
dense natural granular soils. The exposed soils in footing area should then
be moistened if needed and compacted. If water seepage is encountered,
the footing areas should be dewatered before concrete placement.
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6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
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
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 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
Free water was encountered during our exploration and will likely fluctuate with river
levels, heavy precipitation and seasonal runoff. Frozen ground during spring runoff can
also create perched conditions. We recommend below -grade construction, such as
retaining walls and crawlspace areas, be protected from wetting and hydrostatic pressure
buildup by an underdrain system. If a crawlspace is constructed for the addition, shallow
seasonal groundwater may impact the crawlspace area and a sump with an adequate pump
may be necessary. Slab -on -grade construction should not require an underdrain system.
If 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% grade to a sump and pump. Free -draining granular
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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.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and
maintained at all times after the additions have 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 10 feet in unpaved
areas and a minimum slope of 3 inches in the first 10 feet in paved areas
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill and foundation areas.
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 borings drilled at the locations
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 fixture. If the client is
concerned about MOBC, then a professional in this special field of practice should be
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consulted. Our findings include interpolation and extrapolation of the subsurface
conditions identified at the exploratory borings 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
bearing strata and testing of structural fill by a representative of the geotechnical
engineer.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOC
James A. Parker, P.E., P.G.
Reviewed by:
P).4()0(4,L...
Daniel E. Hardin, P.E.
JAP/ ksw
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Job No. 114 230A
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LOCATION OF EXPLORATORY BORINGS
FIGURE 1
Elevation - Feet
6260
6255
6250
6245
BORING 1
ELEV.- 6254'
48/12
WC = 4.0
+4=51
-200=8
21/12
BORING 2
ELEV.— 6256'
40/12
29/12
WC=8.3
+4=55
-200=9
Note: Explanation of symbols is shown on Figure 3.
6260
6255
6250
6245
Efevation - Feet
114 230A
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LOGS OF EXPLORATORY BORINGS
FIGURE 2
LEGEND:
48/12
0, 12
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TOPSOIL; silty sand with gravel, roots, slightly moist, brown.
GRAVEL (GM); silty, sandy, with cobbles and boulders, medium dense to dense, moist to
wet, brown.
Drive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample, ASTM D-1586.
Drive sample blow count; indicates that 48 blows of a 140 pound hammer falling 30 inches were
required to drive the SPT sampler 12 inches.
Free water level in boring and days after drilling measurement was taken.
Depth at which boring had caved when measured after drilling.
Practical drilling refusal.
NOTES:
1. Exploratory borings were drilled on June 19, 2014 with 4 -inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided
and checked by instrument level.
4. The exploratory boring locations and elevations should be considered accurate only to the degree implied by the
method used.
5. The lines between materials shown on the exploratory boring logs represent the approximate boundaries between
material types and transitions may be gradual,
6. Water level readings shown on the logs were made at the time and under the conditions indicated. Fluctuations in
water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
114 230A
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LEGEND AND NOTES
FIGURE 3
RCENT RETAINE i�
HYDROMETER ANALYSIS I SIEVE ANALYSIS
TIME READINGS U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS
45MIN.1 7401
IN.60MIN19MIN.4 MIN. 1 MIN. /11200 #100 #50 7/30 1/16 #8 #4 3/8" 3/4' 1 1/2" 3" 5i'6" 8"
0
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20
30
40
50
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70
80
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100
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CLAY TO SILT
.019 .037 .074 .150 300 600 118 2.36
DIAMETER OF PARTICLES IN MILLIMETERS
FINE
GRAVEL 51
LIQUID LIMIT %
SAMPLE OF: Slightly Silty Sandy Gravel
SAND
4.75
9.5 12.5 190
GRAVEL
375
0
76.2 152 203
127
COBBLES
SAND 41 % SILT AND CLAY 8 %
PLASTICITY INDEX %
FROM: Boring 1 at 2 Feet
ME0894 ICOARSE
FINE I COARSE
HYDROMETER ANALYSIS I SIEVE ANALYSIS I
24 -IR. 7 HR TIME READINGS U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS
45 NIH. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 416 #8 #4 3/8" 3/4" 1 1/2" 3" 5'6' 8"
100
10
20
30
40
50
60
70
80
90
100
0
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.512 519.0 37.5 76.2 721752 203
DIAMETER OF PARTICLES IN MILLIMETERS
90
80
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70
60 4
50
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0_
30
20
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CLAY TO SILT
GRAVEL 55 %
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sandy Gravel
SANG
FINE I MEDIUM I COARSE
GRAVEL
FINE 1 COARSE
COBBLES
SAND 36 % SILT AND CLAY 9 %
PLASTICITY INDEX %
FROM Boring 2 at 2 and 5 Feet Combined
GeStech GRADATION TEST RESULTS
114 230A
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Job No. 114 230A
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