HomeMy WebLinkAboutSoils Report 10.02.2017H-PKUMAR
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 ACCESSARY DWELLING UNIT
811 EAST DIVIDE CREEK ROAD
SPRING CREEK RANCH
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-693
OCTOBER 2, 2017
PREPARED FOR:
STANGLE & SON BUILDERS, INC.
ATTN: GEOFF STANGL
P.O. BOX 3680
BASALT, COLORADO 81621
ge off Ccl stangibuilders.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 and 5 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 6 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
H-P%KUMAR
Proiect No. 17-7-A93
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed ADU to be located on the Spring
Creek Ranch, 811 East Divide Creek Road, 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 Stangl & Son Builders dated September 13, 2017.
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, 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 accessory dwelling unit will be a 1 and 2 -story structure located in the eastern part
of the ranch facilities as shown on Figure 1. Ground floor will be structural above crawlspace or
slab -on -grade. Grading for the structure 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.
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-P--t-KIJMAR
Prniart Nn 17.7-RQ1
-2 -
SITE CONDITIONS
The building site was vacant and located in a fenced field at the end of the ranch gravel road.
The ground surface was relatively flat with a gentle slope down to the west with about 5 feet of
elevation difference across the building footprint. A broad, dry drainage swale crosses the north
side of the building site which we understand will be diverted or blocked in the field uphill to the
east. Vegetation consists of sparse grass and weeds and scattered brush. Boulders were exposed
on the ground surface of the building area some of which may have been piled together.
FIELD EXPLORATION
The field exploration for the project was conducted on September 20, 2017. Three 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 and were logged by a representative of H-P/Kumar.
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 Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about one foot of topsoil overlying medium dense/very stiff, stratified clayey
sand and sandy clay down to depths of 4 to 111/ feet where dense, silty clayey sandy gravel with
cobbles and probably boulders were encountered. Drilling in the dense, coarse granular soils
with auger equipment was difficult due to the cobbles and boulders and drilling refusal was
encountered in the gravel deposit.
H-P*KUMAR
Prninnt No 17 -7 -RAR
3
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell -consolidation testing performed on
relatively undisturbed drive samples, presented on Figures 4 and 5, indicate low to moderate
compressibility under conditions of loading and wetting. The sample from Boring 2 at 21/ feet
showed a low collapse potential (settlement under constant load) when wetted. Results of
gradation analyses performed on a small diameter drive sample (minus 11 inch fraction) of the
coarse granular subsoils are shown on Figure 6. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The natural soils encountered at typical shallow footing depth are suitable for support of the
building foundation. The sand and clay soils have variable bearing and settlement/heave
potential mainly if the bearing soils are wetted and precautions should be taken to keep the
bearing soils dry.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,500 psf. Based on experience, we expect
H-Pk-KUMAR
Proiect Nn. 17-7-R93
-4 -
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. There could be additional foundation movement of about
1/z inch if the bearing soils are wetted.
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 12 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 topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural soils. The exposed soils in
footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate 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 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. Backfill should not contain organics
or rock larger than 6 inches.
H-P*KUMAR
Project No. 17-7-R93
-5 -
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 near optimum moisture content. 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 350 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.
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
H-P%KUMAR
Proiect No. 17-7-693
-6 -
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 free -
draining gravel should underlie below grade (basement level) 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 2% 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
Although free water was not encountered during our exploration, it has been our experience in
the area and where there are clay soils 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,
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
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.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
H-PKUMAR
Prnipri Nn 17.7-RQ'4
-7-
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. Free -draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site clayey soils
to reduce surface water infiltration.
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 the time of this study. 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 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 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.
H-P%KUMAR
Proiect No. 17-7-693
-8
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,
H -P; KUMAR
Steven L. Pawlak, P.E.
Reviewed by:
Daniel E. Hardin, P.E.
SLP/KAC
H-P%KUMAR
Project No. 17-7-693
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17-7-693
H -P- KUMAR
LOCATION OF EXPLORATORY BORINGS
Fig. 1
w
w
la.
ti
w
100
— 95
90
BORING 1
EL. 100'
r
r
.e.7
fa
14/12
WC=14.4
DD=112
15/12
WC=1 1.4
D0=118
BORING 2
EL. 96'
16/12
WC=3.6
DD=100
71/12
WC=4.4
DD=123
+4=49
—200=21
BORING 3
EL. 98'
15/12
WC=11.0
D0=116
—200=77
18/12
24/6,50/3
100 --
95 --
90
85 85
80 80
17-7-693
H-P--15KUMAR
LOGS OF EXPLORATORY BORINGS
1-
w
w
i
x
1-
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w
Fig. 2
LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN.
N1
y r SAND AND CLAY (SC—CL); SILTY, MEDIUM DENSE/VERY STIFF, SLIGHTLY MOIST, BROWN,
SLIGHTLY POROUS AND CALCAREOUS, LOW PLASTICITY, STRATIFIED.
GRAVEL (GM—GC); SILTY, CLAYEY, SANDY, COBBLES, POSSIBLE BOULDERS, DENSE, SLIGHTLY
MOIST, MIXED BROWN.
RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON
SAMPLE, ASTM D-1586.
11/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 11 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
t PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 20, 2017 WITH A 4—INCH DIAMETER
CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS ELEVATION 100', ASSUMED.
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 THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
17-7-693
H-P4
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
1
0
—1
—2
—3
—4
17-7-693
1 0 APPLIED PRESSURE - KSF
H -P- KUMAR
10
SWELL—CONSOLIDATION TEST RESULTS
100
Fig. 4
SAMPLE OF: Very Sandy Silty Clay
FROM: Boring 1 0 5'
WC = 14.4 %, DD = 112 pcf
--,--
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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17-7-693
1 0 APPLIED PRESSURE - KSF
H -P- KUMAR
10
SWELL—CONSOLIDATION TEST RESULTS
100
Fig. 4
1
RK
It
CONSOLIDATION - SWELL
2
0
—2
—4
—6
—8
—10
—12
17-7-693
1.0 APPLIED PRESSURE — 1[Sf
H -P KUMAR
10
SWELL—CONSOLIDATION TEST RESULTS
100
Fig. 5
SAMPLE OF: Silty Clayey Sand
FROM: Boring 2 ® 2.5'
WC = 3.6 %, DD = 100 pcf
'�.-r
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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— --
17-7-693
1.0 APPLIED PRESSURE — 1[Sf
H -P KUMAR
10
SWELL—CONSOLIDATION TEST RESULTS
100
Fig. 5
HYDROMETER ANALYSIS
SIEVE ANALYSIS
24 HRS 7 HRS
175 YIN- 15 MN IOW
TIME READINGS
tpolJ[f
4A1N
.1MIN 1
U.S.
OD 1/1211.
STANDARD
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CLEM 39114/rE OPENINGS
W4 1 2 4- 50
100
rag
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,
90
i
1
r
10
50
1
I
20
1
1
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70
1
30
1
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90
1
4
2
40
f
1
w
1
f
1
70
I
40
1
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1
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1
1
70
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20
1
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90
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1
10
L
90
rt
L
r
0 L 1 I1 Ei---A
.901 .001 .905 .002 .019
M
.007
.077
DIAMETER
.150 .300 1 .100 t.
OF PARTICLES IN MILLIMETERS
5 1 2.39
II
4.74 9
9 19
35.2
79.;
127
102
100
000
J
CLAY TO SILT
SAND
GRAVEL
FINE I MEDIUM COARSE
FINE I COARSE
COBBLES
GRAVEL 49 X SAND 30 X SILT AND CLAY 21 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Silty Clayey Sandy Gravel FROM: Boring 2 0 5'
Thns 15sl results oppTy only to th■
.umplet which wore tooled. The
looilnpp report shelf net .b. reproduced,
except In full, withaul lhr written
opproroi of Numor h Atioclplea. Inc.
51ovr =strolls feeling Is performed In
accordance wqh ASTM 0422, ASIA C135
and/0r *1114 01140.
17-7-693
H -P- KUMAR
GRADATION TEST RESULTS
Fig. 6
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-693
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pe)
GRADATION
PASPERCENT
NO 5200 ING
SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(13 SF)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(%)
SAND
(o )
LLI�MI T
(%)
PINDEXC
(%)
1
5
14.4
112
Very Sandy Silty Clay
10
11.4
118
Very Silty Clayey Sand
2
21/2
3.6
100
Silty Clayey Sand
5
4.4
123
49
30
21
Silty Clayey Sandy Gravel
3
21/2
11.0
116
77
Sandy Silty Clay