HomeMy WebLinkAboutSoils Report 08.03.2020Kumar & +kssaciates, loc.
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 69, IRONBRIDGE
RIVER BEND WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-390
AUGUST 3, 2020
PREPARED FOR:
HAROLD (HAL) HARPER
2565 GREENSBOROUGH CIRCLE
HIGHLANDS RANCH, COLORADO 80129
(1l2 o. now(ii), gm a i l.com)
_4_
on the natural coarse granular subsoils or compacted structural fill after removal of the
compressible silt and clay soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural gravel soils (below silt and clay soils)
or at least 3 feet of compacted structural fill should be designed for an
bearing pressure of 2,500 psf. B
allowable
ased on experience, we expect initial settlement
of tootings designed and constructed as discussed in this section will be about
1 inch or less. There could be around '% to 1 inch of additional settlement if the
fine-grained bearing soils are wetted.
2) The footings should have a minimum width of 18 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 heavily 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, at least 3 feet of silt and clay soils and any loose disturbed soils
should be removed and the footing bearing level extended down to the
undisturbed natural soils. The exposed soils in footing area should then be
moistened and compacted. Design footing grade can be re-established with
compacted structural fill. Structural fill should consist of a relatively well graded
sand and gravel such as CDOT Class 6 road base compacted to at least 98% of
standard Proctor density at a moisture content near optimum. The structural fill
should extend laterally beyond the footing edges a distance equal to at least half
the depth of fill below the footing.
6) A representative of the geotechnical engineer should evaluate the fill placement
for compaction and observe all footing excavations prior to concrete placement to
evaluate bearing conditions.
Kumar & Associates, Inc. Project No. 20-7-390
-5
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 fine-grained 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 fine-grained soils.
Backfill should not contain organics, debris or rock larger than about 6 inches.
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 0.50. 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 a compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
Kumar & Associates, Inc. Project No. 20.7-390
6
FLOOR SLABS
The natural on -site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade
construction with a risk of settlement where underlain by the silt and clay soils. 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. A minimum 4-inch layer of sand and gravel should be placed beneath
slabs for structural support and 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 soils or imported road base 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 that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff Frozen ground during spring runoff can also create a perched condition. We
recommend below -grade construction, such as retaining walls and basement areas, be protected
from wetting and hydrostatic pressure buildup by an underdrain system. Shallow crawlspace and
slab -on -grade garage areas should not need to be protected with 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 or drywell based on the underlying coarse granular soils. 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 t/z feet deep.
SURFACE DRAINAGE
Positive surface grading and drainage will be critical to limiting wetting of the bearing soils and
building distress. The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
Kumar & Associates, Inc. Project No. 20.7-390
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 at least 2 feet of the on -site finer graded
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.
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 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.
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
Kumar & Associates, Inc. Project No. 20.7.390
-8-
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,
Kumar & Associates, Inc.
Steven L. Pawlak, Ix -
Reviewed by:
Daniel E. Hardin, P.E.
SLP/KAC
Kumar & Associates, Inc. Project No. 20-7-390
173S
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APPROXIMATE SCALE -FEET
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20-7-390
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
1
1
-
• - 5
1-'
wk
w•
I
_'
a.
0
i0
-- 15
20
20-7-390
BORING 1
EL. 5955'
7/12
WC=5.1
DD=94
-200=68
7/12
WC=10.7
DD=99
62/12
WC=1.4
+4=40
-200=10
50/4
Kumar & Associates
DORINO 2
EL. 5953.5'
12/12
WC=6.2
DD=94
16/12
WC=5.3
DD=100
-200=85
23/6, 50/4
50/5
BORING 3
EL. 5952'
13/12
1 WC=4.9
J DD=97
-200=88
12/12
WC=4.3
DD=97
42/6, 50/3
WC=1.0
+4=37
-200=17
LOGS OF EXPLORATORY BORINGS
0
5
10
15
20
Fig. 2
DEPTH -FEET
LEGEND
7
L
TOPSOIL; ORGANIC SANDY SILT AND CLAY, BROWN, POSSIBLE FILL/DISTURBED SOILS IN
PLACES.
SILT AND CLAY (ML—CL); SANDY, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST, LIGHT BROWN.
SAND, GRAVEL & COBBLES (GM —GP); SLIGHTLY SILTY TO SILTY, PROBABLE BOULDERS,
DENSE, SLIGHTLY MOIST, BROWN, ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
111 DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
7/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 7 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JULY 17, 2020 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 OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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 D2216);
DD = DRY DENSITY (pcf) (ASTM D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
20-7-390
Kumar & Associates
LEGEND AND NOTES
CONSOLIDATION - SWELL
These teal :mule of0 only to the
tompNi leafed Thn leol;ry 'apart
WO not be rrpraaecd. inapt In
tuff. without the opro.al of
Renner and Asaoalatee, Inc. Swell
Con/4140w, taling beam -mid in
woordone wlp' ASV p-4i14.
20-7-390
SAMPLE OF: Sandy Silt and Clay
FROM: Boring 1 ® 5'
WC = 10.7 %, DD = 99 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPL1EQ PRESSURE - KSF 10
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
100
Fig. 4
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
-4
•
SAMPLE OF: Sandy Silt and Clay
FROM: Boring 2 ® 2.5'
WC = 6.2 %, DD = 94 pcf
1.0 APPLIED PRESSURE — KSF
These !tot tewAh web onH fa Ins
•ample lasted- The tt.th6 !cowl
hall not hr repreducod, asap! M
Tad .,!!heal the •ellen approve! el
Kemp end gyacIetto, Inc. Some
Camolldation Inllne performed In
cnn idence with AI 0-4546.
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1(1 100
SAMPLE OF: Sandy Silt and Clay
FROM: Boring 3 ® 5'
WC = 4.3 %, DD = 97 pcf
L`.
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE — KSF
10 100
20-7-390
Kumar & Associates
SWELL -CONSOLIDATION TEST RESULTS
Fig. 5
100
90
e0
70
60
50
40
30
HYDROMETER ANALYSIS
TIME READINGS
SIEVE ANALYSIS
il.S $7A11a]IIfD f[AIER CLEAR 50DRE OPENINGS
,[4 IIv: i` 4945
17 >•1# 15 I411.1 60141N 117.141N 464111 14411 #209. 0.100 ___050 445 ¢30 _ #16 iF1n><SB
20 --
10
I4
0 I 1 ! I! 7 i l l 1 1I I II I I i_I LII _i _I _I ll1
.051 .002 .005 .009 .019 037 07•, .150 .000 .600 1.18 2 " L75 9.5
L ❑IAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
5" 6- Co
10
20
I_ i.
4 38.1
SAND GRAVEL
FINE MEDIUM 'COARSE FINE 1 COARSE COBBLES
GRAVEL 40 % SAND 50 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sand and Gravel
HYDROMETER ANALYSIS
TIME READINGS
IT. HR5 7 F4R5
100 145 GAIN 15 MIN_7QMIM 16M444 4M161
90
60
70
60
50
40
30
20
10
U.S. !WPM) SERIES
SILT AND CLAY 10 %
FROM: Boring 1 0 10'
SIEVE ANALYSIS
30
40 1
50
BO
70
BO
90
1 III_
76,2 127 3.00
152 1
CLEAR SOUAR£ OPE4INGS
1MIF1 iyi ilioo 050 #40 #50 06 110 fO #.4 3/8' 3/4" I I 2 5 6
Q I--- __ - ._I_ _I_ L I.1�L_ - .L J___I I_ I IA IL_ _ I I_ I I -U.1.11_... _ _I_. I LI_I III_
.001 .002 .005 . os .019 .037 .075 .150 300 .425 .600 1.18 , 2.36 4.75 9.5
2.0
DIAMETER OF PARTICLES IN MILLIMETERS
SAND f GRAVEL
20-7-390
CLAY TO SILT
O
10
20
30
40
50 k
e0
70
BO
BO
I-__L. _I I . - 100
38.1 76.2 127. 200
152
FINE I MEDIUM .r,n,a FINE ! COARSE
GRAVEL 37 X SAND 46 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Silly Sand and Gravel FROM: Boring 3 0 10'
Kumar & Associates
SILT AND CLAY 17 %
COBBLES
Moos leaf resulla apply only to the
samples which ware listed. The
}ealing roport shall nat 6s rsproduc4d.
e11ce t in full. wlthoul lhs written
approval of Kumar ✓k Asscrlatst. Mv.
51896 onnlysIs fading is p8rtarm5d In
accerdonas with ASTM D6913. ASV D7928.
ASTM CISB and/or A5114 D1140.
GRADATION TEST RESULTS
Fig. 6
e'
Gessiech& l
nicaI and VateriafsrtEn.gineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
ipcfj
GRADATION
PERCENT
PASSING
GE�NO.
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(Psi)
SOIL TYPE
BORING
i DEPTH
(ft)
GRAVEL
(,fin)
SAND
%�
LIQUID LIMIT
(%)
PLASTIC
INDEX
(Ye)
1
2'/2
5.1
94
68
+
Sandy Silt and Clay
5
10.7
99
Sandy Silt and Clay
10
1.4
40
50
10
Slightly Silty Sand and
Gravel
2
2%2
6.2
94
Sandy Silt and Clay
5
5.3
100
85
Sandy Silt and Clay
3
2%2
4.9
97
88
Sandy Silt and Clay
5
4.3
97
Sandy Silt and Clay
10
1.0
37
46
17
Silty Sand and Gravel
-