HomeMy WebLinkAboutSoils Report 12.14.2018H -PKU MAR
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
RECr'" £ 'Z`
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 58, SPRING RIDGE RESERVE
HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
JOB NO. 18-7-699
DECEMBER 14, 2018
PREPARED FOR:
TREVOR RUONAVAARA
160 SPRING RIDGE DRIVE
GLENWOOD _SPRINGS, COLORADO 81601
(it:sileseor 55)
MAY i 2. 2019
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION » 1 -
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS .. - 2 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS . - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
58, Spring Ridge Reserve, Hidden Valley 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 general accordance with our proposal for
geotechnical engineering services to Trevor Ruonavaara dated November 3, 2018. Hepworth-
Pawlak Geotechnical previously performed a preliminary geotechnical study for the subdivision
and reported the findings in a report dated February 26, 2001, Job No. 101 126 and updated the
study in a report dated June 22, 2004.
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 residence will generally be a two-story wood frame structure with an attached
garage and slab -on -grade floors located within the lower part of the building envelope as shown
on Figure 1. Grading for the structure is assumed to be relatively minor with cut depths between
about 3 to 8 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.
-2 -
SITE CONDITIONS
The property was vacant at the time of our field exploration. The site is vegetated with grass,
weeds and sage brush with juniper and pinon trees to the east above the building area. The
ground surface in the general building area slopes gently to moderately down to the northeast at
about 8 to 10%. The grade steepens slightly in the upper lot area to about 15%, see Figure 1.
Maroon Formation sandstone is exposed on the hillside to the east of the lot.
FIELD EXPLORATION
The field exploration for the project was conducted on November 26, 2018. 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 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 subsurface materials 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 and hardness of the bedrock. 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
subsurface profiles were variable and below about 1/2 foot of topsoil consist of sandy silty clay to
a depth of 12 feet in Boring 1 overlying claystone/siltstone bedrock and in Boring 2 to a depth of
about 4 feet overlying sandstone bedrock. The bedrock became very hard with depth and
practical drilling refusal was encountered in the formation at Boring 2.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell -consolidation
-3 -
testing performed on relatively undisturbed drive samples of the clay soils, presented on Figure
4, generally indicate low to moderate compressibility under light loading and a low collapse
potential (settlement under constant load) or minor expansion potential when wetted. 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.
FOUNDATION BEARING CONDITIONS
The top of bedrock slopes down to the west and will probably be encountered in the upper part of
the building excavation and transition to sandy silty clay in the remaining areas of the
excavation. The clay soils are of variable compressibility potential and could tend to settle
especially when they become wetted. The expansion potential can probably be ignored in the
design but should be further evaluated at the time of excavation. A shallow foundation placed on
the clay soils will have a risk of settlement if the soils become wetted and care should be taken in
the surface and subsurface drainage around the house to keep the bearing soils dry. It will be
critical to the long term performance of the structure that the recommendations for surface
grading and subsurface drainage contained in this report be followed. Presented below are
recommendations for shallow spread footings with a risk of settlement. A low settlement risk
foundation support can be achieved by extending the bearing down into the underlying bedrock
such as with drilled or excavated piers. If a deep foundation is desired, we should be contacted
for additional recommendations.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
natural soils below topsoil or on bedrock provided the owner accepts the risk of settlement and
potential building distress.
-4 -
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 initial
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less. Additional differential settlement could be on the order of
1/2 to 1 inch for a limited wetted depth of around 10 feet below the footings. The
settlement could be differential compared to areas where footings are placed on
formation rock.
2) The footings should have a minimum width of 20 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 14 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 55 pcf for backfill consisting
of the on-site soils. Cantilevered retaining structures which are separate from the residence and
-5 -
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 45 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 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 325 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, can be used to support lightly loaded slab -on -grade
construction. There could be differential settlement potential from wetting of the bearing soils
-6 -
similar to that described above for footings. 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 relatively well graded sand and gravel such as road base should
be placed beneath slabs for 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 (plus 6 inch) rock.
We recommend vapor retarders conform to at least the minimum requirements of ASTM E1745
Class C material. Certain floor types are more sensitive to water vapor transmission than others.
For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor
transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum
requirements of ASTM E1745 Class A material. The vapor retarder should be installed in
accordance with the manufacturers' recommendations and ASTM El 643.
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, be
protected from wetting and hydrostatic pressure buildup by an underdrain system.
Where 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 dram 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
-7 -
the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at
least 11/2 feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the
drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting
of the bearing soils unless the bearing material is bedrock or non -moisture sensitive soil.
SURFACE DRAINAGE
Proper surface grading and drainage will be critical to limiting subsurface wetting below the
building. 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. Free -draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site 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 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
-8 -
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
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 % KLJMAR
Steven L. Pawlak, P.E. •
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
2,50
a
e 07,4 go
0,0
10"
LOT 59
i
BORING 1
-;
Rurkliq
J
! ! 1 /
BORING 2
03 1
44.cJi
LOT 58
9
I
! 1 i 1 {
/ f•
2: O''Bw1di: )0 ne.
1 1 i r , /
; 1,
15 0 15 30
APPROXIMATE SCALE -FEET
1 (V`ATIf1Ml nr GYPI f1PATf1PY Pm:InI(_C flr, 1
LOT 57
R 1 1 P -7_F00
Il.irr,or R. Acenrinfcc
1
1
74
hE
A 1R -7-R00 I KA A D
Li
L -
0w-
-- 0
— 5
— 10
15
20
25
BORING 1
EL. 6489'
1 55/12
9/12
WC=4.3
00= 105
13/12
WC= 4.3
DD=111
28/6,50/6
50/1
BORING 2
EL. 6496'
17/12
WC=3.3
00= 108
-200=42
60/12
WC =1.0
0
5
10
15-
20
25
I (Inc (W PYPI (IPATnIZY 1:11IPIKIng 1 Pin
LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, BROWN.
CLAY (CL); SILTY, SANDY, SCATTERED ROCK FRAGMENTS, STIFF TO VERY STIFF, SLIGHTLY
/ MOIST, RED, LOW PLASTICITY.
WEATHERED CLAYSTONE; SILTY, SANDY, HARD, SLIGHTLY MOIST, RED.
1 SILTSTONE/CLAYSTONE BEDROCK; VERY HARD, SLIGHTLY MOIST, RED. MAROON FORMATION.
SANDSTONE BEDROCK; SILTY, VERY HARD, SLIGHTLY MOIST, LIGHT RED. MAROON FORMATION.
RELATIVELY UNDISTURBED DRIVE SAMPLE; 2 -INCH I.D. CALIFORNIA LINER SAMPLE.
111 DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON
SAMPLE, ASTM D-1586.
55/12 DRIVE SAMPLE DLOW COUNT. INDICATES THAT 55 BLOWS OF A 140 -POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
All PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON NOVEMBER 26, 2018 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 D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
1 R_7_E,QQ 1 1-1_1)--A-MI IRAAD
I FrFNIl AND N(1TFR I Fin
CONSOLIDATION - SWELL
1
1
-3
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 0 5'
WC = 4.3 %, DO = 105 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE KSI' i0 10a
tomo UV mann araY only to I?*
�. t. d. LN 1R�finp uperl
oprival
�ncd rrot b� nproducrA [pail in
}ub. +7Ihel1 the siircei.p ... ne. 5,411of
Kumar owl Ay ..
Carwlldn Ion nn nmmed In
eenitlac. With th Anil 0-4716.
SAMPLE OF: Sandy Clay
FROM: Boring 1 0 10'
WC = 4.3 %. DD = 111 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
10 APPLIED PRESSURE — KSF 10 100
45
Y1f. 1R-7 -gQ0 i 1—I_D3A-J111 IRA D ! CWFI I _rnikICni IIIATIC1N1 TFCT RFC! II TC 1 Fin n
KUMAP
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 18-7-699
SAMPLE LOCATION
NATURAL 1 NATURAL
MOISTURE DRY
CONTENT DENSITY
(%1 (pan
GRADATION
PERCENTUNCONFINED
PASSING
NO. 200
SIEVE
ATTERBERG LIMITS
COMPRESSIVE
STRENGTH
(psfl
SOIL TYPE
BORING DEPTH
(ft)
GRAVEL
%
( )
SAND
(%)
LIQUID
LIMIT
(%u}
PLASTIC
INDEX
(%)
1
5
4.3
105
111
Sandy Silty Clay
10
4.3
Sandy Clay
2
21/2
3.3
108
42
Very Sandy Silty Clay with
Gravel
5
1.0
Weathered Sandstone
r