HomeMy WebLinkAboutFile Documents.210 S 1st St.0281.2017 (14).ARBK -1 ti KU MAR 5020 County Road 154
Glenwood Springs,CO 81601
Geotechnical Engineering I Engineering Geology Phone: (970)945-7988
Materials Testing I Environmental Fax: (970)945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker,Glenwood Springs,and Silverthorne, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED FIRST STREET HOUSE
210 S. FIRST STREET
ASPEN, COLORADO
PROJECT NO. 17-7-382
MAY 26, 2017
PREPARED FOR:
GRETCHEN GREENWOOD ARCHITECT, INC.
ATTN: GRETCHEN GREENWOOD
210 SOUTH GALENA STREET,SUITE 30
ASPEN, COLORADO 81611
(greenwood@ggaaspen.com)
RECEIVED
10/09/18
ASPEN
BUILDING DEPARTMENT
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS -2 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS -4 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 5 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 6 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 —GRADATION TEST RESULTS
TABLE I—SUMMARY OF PERCOLATION TEST RESULTS
RECEIVED
10/09/18
H-PKUMAR
Project No. 1 -7�gg A� SPEN
Uit.UIIVG DEPARTMENT
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at 210 S.
First Street, Aspen, 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 Gretchen Greenwood
Architect, Inc. dated May 10, 2017.
An exploratory boring was drilled 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 two story wood frame construction above a basement. The upper
floor will extend above a concrete driveway on the east side. Ground floor will be slab-on-grade.
Grading for the structure is assumed to be relatively minor with cut depths up about 10 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.
SITE CONDITIONS
The property is occupied with an existing residence on the north side. The existing house is one
story above a basement. There is a lawn area and gravel driveway on the southern portion of the
property. The ground surface is relatively flat with a slight slope down to the northwest. An
existing drywell is located at the southwest corner of the existing house. An existing building
above a basement is located about 5 feet from the property line on the east side. RECEIVED
10/09/18
H-PkKUMAR
Project No. 17-7-382ASPEN
BUILDING DEPARTMENT
- 2 -
FIELD EXPLORATION
The field exploration for the project was conducted on May 17, 2017. One exploratory boring
was drilled at the location shown on Figure I to evaluate the subsurface conditions. The boring
was advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-
45B drill rig. The boring was logged by a representative of H-P/Kumar.
Samples of the subsoils were taken with a 1% inch I.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
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 3 feet of man-placed fill overlying silty sandy gravel with cobbles and
small boulders. Drilling in the dense granular soils with auger equipment was difficult due to the
cobbles and boulders.
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' inch fraction) of the coarse granular subsoils are shown on Figure 3.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The natural granular soils are adequate for support of spread footing foundations. Man-placed
fill adjacent to the existing basement and from previous site grading should be removed from
beneath proposed foundations. The City of Aspen requires an engineered excavation
stabilization plan if proposed foundations are within I5 feet of a neighboring structure or RECEIVED
10/09/18
H-PEKUMAR
Project No. 17-7-382ASPEN
BUILDING DEPARTMENT
- 3 -
travel way. The plan is not required if excavations are less than 5 feet below existing grades or
further than 15 feet from travel ways and less than 15 feet deep. Slope bracing through use of a
variety of systems such as chemical grouting, micro piles and soil nails should be feasible at the
site. A shoring contractor should provide design drawings to support the proposed excavation
slopes. Other City requirements may also be applicable.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building 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.
I) 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 l6 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 42 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
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) All 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 and co1nr t CEIVED
10/09/18
H-Pt-KUMAR
Project No. 17-7-3824SPEN
!BUILDING DEPARTMENT
-4 -
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 45 pcf for backfill consisting
of the on-site granular 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 Ieast 40 pcf for backfill consisting of the on-site granular 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 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 400 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate slIErEIvED
10/09/18
H-PtKUMAR
Project No. 1 - ASPEN
biUTLUING DEPARTMENT
- 5 -
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
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 be placed beneath 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 granular 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 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 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 sump and pump or drywell. Free-draining granular material used in the underdrain system
RECEIVED
10/09/18
H-P t KUMAR
Project No. 17-7-3826\SPEN
BUILDING DEPARTMENT
- 6 -
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 backfiIl 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:
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 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
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.
DRYWELL
We understand the existing drywell will be used for site runoff detention and disposal. The
Natural Resources Conservation Service has identified four hydrologic soil groups (HSG) in the
Aspen area and the site is located in Type B soil having a moderate infiltration rate. Results of a
percolation test performed 10 feet south of Boring 1 are shown on Table I. The groundwater
level and bedrock are generally known to be relatively deep in this area.
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 1, the proposed type of CEIVERE
10/09/18
H-P z KUMAR
Project No. 17-7-382ASPEN
BUILDING DEPARTMENT
- 7 -
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 bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
2 U MAP
Louis E. Eller
Reviewed by:
fr-
•Davie E. Hardin, P. �, 9)•,r2
.Q 24443 z
LEE/kac '. 1
RECEIVED
10/09/18
H-PtKt1MAR
Project No. 17-7-382ASPEN
BUILDING DEPARTMENT
HOPKINS AVENUE
-7896-e_
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APPROXIMATE SCALE-FEET
17-7-382 H-PtiKI IMAR LOCATION OF EXPLORATORY BORING Fig "1 9 118
ASPEN
BUILDING DEPARTMENT
BORING 1 LEGEND
EL. 7898.5'
0 FILL; SANDY CLAY AND GRAVEL, COBBLES, MEDIUM DENSE, MOIST, DARK
BROWN. OVERLAID BY 6 INCHES OF TOPSOIL.
38/12 GRAVEL (GM); WITH COBBLES AND BOULDERS, SANDY, SILTY, DENSE,
WC-1.9 ' o SLIGHTLY MOIST, BROWN.
+4=60
5 -200=6 DRIVE SAMPLE, 1 3/8-INCH I.O. SPLIT SPOON STANDARD PENETRATION 35/12
TEST.
38/12DRIVE SAMPLE BLOW COUNT. INDICATES THAT 38 BLOWS OF A
140-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE
THE SAMPLER 12 INCHES.
w
10
50/5
— NOTES
WC=2.1 1. THE EXPLORATORY BORING WAS DRILLED ON MAY 17, 2017 WITH A
+4=39-200=9 4-INCH DIAMETER CONTINUOUS FUGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
15 APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN
— , .1 60/12 PROVIDED.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED BY
INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE
20 CONSIDERED ACCURATE ONLY 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 THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF
DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
CEIVED
17-7-382 H-P- MAR LOG OF EXPLORATORY BORING Fi%/'209 /18
ASPEN
BUILDING DEPARTMENT
HYDROMETER ANALYSIS SIEVE ANALYSIS
Tlsl[O[ADINOS U S,"3TANDARO SERIES - CLCAR SQUARE OPENINGS
241119 71113 I
100 I NIN,fa rat lDJIM E1yIN prat I!$L • 1 . 10 4p C O AJ A( S 3 "..
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.001 .Rea .003 001 0 .037 S .ISO J00 I .100 1.1/ I2.31 4.75 U.S Is 3/.1 1.2 1271:00
L_ DIAMETER OF PARTICLES IN MILLIMETERS _ 152
_I
CLAY TO SILT SAND GRAVEL COBBLES
FINE I MEDIUM COARSE, FINE 1 COARSE
GRAVEL 60 X SAND 34 X SILT AND CLAY 6 %
LIQUID UMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sandy Gravel FROM: Baring 1 O 2.5 & 5'
HYDROMETER ANALYSIS SIEVE ANALYSIS
TAlE READINGS Y.S.STANOA.O SERIES I CLLAA SQUARE 07E1111103
24 IIRS 7 113
100 AS InN JS MIN 0U111 11MIN AWN !IRN 1390 /l00 140JA 1 a /10 f0 t4 3/- 3 4� 1 t a r
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.001 .002 .00/ .0011 .01, .037 .075 .130 .300 I .100 1.1/ I3.3a 4.73 U.S 11 31.1 702 137 300
DIAMETER O_PARTICLES IN MILLIMETERS 157
F
SAND T GRAVEL T
COBBLES
CLAY TO SILT - - - `
FINE i MEDIUM COARSE FINE J COARSE
K
E GRAVEL 39 X SAND 52 X SILT AND CLAY 9 %
UQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sand and Gravel FROM: Baring 1 O 10 8 15'
This. test results apply eniy to the
L samples which win listed. The
f fisting report shall not be npreduc.d.
except In lull, wilhout the written
approval of Kumer A Associate,. Inc.
SlaveL telling Is old
occordOnc. with ASTM D
-� and/orr AST ASTM 01140. -a
17-7-382 H-P-~KUMAR GRADATION TEST RESULTS fiq.p 'o9/18
ASPEN
BUILDING DEPARTMENT
H-P1<UMAR
TABLE I
PERCOLATION TEST RESULTS
PROJECT NO. 17-7-382
F - -
HOLE NO. HOLE LENGTH OF WATER WATER DROP IN AVERAGE
DEPTH INTERVAL DEPTH AT DEPTH AT WATER PERCOLATION
(INCHES) (MIN) START OF END OF LEVEL RATE
INTERVAL INTERVAL (INCHES) (MIN./INCH)
(INCHES) (INCHES)
1 fi 12-4 2 28 231/4 4% .4
I '
231 201/4 3 .7
201/4 171/4 3 ,7
171/4 14 31/4 .6
14 11 3 .7
_
11 7 4 .5
Note: Percolation test was performed in a 10 foot deep boring located about 10 feet
south of Boring 1.
RECEIVED
10/09/18
ASPEN
BUILDING DEPARTMENT