HomeMy WebLinkAboutFile Documents.108 Midland Ave.0264.2017 (21).ARBK H-P 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 Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED SANDLER RESIDENCE
108 MIDLAND AVENUE
ASPEN, COLORADO
PROJECT NO. 17-7-160
MARCH 8, 2017
PREPARED FOR:
108 MIDLAND AVENUE ASPEN, LLC
C/O POSS ARCHITECTURE+PLANNING
ATTN: PHILIPPE-ANTOINE BEAUREGARD
605 EAST MAIN STREET •
ASPEN, COLORADO 81611
(pbeauregard @ billposs.com)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
MINE SUBSIDENCE - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 6 -
UNDERDRAIN SYSTEM - 7 -
DRYWELL - 7 -
SURFACE DRAINAGE - 8 -
LIMITATIONS - g -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
TABLE 1 -SUMMARY OF LABORATORY TEST RESULTS
TABLE 2-PERCOLATION TEST RESULTS
RECEIVED
10/16/2017
H-P*.KUMAR Project No. 17-7-160
ASPEN
BUILDING DEPARTMENT
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for the proposed Sandler residence to be
located at 108 Midland Avenue, 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 108 Midland
Avenue Aspen, LLC, dated January 18, 2017.
A field exploration program consisting of an exploratory boring 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 construction consists of removing the existing residence shown on Figure 1 and
building the new residence in its place. The new residence will be 2 and 3-story wood frame
construction above a walkout basement level on the west side. Ground floors will typically be
slab-on-grade with some structural floors above crawlspace. Grading for the structure will
involve cut depths up to about 15 feet. Excavation shoring may be needed to maintain cut slope
stability. We assume relatively light to moderate foundation loadings, typical of the proposed
type of construction. The existing pond on the east side will be removed and replaced with a
stream east of the property line.
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.
RECEIVED
Project No. 17-714d 16/2 017
H-P�KUMAR
ASPEN
BUILDING DEPARTMENT
- 2 -
SITE CONDITIONS
The property is occupied by an existing 2-story residence with a walkout basement level. The
west part of the property is a steep slope down to Midland Avenue from the house and concrete
driveway slab and parking area. The ground surface within the building area is relatively flat
and gently sloping down to the southwest. A small pond is located immediately east of the
building. Vegetation consists of scattered evergreen trees and landscaping. About 1 to 2 feet of
snow covered the property at the time of our field exploration.
MINE SUBSIDENCE
Mine workings underlie portions of the Aspen area. The workings are primarily underground
tunnels between Aspen and Smuggler Mountains southeast and east of the downtown area. The
workings consist of numerous tunnels beginning a few hundred feet below the ground surface
becoming shallower to the south. Under certain conditions these workings can collapse and
cause surface subsidence. The subject site appears to be located outside of and about 800 feet
east of these main tunnel workings.
Our exploratory boring was drilled relatively shallow and for foundation design only, however,
no indications of subsurface voids were found at the subject site. We believe the risk of
subsidence due to the collapse of underground mine works throughout the service life of the
proposed residence to be low. If further evaluation of the mine works subsidence potential at the
site is desired, we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on February 20, 2017. One exploratory
boring was drilled at the approximate location shown on Figure 1 to evaluate the subsurface
conditions. Drill rig access to other parts of the property was not practical due to site features
and snow cover. The boring was advanced with 4-inch diameter continuous flight augers RECEIVED
10/16/2017
H-P-KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
- 3 -
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 2-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
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils, below the concrete slab and about 15 feet of silty clayey sand and gravel fill consist of
natural, relatively dense, silty sandy gravel and cobbles with probable boulders to the boring
depth of 161/feet. Drilling in the coarse granular natural soils was difficult due to the cobbles
and probable boulders and practical auger refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density, and finer than sand size gradation analyses. The laboratory test results are
summarized in Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist to moist.
FOUNDATION BEARING CONDITIONS
The natural granular soils encountered below the fill materials are adequate for support of spread
footing foundations. The man-placed fill should be completely removed from beneath the
proposed building area. We understand that the foundation of the existing residence on the north
and west sides was underpinned with helical piers in 1999 due to settlement and distress. It
appears the north and west parts of the existing residence overlie considerable fill depth which could be the cause of building settlement. The new building as planned is above a full basREC E IVE D
10/16/2017
H-Pk-KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
-4 -
and the excavation may extend down below the fill material in the uphill, eastern part but will
apparently overlie existing fill in the western part. Further evaluation of the extent of existing
fill will be needed at the time of excavation.
The City of Aspen requires an engineered excavation stabilization plan if proposed foundations
are within 15 feet of a neighboring structure or public 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 micro-piles
and soil nailing should be feasible at the site. A shoring contractor with experience in the area
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 or properly placed and compacted structural fill.
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 or compacted structural
fill should be designed for an allowable bearing pressure of 3,000 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 42 inches below exterior grade is typically used in this
area.
RECEIVED
10/16/2017
H-P--KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
- 5 -
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 existing fill soils, debris 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
compacted. Structural fill placed to re-establish design bearing level should
consist of a relatively well graded granular soil compacted to at least 100% of
standard Proctor density at near optimum moisture content. The fill should
extend laterally out from the footing edges a distance at least equal to the depth of
fill below the footing. As a foundation settlement consideration, the fill depth
below the footing bearing level should not exceed about 6 feet.
6) A representative of the geotechnical engineer should observe all footing
excavations and test structural fill placement compaction 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 granular soils or imported granular materials. Cantilevered retaining structures
which are separate from the building 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
granular soils or imported granular materials. The backfill should not contain debris, topsoil or
oversized (plus about 6 inch) rock.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipmenk E'VED
10/16/2017
H-P�KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
- 6 -
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 over compact 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. Increasing compaction to at least 98% of standard Proctor
density could be used to help limit the settlement potential.
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 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 relatively well graded granular soil
compacted to at least 95% of the maximum standard Proctor density at a moisture content near
optimum.
FLOOR SLABS
The natural granular soils encountered below the existing fill 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 bRE(EIVED
10/16/2017
H-P-KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
- 7 -
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 debris, topsoil and rock larger than about 6 inches.
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, 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, drywell or sump and pump. 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 feet deep.
DRYWELL
Drywells and bio-swales are often used in the Aspen area for site water runoff detention and
disposal. The natural granular soils encountered below the fill soils are typically relatively free
draining and should be suitable for surface water treatment and disposal as needed. The results
of percolation testing performed in Boring 1, presented in Table 2, indicate an infiltration rate
between about 1/a and 1/2 minutes per inch for the soils below basement level. Bedrock and
groundwater level are generally expected to be relatively deep compared to the proposed lower �� CC`�/
floor level and not affect drywell or bio-swale design. If a drywell is used, it should have RECEIVED
ED
10/16/2017
H-Pk-KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
- 8 -
casing down to at least 2 feet below basement floor level with perforations below that level. The
proposed stream to the east of the property line must be lined with an impervious membrane to
not affect groundwater flow conditions at the building site.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the building 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 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. Free-draining wall backfill should be
covered with filter fabric and capped with at least 2 feet of 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 5
feet from foundation walls.
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 boring drilled at the location 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 professiR ltC E IVE LEA
10/16/2017
H-P�KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
- 9 -
this special field of practice should be consulted. Our findings include 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,
H-P-KUMAR
r
° .0} d4
411.r, Y
Steven L. Pawlak, P.E. , ° I
I 3/91il D.
Reviewed by: 1(8�
sK k Q. ir^
+`44...a... �,r
" OFCOS.-
,.,..,,1/4.T?
David A. Young, P.E.
SLP/ksw
RECEIVED
10/16/2017
H-Pk-KUMAR Project No. 17-7-160ASPEN
BUILDING DEPARTMENT
rj ., IMPR
tIy,q- L
dfam* "+ �,�`*.
r• F..' fr,,.-, - _ ^tip r�
rr ` .•
// •`� 1 aft'/ t ' r t
y
` SLIM
p
IJ + Yam... I� t�� -t{ 't.I 1
i ' . tr w• 1 I r..ry'tiE
i I • tad #,: t,• •( J PI•I ,,i 4 Y—
i. .iI 'E 6r`i',
f, 1 at ,zr
It - I t r 4 • 1�';i• I _1...r, ^ ^ •1.•• a,,Maz i.
t + BORING 1 .r,, �I 1 _r ,�Ey_y%�
Pa_ / r. ' r._-: --
.1 /
tIt . / t 'I i a •./rl�e
ii,
j• J •1 i /7777 �J� r
/. .r' • ff �-
f
g
; � / g .7. •e t x • +� hpl.Ad#• fr y
7/ f r , , y .
/ , t -_ s ! y' J
. , ", .,. ' 1,.1';• A );4'. •/ .fir
/' t ��r t g• 7. t• :may,� ,=,ti{ 'eS
i J tt _ J _y,�4 i : * _ 1
II .i /�' .• `. •• a •r i'�ay f1 we
rt t i s \ ♦•. -y•!•'•✓' " - ftt N / {` rill
• '/
fo.
S ''1/ J fr_ ✓
f L' r r
t t !J
/ / i t
,S5 _o
No so twism
15 0 15 30
APPROXIMATE SCALE—FEET
RE :ENVED
17-7-160 H-PtiKUMAR LOCATION OF EXPLORATORY BORING F,ilg. 11F%,2017
ASPEN
BUILDING DEPARTMENT
LEGEND
BORING 1
EL. 7973' (4) CONCRETE PAVEMENT, THICKNESS IN INCHES SHOWN IN
PARENTHESES TO LEFT OF THE LOG.
7975 —
FILL; SILTY SANDY GRAVEL, MEDIUM DENSE, MOIST, BROWN.
(4) itiown
♦ 1��
�� FILL; SILTY CLAYEY SAND AND GRAVEL, MEDIUM DENSE,
30/12 � 4 SLIGHTLY MOIST TO MOIST, DARK BROWN,
►��� WC=4.8
7970 o DD=111
I 1 GRAVEL AND COBBLES (GM); SILTY, SANDY, DENSE, SLIGHTLY
���' WC-152.7 i MOIST, MIXED BROWN. ROUNDED ROCK.
DD=91
u_ 1 4 —200=27 DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
— ► 4 _
0 7965 o
16/12 30/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 30 BLOWS OF
> ►�� WC=7.4 A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED
w— o � DD=110 TO DRIVE THE SAMPLER 12 INCHES.
IIf
n -200=22PRACTICAL AUGER REFUSAL.
7960 BASEMENT FLOOR NOTES
ELEV=7962'
1. THE EXPLORATORY BORING WAS DRILLED ON FEBRUARY 20, 2017
50/3 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE
PLAN PROVIDED.
7955
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
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);
•
DD = DRY DENSITY (pcf) (ASTM D 2216);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
I
A
AT
nE RcEVED
17-7-160 H-PKUMAR LOG OF EXPLORATORY BORING
10/16/2017
ASPEN
BUILDING DEPARTMENT
o
o
w w u;
75
ti > > >
w 0 cG cd
z C7 C7 C7
'~ J_
0 'L3
a) 0 Cv C`i c-J
O c c al
EL ciD
, ›,
pw
w?2
LL�o
0_ a
HZ00co
J U
D
co 0
W H 1-w
a.
// w —
£r 0 a -'
,i H
L-i s- Q
=7--..-_1 J 0 w w z z o
l l �Q J —Q uj
CC z� N N
aa N
LL
' O p
ocl 111111 II
O co
2 a.
Cn 0 :;oIIIIIIIIIIIII
J w H
<ccz
f-COz -7- tri N
Qoo
Z a 0
Z 2
O 1 N O
Q p
U
01
o R ; CEIVED
• z
cn
• m 1o /16/2017
ASPEN
BUILDING DEPARTMENT
H-P� I<UMAR
TABLE 2
PERCOLATION TEST RESULTS
PROJECT NO. 17-7-160
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)
B-1 184 2 241/2 171/2 7 0.3
171/2 8 91/2 0.2
8 2 6 0.3
Water Added 46 40 6 0.3
40 36 4 0.5
36 29% 61/2 0.3
291/2 231/2 6 0.3
Note: The percolation test was conducted in the completed 4-inch diameter borehole
on February 20, 2017.
RECEIVED
10/16/2017
ASPEN
BUILDING DEPARTMENT