HomeMy WebLinkAboutSoils Report 03.29.2019I (--A Kumar Via, aIs
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 6, RANCH AT ROARING FORK
SURREY STREET
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-190
MARCH 29, 2019
PREPARED FOR:
SANTIAGO MUSSI TISCORNIA
1501 WALZ AVENUE
GLENWOOD SPRINGS, COLORADO 81601
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION .. - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
SLABS -ON -GRADE - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - b -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY PITS
FIGURE 2 - LOGS OF EXPLORATORY PITS
FIGURE 3 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19-7-190
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 6,
Ranch at Roaring Fork, Surrey Street, 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 proposal for geotechnical engineering services
to Forma Estudio dated March 19, 2019.
A field exploration program consisting of exploratory pits 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 residence will to be a two story structure with attached garage. Ground floors are
assumed to be structural over crawlspace for the house and slab -on -grade for the garage.
Grading for the structure is assumed to consist primarily of filling to depths of about 3 to 5 feet.
We assume relatively light foundation loadings, typical of the proposed type of construction.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The natural ground surface is
gently sloping down to the west. The lot is low-lying relative to the adjacent street grade and
will be built up to accommodate the new construction. Elevation difference across the building
Kumar & Associates, Inc. Project No. 19-7-190
-2 -
area is about 5 feet and across the lot is about 8 feet. Vegetation consists of willow brush and
weeds. The willows were cleared from the area around the pits prior to the field exploration.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ranch at Roaring Fork
Subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsum and limestone. There is a possibility that massive
gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot.
Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can
produce areas of localized subsidence. During previous work in the area, several sinkholes were
observed scattered throughout the Carbondale area. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the Roaring Fork Valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory pits were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot 6 throughout the service life of the proposed residence, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
development. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on March 27, 2019. Two exploratory pits
were excavated at the locations shown on Figure 1 to evaluate the subsurface conditions. The
pits were dug with a mini excavator. The pits were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with relatively undisturbed and disturbed sampling methods.
Depths at which the samples were taken are shown on the Logs of Exploratory Pits, Figure 2.
The samples were returned to our laboratory for review by the project engineer and testing.
Kumar & Associates, Inc. Project No. 19-7-190
Footings placed on structural fill supported by the underlying natural granular
3
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of between '/2 and 1'/2 feet of topsoil overlying dense gravel and cobbles. Pit 1
encountered organic sand and silt from '/2 to 2 feet.
Laboratory testing performed on samples obtained from the pits included natural moisture
content and density and gradation analyses. Results of gradation analyses performed on a
sample of the gravel (minus 5 -inch fraction) are shown on Figure 3. The laboratory testing is
summarized in Table 1.
Free water was encountered in the pits at a depth of about 4'/2 feet at the time of exploration. The
subsoils were moist to wet with depth.
FOUNDATION BEARING CONDITIONS
We recommend the low-lying building area be raised to a level similar to the street grade using
structurally placed fill. The gravel and cobbles encountered in the pits possess moderate bearing
capacity and typically low compressibility potential. The upper topsoil and silt and sand layers
are unsuitable for foundation bearing and should be excavated before structural fill can be placed
to establish the foundation subgrade.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory pits and the nature of the
proposed construction, we recommend the building be founded with spread footings bearing on
granular structural fill placed on the natural granular soils. The existing topsoil and silt/sand
soils should be stripped from the building footprint.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1)
soils should be designed for an allowable bearing pressure of 2,000 psf.
Based on
Kumar & Associates, Inc. Project No. 19-7-190
4
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 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) All topsoil, sand and silt and any loose or disturbed soils should be removed and
the structural fill bearing level extended down to the relatively dense natural
granular soils. The structural fill should be compacted to at least 98% of standard
Proctor density at near optimum moisture content. If water seepage is
encountered, the area should be dewatered before fill placement.
6) A representative of the geotechnical engineer should observe all excavations prior
to structural fill placement and should observed structural fill placement on a part
time basis.
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 arc 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
granular soils or imported granular materials.
Kumar & Associates, Inc. Project No. 19-7-190
--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 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 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 granular material compacted to at least
95% of the maximum standard Proctor density at a moisture content near optimum.
SLABS -ON -GRADE
Existing fill, topsoil and silt and sand soil should be stripped from building and driveway areas.
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
Kumar & Associates, Inc. Project No, 19-7-190
-6 -
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 and
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 granular soils devoid of vegetation, topsoil and oversized rock (if any) or imported granular
soils.
UNDERDRAIN SYSTEM
It is our understanding the proposed finished floor elevation at the lowest level is at or above the
surrounding grade. Therefore, a foundation drain system is not required. 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 crawlspace
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall
drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
SURFACE DRAINAGE
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.
Kumar & Associates, Inc. Project No. 19-7-190
7
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.
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 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 pits excavated 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 pits 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.
Kumar & Associates, Inc. Project No. 19-7-190
-8-
Respectfully Submitted,
Kumar & Associates, Inc.
Pwiz"--/z
James H. Parsons, E.I.
Reviewed by:
(
Steven L. Pawlak,
JHP/kac
16222 .'
4s
OF
Kumar & Associates, Inc.
Project No. 19-7-190
/
LOT 6
0.588± ACRES
•
• 5
;o , I
1 .
1
1
sus, • L ; i
f , Nf11
t }'R,
l
n +' 1
A t l � ]
" // \
/ r I ,. 1 i' \ It
/ / . \ ' , I 1
/ PIT 1 \' ` s 1
/ \ ' : 1 ;
ffJ
/ 4'//#
� /\ ; f w
IA
' L .12.03' )
/ ' / ,(�,B.5w12'S '( \� 1
I C -42.0i'
lis."
\ 1
] 11 I/
/ 1 / / :y /\
+;S
\ `rtrn
AWI
FI' �?
A =1374'58 le.
e>
-211.87' �/
L =49.58'
Ca-s5I o2'GrE
\ C =49.45'
\
\
\c
\f COO 2.0' VAR
CORNER C4 S 5 R
4 ORANGE PLA
CAP NCEnLSI
re -M ELEV. exc
y
fr /oa
DP/ELOPE + PIT 2 6 '
,
/
1► /
m, /
/
or sIECETATO[f / .� O NO. S FIJI= E. k
/PROP C IIR sct
A, Islam/ 5\
10 0 10 20
APPROXIMATE SCALE—FEET
FOUND N0. 5 REBA
& YELLOW KAHN
CAD BuEG41:C)
19-7-190
Kumar & Associates
LOCATION OF EXPLORATORY PITS
Fig. 1
1-
w
w
w
— 0
— 5
LEGEND
PIT 1
EL. 6201.5'
WC=42.0
DD=71
–200=55
PIT 2
EL. 6202.5'
1 WC=1.8
1 +4=77
–200=1
TOPSOIL; CLAY AND SILT, SANDY, ORGANIC, FIRM, MOIST, DARK BROWN.
SAND AND SILT (SM–ML); SCATTERED ORGANICS,- MEDIUM STIFF, VERY MOIST, BROWN,
0 —
5
GRAVEL AND COi3ULES (GM–GP); SANDY, SLIGHTLY SILTY, SMALL BOULDERS, MIXED BROWN
AND RED, OXIDi1ED. ROUNDED ROCK.
kHAND DRIVEN 2–INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE.
DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF DIGGING.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 27, 2019.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUND WATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
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).
19-7-190
Kumar & Associates
LOGS OF EXPLORATORY PITS
Fig. 2
ANr p1, Ir. — ce:.oeT
V\! ..+Nx7:+..---.n Pn • Rxss r..l. Lei geCe�rre, rt+:m-cx�
CO
V
O
O O 0 Illi
���av'�oe
e
N°a:9 it
TN
V 1 come
Ei-3
x
'vnno-'m
ipE.��
Om u r7
tlamng
N-.
y m 4 0
Zn_7gmr
C); •
cal
s
s
r-
m
O
7.1
3
`c
G)
G
m
O
O.
X
17
-1
m
v
_
N
®
uA
I
A
r
D
C
-
O-
...7.
-.
En
to
-1
a
1
X
0
s
m
r
V
X
.
0
N
N
N
s
z
o
0
�
(7
5
O
IA
r
rgm
N
m_
m
t
O -
D a,0o
v
at
O o
ae
. t?Np- -..
r"
m
P
-
o
_ -
m
.
PERCENT PAsswe
m o
m
m
m
..
N
O
m
Pi°
xx5
V
Paxp
Z p
_
$
_.._. _ K
:[
— ii
_
7
`g
w
cr • t
L
O
v
0 0
0
HYDR:4ETER ANALYSIS I _ SiEYE ANALYSIS
Kumar & Associates
-_._
I'
m
�-.
S
O
;
D
m
to
s
o
GRADATION TEST RESULTS
---
O
-
O
--
-
w O—
_
Z -
; m `
P
EN,_
PI to.
7d -
+
a-
—
e-
4--
N-
_
=
-
-
V
O
-
O
O
'1
m
~<
(7
O
m
D
m
r
q
-
- \
LI I
0.
O
m m
RI
foo
A
___ - ..
O O S
PERCENT RETAINED
-o
O
Kumar & Associates, inc.
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
ISAMPLE LOCATION
PIT
DEPTH
NATURAL NATURAL
MOISTURE DRY
CONTENT DENSITY
(Y.) (PO
GRADATION
GRAVEL
(%)
SAND
('A)
PERCENT
1 PASSING NO.
200 SIEVE
ATTERBERG LIMITS
LIQUID LIMIT
(%)
PLASTIC
INDEX
UNCONFINED
COMPRESSIVE
STRENGTH
(Pan
Project No. 19-7-190
SOIL TYPE
1
1
42.0
71
55
2
3-4
1.8
77
22
1
Very Sandy Silt with
Organics
Sandy Gravel and Cobbles