HomeMy WebLinkAboutSoils Report 08.28.2019Geotechnical 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
3Yatgov
19-09
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 71, FILING 2, PINYON MESA
PINYON MESA DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-221.01
AUGUST 28, 2019
PREPARED FOR:
PMGC2, LLC
ATTN: RON NORMAN
6300 RIGLEA PLACE, SUITE 900
FORT WORTH, TEXAS 76116
(rmorman@ sbcg1obal.net)
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 - 4 -
FOUNDATIONS - 4 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM 5 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURES 3 and 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc.® Project No. 19-7-221.01
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 71, Filing 2, Pinyon Mesa, Pinyon Mesa Drive, Garfield County, Colorado. The project site
is shown on Figure 1. The purpose of the study was to develop recommendations for foundation
design. The study was conducted as supplemental services to and in accordance with our
agreement for geotechnical engineering services to PMGC2, LLC, dated April 8, 2019.
A field exploration program consisting of an exploratory boring was conducted to obtain
information on 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 subsoil conditions
encountered.
PROPOSED CONSTRUCTION
At the time of our study, design plans for the residence had not been developed. The building is
proposed in the area of the exploratory boring location shown on Figure 1. For the purpose of
our study, we assume below grade levels will not be constructed but there could be a walkout
lower level. Grading for the structure is assumed to be relatively minor with cut depths between
2 and 8 feet. For the purpose of our analysis, foundation loadings for the structure were assumed
to be relatively light and typical of the proposed type of construction.
When building loadings, location and grading plans are available we should be notified to re-
evaluate the recommendations contained in this report.
SITE CONDITIONS
The property was vacant at the time of our exploration. The boring was drilled within the
building area. The site is vegetated with grass, weeds and sagebrush. The ground surface is
Kumar & Associates, Inc. ® Project No. 19-7-221.01
2
relatively flat and slopes moderately down to the north with about 6 feet of elevation difference
across the building area.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. 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, sinkholes have been observed scattered throughout the lower
Roaring Fork Valley. These sinkholes appear similar to others associated with the Eagle Valley
Evaporite in this area.
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 boring was 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 71 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 August 5, 2019. One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
was advanced with a 4-inch diameter continuous flight auger powered by a truck -mounted CME-
45B drill rig. The boring was logged by a representative of Kumar & Associates.
Samples of the subsoils were taken with 1% inch and 2-inch I.D. spoon samplers. The samplers
were 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 and hardness of the bedrock. Depths at which the samples were taken, and the
Kumar & Associates, Inc.® Project No. 19-7-221.01
3
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. Below
about''Y2 foot of organic topsoil the subsoils consist stiff to very stiff, sandy silt and clay with
scattered gravel to the depth explored of 41 feet. Below a depth of about 10 feet, the soils
contained moderately calcareous zones and rock fragments. The soils encountered in the boring
are variable and generally similar to the soils encountered at other nearby lots.
Laboratory testing performed on samples obtained during the field exploration included natural
moisture content and density, and percent fines (percent passing the No. 200 sieve). Swell -
consolidation testing was performed on relatively undisturbed drive samples of the silt and clay
subsoils. The swell -consolidation test results, presented on Figures 3 and 4, indicate low
compressibility under relatively light surcharge loading and a low to moderate collapse potential
when wetted under constant pressure. The upper silt and clay soils are moderately to highly
compressible under additional loading after wetting. The laboratory testing is summarized in
Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The upper sandy silt and clay soils encountered at expected shallow cut depth tend to settle when
they become wetted.
A shallow foundation placed on the sandy silt and clay soils will have a
high risk of settlement if the subsoils become wetted. It will be critical to the long-term
performance of the structure that the recommendations for surface grading and drainage
contained in this report be followed to limit potential wetting of the bearing soils. The amount of
settlement, if the bearing soils become wet, will mainly be related to the depth and extent of
subsurface wetting. Settlement in the event of subsurface wetting could be 1 to 2 inches and
likely cause building distress. Mitigation methods such as deep compaction, a deep foundation
(such as piles or piers extending down around 35 feet below existing ground surface) or a heavily
reinforced mat foundation designed by the structural engineer can be used to support the
Kumar & Associates, Inc.® Project No. 19-7-221.01
4
proposed house with a lower risk of settlement. Presented below are recommendations for
shallow spread footings and slab -on -grade floor bearing on compacted structural fill. if a deep
foundation or mat foundation is desired, we should be contacted to provide further design
recommendations.
DESIGN RECOMMENDATIONS
FOUN DATIONS
Considcring the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, the building can be founded with spread footings bearing on
compacted structural fill with a risk of settlement and possible building distress.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1)
Footings placed on at least 3 feet of compacted structural fill 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 settlement on the order of 1 to 2 inches or
more could occur if deep wetting of the subsoils were to occur.
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 a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
55 pef for the onsite soils as backfill.
5) The topsoil and any loose or disturbed soils should be removed in the building
area. The natural silt and clay soils or silty sand soils in footing areas should be
sub -excavated to at least 3 feet below design bearing level and to at least 11/2 feet
Kumar & Associates, Inc. ® Project No. 19-7-221.01
5
beyond footing edges. The exposed soils in footing area should then be
moistened and compacted. Structural fill can consist of the onsite silt and clay
soils compacted to at least 98% of standard Proctor density at near optimum
moisture content.
6) A representative of the geotechnical engineer should conduct compaction testing
during structural fill placement and observe all footing excavations prior to
concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on -site soils, exclusive of topsoil, can be used to support lightly loaded slab -on -grade
construction with a risk of settlement similar to that for spread 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 interior 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 silty soils or a suitable imported granular soil 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 basement areas be protected from wetting and
hydrostatic pressure buildup by an underdrain system. Slab -on -grade areas and crawispaces less
than 4 feet deep should not be provided with an underdrain.
Kumar & Associates, Inc. ° Project No. 19-7-221.01
6
Where needed, 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. Free -draining granular material used in the
undcrdrain 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 % 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.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to keeping the bearing soils dry
and limiting potential for building settlement and distress. 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 (if any)
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.
Kumar & Associates, Inc.® Project No. 19-7-221.01
7
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
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 to be different from those described in this report, we should be
notified at once so 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 of 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.
Sincerely,
Kumar & Associates, Inc.
Shane J. Robat, P.E.
Reviewed by:
Steven L. Pawlak,
SJR/kac
cc: Integrated — S
cdil lardrea! tor0,grnail.com)
Kumar & Associates, Inc.
Project No. 19-7-221.01
20 0 20 nc
APPROXIMATE SCALE —FEET
LOT 72 1� / /
r \
i /
` . 1
r / e \
/ , r/ \.
N'• /'%. BORING 1/71 \
0 \
X
LOT 71
- /
\, -
--1
/ /-
1
‘ ..__- ..._ -..-
� „---
LOT 70
1 �Fr
1 1 /
I /
1
/
I /
1
1
1
1
I 1 /
/ F
/
\rr
.
V' r- LOT 69
•
/'
LOT 68
19-7-221.1
Kumar & Associates r LOCATION OF EXPLORATORY BORING
Fig. 1
DEPTH -FEET
BORING 1/71
0
- 12/12
/ WC=6.8
- f DD=97
5] 10/12
WC=8.8
T DD=94
/ -200=87
10 /
/ 1 32/12
- 15
JJ 18/12
WC=5.9
DD=105
20 r ��a 16/12
/f
25 • 11 29/12
✓ WC=4.8
DD=108
-200=75
//
---- 30
�26/12
'- WC=8.2
/ DD=110
f f-200=85
35
40 f
Al 32/12
19-7-221.1
LEGEND
oisz
r
TOPSOIL; SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST,
DARK BROWN.
SILT AND CLAY (ML—CL); SLIGHTLY SANDY TO SANDY,
SCATTERED GRAVEL, STIFF TO VERY STIFF, SLIGHTLY MOIST,
LIGHT BROWN, SLIGHTLY POROUS, MODERATELY CALCAREOUS
ZONES BELOW 10 FEET.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH SPLIT SPOON STANDARD
PENETRATION TEST.
5/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 5 BLOWS OF
A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED
TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORING WAS DRILLED ON AUGUST 5, 2019
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.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT
MEASURED AND THE LOG OF THE EXPLORATORY BORING IS
PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATION 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).
Kumar & Associates
LOG OF EXPLORATORY BORING
Fig. 2
1
0
1 —2
Z
O
c) — 4
'
I
I
SAMPLE OF: Sandy Clay and Silt
FROM: Boring 1 /71 ® 2.5'
WC = 6.8 %. DD = 97 pcf
f
I
ADDITIONAL
UNDER
DUE
CONSTANT
TO
I
COMPRESSION
WETTING
PRESSURE
I
I
11
I
I
Th.. us, Penang op* only to the
i no..pThuuptpotn
full. withoutthe written approval of
lWmor and ,1ppnl.tee, Inc. Swell
Cneo do naRh UASpe—wMIn
1 0
APPUED PRESSURE — KSF 10
to
0
19-7-221.1
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
Fig. 3
CONSOLIDATION - SWELL
Thew Sit rpulh appy only to the
eemproe looted. The tiding report
ehen net be reproduced, 'motel In
tuII. wltheut the trillion opproval of
IKumor and Aeedclotee, Inc. Swell
1Coneoildellon letting performed In
accordance etlh ASTM 0-4 45.
1
10
SAMPLE OF: Sandy Clay and Silt
FROM: Boring 1/71 ® 15'
WC = 5.9 %, DD = 105 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
APPLIED PRESSURE — KSF 10 10o
19-7-221.1
Kumar & Associates
SWELL —CONSOLIDATION TEST RESULTS
Fig. 4
K±A
Kumar & Associates, Inc.
GeorEchnical and Materials Engineers
and Envionmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 19-7-221.01
Lot 71
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(PO
GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
S—HENGTH
(Psfl
I
SOIL TYPE
BORING
DEPTH
(tt)
GRAVEL
n
(%)
SAND
(%)
1 LIQUID LIMIT
(%)
PLASTIC
INDEX
i%)
1/71
2Y2
6.8
97
' Sandy Clay and Silt
5
8.8
94
87
Sandy Clay and Silt
15
5.9
105
Sandy Clay and Silt
25
4.8
108
75
Calcareous Sandy Clay and
Silt
30
8.2
110
85
Sandy Clay and Silt