HomeMy WebLinkAboutPreliminary Geotechnical Study and Geological Hazards Review 10.17.17H.PVKUMAR
Geotedrnlcal Engineedng I Englneering Geology
Materlals Testing I Environmentral
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 Summit County, Colo¡ado
PRELIMINARY GEOTECHI\IICAL ENGINEERING STUDY
AND GEOLOGIC HAZARDS REVIEW
PROPOSED MOUNTAIN SHADOW MINOR ST]BDIVISION
MOUNTAIN SHADOWS DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 17.7-728
ocToBER 17,2017
PREPARED FOR:
DAVID RASMUSSEN DESIGN
ATTN: DAVID RASMUSSEN
826C HIGHWAY 133
CARBONDALE, CO 81ó23
david @ davidrasmussendesi gn.com
RECEIVED
FEB 0 4 2019
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED DEVELOPMENT
...- I -
.....- I -
SITE CONDTTIONS ......
GEOLOGIC SETTING.
FIELD EXPLORATION
SUBSURFACE CONDITIONS
GEOLOGIC SITE ASSESSMENT.....
HYDRO-COMPRESSIVE AND COLLAPSIBLE SOILS
SUBSIDENCE POTENTTAL.........
RADIATION POTENTIAL,..........
EARTHQUAKE CONSTDERATTONS .......
PRELIMINARY DESIGN RECOMMENDATIONS
FOIINDATTONS
FOUNDATION AND RETAINING V/ALLS .....
FLOOR SLABS
UNDERDRAIN SYSTEM ......
SURFACE DRAINAGE
LIMITATIONS....,.
REFERENCES ......
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 THROUGH 6 - SWELL-CONSOLIDATION TEST RESULTS
FIGURE 7 - GRADATION TEST RESULTS
FIGURE 8 - REGIONAL GEOLOGY MAP
FIGURE 9 - WESTERN COLORADO EVAPORITE REGION
FIGURE 10. GEOLOGICALLY YOUNG FAULTS AND LARGER HISTORIC
EARTHQUAKES
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
-2-
-2-
4
5
5
6
7
7
8-
-8-
_o_
............- 10 -
11-
11-
-1t -
.............- 13 -
H-P*¡¡¡¡y¡p
Project No.17-7-728
PURPOSE AND SCOPE OF STUDY
This report presents the results of a geologic hazards review and preliminary geotechnical
engineering study for the proposed Mountain Shadow Minor Subdivision to be located at the
west end of Mountain Shadows Drive, Garfield County, Colorado. The project site is shown on
Figure 1. The purpose of the study was to evaluate the geologic and subsurface conditions and
their potential impact on the project. The study was conducted in accordance with our agreement
for geotechnical engineeiing services to David Rasmussen Design, dated September 28,2017.
A field exploration program consisting of exploratory borings and field reconnaissance was
cunducted to obtain information on the subsurface and site conditions. Samples of the subsoils
obtained during the field exploration were tested in the laboratory to determine their
classification, compressibility and swell, and other engineering characteristics. The results of the
field exploration and laboratory testing were analyzed to develop preliminary recommendations
for foundation types, depths and allowable pressures for the proposed building foundations. This
report summarizes the data obtained during this study and presents our findings,
recommendations and other geotechnical engineering considerations based on the proposed
construction, subsurface conditions encountered and geologic conditions observed.
PROPOSED DEVELOPMENT
The proposed development will consist of a 3-lot subdivision for single family homes as shown
on Figure l. A private driveway will access the building sites from the north, off of Mountain
Shadows Drive. We assume the residences will be typical of the area and be one- to two-story
structures with walkout basements. Ground floors will probably be slab-on-grade. Grading for
the structures is assumed to be relatively minor with cut depths up to about 8 to l0 feet. We
assume relatively light foundation loadings, typical of the proposed type of construction. The
development will be serviced with municipal water and sewer systems.
If development plans change significantly from those described, we should be notified to re-
evaluate the recommendations presented in this report.
H.PèKU¡VIAR
ProJecl No.17-7-728
-2
SITE CONDITIONS
The proposed subdivision consists of about 0.833 acres located in the SESW Section 11, T5S,
R89W. The project site is cunently vacant of structures. There is a gravel driveway that leads to
the proposed building sites from Mountain Shadows Drive. Lots 1 through 3 are located to the
south of the gravel drive. The proposed building sites are on a moderate to gently sloping
alluvial fan. The building sites generally slope down to the south at less than 5 percent. The
northwest part of the site slopes down to the south at around 30 percent. There is a small boulder
wall on the south edge of the property. The vegetation at the project site consists of grass,
weeds, and brush. The site is bordered to the south by a seasonally active irigation ditch. There
appears to be up to I feet of fill material on the south portion of the property above the boulder
wall.
GEOLOGIC SETTING
The main geologic features in the project areaare shown on Figure 8. This map is based on the
published regional map by Kirkham and Others (2009).
The project site lies on the northern edge of the valley formed by the Colorado River just west of
Glenwood Springs. The lower, northern valley side is predominately covered in colluvial
deposits ranging from early Pleistocene to late Holocene in age (QIs, Qt, ec, edfo, eaco, eac,
and Qdfy). The valley bottom is covered in middle to late Pleistocene-age terrace alluvium from
the Colorado River (Qto and Qty). The curent Colorado River is bordered by stream channel,
flood plain, and low-terrace alluvium (Qa). Tufa deposits (Qtu) exist in the area near naturally
occuring hot springs. Tufa is porous calcium carbonate that has precipitated out of the spring
water. The formation rock in the area consists of the Læadville Limestone (Ml), The Beldon
Formation (Pb), the Eagle Valley Evaporite (Pee), the Eagle Valley Formation (Pe), and the
Maroon Formation (PPm). The Mississippian-age læadville l-imestone is a grayish limestone
with intermixed dolomite. The l¡wer Pennsylvanian-age Beldon Formation is a gray to black
shale with interbedded limestone and fine-grained sandstone. It is generally calcareous and can
contain gypsum, The Middle Pennsylvanian-age Eagle Valley Evaporite is a sequence of
H.PIKUMAR Project No.17-7-728
-3-
evaporitic gypsum, halite, and anhydrite interbedded with shales, mudstones, and fine-grained
sandstones. The Middle Pennsylvanian-age Eagle Valley Formation is a transitional material of
the evaporitic rocks of the Eagle Valley Evaporite to the younger clastic rocks of the Maroon
Formation. The Pennsylvanian- and Permian-age Maroon Formation consists of reddish
interbedded claystone, mudstone, sandstone, and conglomerate. Bedding of the formation rock
in the area generally dips down to the southwest at angles between around 30 to 60 degrees.
The project site is located on the northern edge of the Carbondale Collapse Center. The
Carbondale Collapse Center formed in the late Cenozoic due to evaporite tectonism. The Eagle
Valley Evaporite migrated plastically upwards and laterally toward the Colorado River and
Roaring Fork River bottoms due to a reduction in vertical stress caused by the erosion of
overburden material by the rivers. Subsidence occuned in areas of the thinned evaporite and
beneath the rivers due to dissolution (Kirkham, and Others, 2003). Much of this subsidence
appears to have occurued within the past 3 million years which also corresponds to high incision
rates of the Roaring Fork and Crystal Rivers (Kunk and Others, 2002). It is uncertain if the
regional subsidence is still an active geomorphic process or if evaporite subsidence has stopped.
If still active, present deformations may be occurring at rates similar to past long-term rates of
between 0.5 and 1.6 inches per 100 yeÍus. These slow deformation rates should not present a
potential risk to the proposed subdivision aÍea.
The project site is underlain by Quaternary Younger Debris Flow Deposits (Qdfy) overlying
Quaternary Younger Temace Deposits (Qto). The Eagle Valley Evaporite or Eagle Valley
Formation underlies the project site at depth. The Quaternary Younger Debris Flow Deposits
consist of silty gravel and sand with cobbles that is matrix supported clayey sand and silt with
scattered gravel and cobbles. The material could be hydro-compressive and/or collapsible.
FIELD EXPLORATION
The field exploration for the project was conducted on September 28,zÙn. Three exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
H-PtKUMAR Project No.17-7-728
-4-
The borings were advanced with 4-inch diameter continuous flight augers powered by a
truck-mounted CME-458 drill rig. The borings were logged by a representative of H-P/Kumar
Samples of the subsoils were taken with l% 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, 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.
The field reconnaissance for the geologic hazardreview was conducted on September 29,Z0I7
ST]BSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist ofabout nil to I foot oftopsoil overlying around 17 to2l feet ofsand and silt
with gravel underlain by sandy silt with gravel to the maximum clepth explored of 30 feet in
Borings I and 3. Boring 2 was advanced to a depth of 46 feet with dense river gravel
encountered at a depth of 40 feet. Two feet of fill from prior site development \ /as encountered
at the surface in Boring 3.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density, and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples, presented on Figures 4 through 6, generally indicate low to
moderate compressibility and low to moderate collapse potential under contlitions of loading and
wettlng. A sample from Boring I at')tJ t'eet in depth (Figure 4) showed low compressibility
under a light surcharge and minor swell potential when wetted. Results of gradation analyses
performed on small diameter drive samples (minus lVzinchfraction) of the coarse granular
subsoils are shown on Figurc 7. The laboratory testing is summzuized in Table l.
H.P*KUMAR Project Na.17-7-728
-5-
No free water was encountered in Lhe horings at the time of drilling and the subsoils were
slighf.ly ¡noist to moist with depth.
GEOLOGIC SITE ASSESSMENT
The project site geology should not present major constraints or unusually high risks to the
proposed development. There are, however, several conditions of a geologic nature that should
be considered. Geologic conditions that should be considered, their potential risks, and
mitigations to reduce the potential risks are discussed below. The site could experience
moderate levels of earthquake related ground shaking. Foundation bearing conditions at building
sites should be evaluated by site-specific geotechnical engineering studies as project planning
and design proceeds for the individual lots.
HYDRO-COMPRESSTVE AND COLLAPSIBLE SOILS
The slightly clayey silty sand matrix supported gravel and cobbles and clayey sand and silt soils
encountered at the site tend to settle when they become wetted. A shallow foundation placed on
the matrix supported and sandy clay and silt soils will have a risk of settlement if the soils
become wetted and care should be taken in the surface and subsurface drain age around structures
in the proposed development to prevent the soils from becoming wet. It will be critical to the
long-term performance of the structures that the recommendations for surface drainage and
subsurface drainage contained in the site-specific reports be followed. The amount of settlement,
if the bearing soils become wet, will mainly be related to the depth ancl extent of subsurface
wetting. Settlement in the event of subsurface wetting could cause building distress. Mitigation
methods such as deep compaction, a cleep foundation (such as piles or piers extending down into
the dense gravel below the alluvial fan soils) or heavily reinforced foundations designed by the
structural engineer can be used to support the proposed residences with a risk of settlement. The
r+compressr potential of the foundation bearing soils should be evaluated by
site-specific geotechnical engineering studies for the individual lots as proiect planning and
design proceeds
*
H-P!KUMAR Project No.17-7-728
-6-
SUBSIDENCE POTENTIAL
The evaporite mineral in the Eagle Valley Evaporite can be locally soluble in circulating
groundwater and solution of these minerals can result in local subsurface voids which can
sometimes develop into surface sinkholes. Shallow subsurface solution voids and sinkholes are
locally present in areas where the evaporite lies at a shallow depth throughout the western
Colorado evaporite region, see Figure 9. The general character of evaporite sinkholes and the
potential risk that sinkholes pose to the proposed site are discussed below.
General Character of Evaporite Sinkholes
Evaporite sinkholes in western Colorado are typically 10- to S0-foot diameter, circular
depressions at the ground surface. The sinkholes mostly result from upward caving of a soil
rubble pipe to thc ground surface. The soil rubble pipe is fonnecl hy piping ancl subsurface
erosion of surficial soils into subsurface solution voids in the underlying evaporite. Direct
caving ofvery large solution caves has also occurred in the region. New sinkholes can develop
at the ground surface with little or no advanced warnings and existing sinkholes can be
reactivated. New sinkholes and reactivated sinkholes have the potential for severe damage to
buildings and other man-made facilities. Historic sinkholes have developed in the western
Colorado evaporite region but have rarely damaged structures. This indicates that sinkhole
development is still an active geomorphic process in the region but does not statistically present
an unusually high risk to structures in the region as a whole.
Potential Sinkhole Risk
Evidence of sinkholes was not observed in the field or on the aerial photographs of the project
site. In our opinion, the risk that a sinkhole will develop at the proposed subdivision site is low
during a reasonable exposure time. The sinkhole risk at the project site does not appear greater
than the existing risk elsewhere in the Roaring Fork River valley or in the western Colorado
evaporite region with shallow evaporite, as shown on Figure 9. The low risk in the region is
inferred from the large extent of the sinkhole prone areas in comparison to the small number of
new sinkholes that have developed during historic times in the region. The project site owner
should be made aware of the low sinkhole risk and that the proposed facilities cannot be
considered totally risk free. If evidence of a developing sinkhole is notcd, it may be possible to
H-PvKUtvlAR Project No. 17-7-728
-7 -
limit potential facility tlanuge with gmuntl inrprovement techniques such as structural backfill
and compaction grouting.
RADIATION POTENTIAL
The project site is not located on geologic deposits that would be expected to have high
concentration of radioactive minerals. However, there is a potential that radon gas could be
present in the area. It is difficult to assess future radon gas concentrations in buildings before the
buildings are constructed. Testing for radon gas levels could be done when the residences and
other occupied structures have been completed. New buildings are often designed with
provisions for ventilation of lower enclosed areas should post construction testing show
unacceptable radon gas concentration.
EARTHQUAKE CONSIDERATIONS
Historic earthquakes within 150 miles of the project site have typically been moderately strong
with magnitudes less than 5.5 and maximum Modified Mercalli Intensities less than VI, see
Figure 10. The largest historic earthquake in the project region occured in 1882. It was locatecl
in the northem Front Range and had an estimated magnitude of about M6.2 x.0.3 and a
maximum intensity of VII. Historic ground shaking at the project site associated with the 1882
earthquake and the other larger historic earthquakes in the region does not appear to have
exceeded Modified Mercalli Intensity VI (Kirkham and Rogers, 1985). Modified Mercalli
Intensity VI ground shaking should be expected during a reasonable exposure time for the
residence, but the probability of stronger ground shaking is low. Intensity VI ground shaking is
felt by most people ancl caused general alarm, but results in negligible damage to structures of
good design and construction.
The U. S. Geological Survey 2014 National Seismic Hazañ Maps indicates that a peak ground
acceleration of 0.079 has a lOTo exceedance probability for a 50-year exposure time and a peak
ground acceleration of 0.209 has aTVo exceedance probability for a 50-year exposure time at the
project site (Peterson and Others, 2014). This corresponds to a statistical recurrence time of
H-PIKUMAR Project No.17-7-728
-8
about 500 years and 2,500 years, respectively. These acceleration s are for firm rock sites with
shear wave velocities of 2,500 fps and higher in the upper 100 feet and shoukl be modified for
soil profile amplification at the project site. The seismic soil profile at the project site should be
considered as Class D, stiff soil sil¿s as described in the 2015 International Building Code unless
site specific shear wave velocity studies show otherwise.
PRELIMINARY DESIGN RECOMMENDATIONS
The conclusions and recommendations presented below are based on the proposed development,
subsurface conditions encountered in the exploratory borings, and our experience in the area.
The recommendations are suitable for planning and preliminary design but site-specific studies
should be conducted for individual lot development.
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, spread footings or structural slab bearing on the natural soils can be
used for the support of foundations in the proposed subdivision with a risk of settlement. If a
deep foundation or deep compaction is desired to reduce the settlement risk, we should be
contacted for additional recommendations.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings or structural slab placed on the undisturbed natural soils should be
designed for an allowable bearing pressure of 1,200 psf. Based on experience, we
expect initial settlement of footings designed and constructed as discussed in this
section will be about I inch or less. Additional settlement of about I inch could
occur depcnding on the depth and extent of pust-construction wetting and
precautions should be taken to keep the bearing soils dry.
2) The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolatecl pads.
H.PèKUIVIAR Project No. 17-7-728
-9-
3)Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
offoundations at least 36 inches below exterior grade is typically used in this
area.
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.
The topsoil, existing fill, and any loose or disturbed soils should be removed and
the footing bearing level extended down to the natural soils. The loosened soils in
footing area should then be moistened and compacted.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
4)
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. Cantilevered retaining structures which are separate from the
structures and can be expected to deflect sufficiently to mobilize the full active earth pressure
condition should be designed for a lateral earth pressure computecl on the basis of an equivalent
fluid unit weight of at least 4O pcf for backfill consisting of the on-site granular soils devoid of
vegetation, topsoil and oversized (plus 6-inch size) rock.
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
s)
6)
H.PèKUMAR Project No.17-7-728
- 10-
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 gOVo of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in pavement and
walkway areas should be compacted to at leastg1%o 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 350 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of sat'ety 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 shoulld be a granular material compacted to at least
957o uÏ. the maximum ståndard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil and pre-existing fill, should be suitable to support
lightly loaded slab-on-grade construction. There is a risk of settlement and distress if the bearing
soils are wetted. 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-
H.PIKUIVIAR Project No.17-7-728
- 1r -
draining gravel should be placed beneath basement level slabs to facilitate drainage. This
material should consist of minus 2-inch aggregate with at least 5O7o retained on the No. 4 sieve
and less than2Vo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 957o 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 (plus 6-inch size) 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. Shallow crawlspace
areas should not need a subdrain with proper grading and compaction of foundation wall
backfill.
The drains should consist of drainpipe placed in the bottom of the wall backfill surounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum l7o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Vo passing the No. 200 sieve, less than 507o passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least lVzfeet deep. An
impervious membrane such as 30 mil PVC should be placed beneath the drain gravel in a trough
shape and attached to the foundation wall with mastic to prevent wetting clf the bearing soils.
SURFACE DRAINAGE
Providing proper grading and drainage around the structures will be critical to limiting
subsurface wetting and potential building movements. The following drainage precautions
H.PlKUIVIAR Project No.17-7-728
-L2-
should be observed during construction and maintained at all times after the construction has
been cornpleted:
1) Inundation ofthe 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 957o of fhe maximum standard Proctor density in pavement and slab areas
and to at least 90Vo of the maximum standard Proctor density in landscape areas.
3) The ground surface sunounding 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 finer graded
soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill. \ Aleo roôe o{^rt^.â^^4all.
5) Landscaping which requires regular heavy inigatioi should be located at least l0
feet from foundation walls. Consideration should be given to use of xeriscape to
limit potential wetting from landscape inigation.
I,IMITATIONS
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 preliminary recommendations submitted in this report are based upon our
field observations, aerial photograph interpretations, published regional geology information, the
data obtained from the exploratory borings drilled at the locations indicated on Figure l, 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 lìndings include interpolation and
extrapolation ofthe subsurface conditions identified at the exploratory borings and variations in
H.PIKUÍVIAR Projecl No. 17-7-728
-13-
the subsurface conditions may not become evident until additional subsurface exploration for the
individual lots or excavation is performed. If conditions encountered during additional
excavations 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 planning and preliminary
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,
I.I-PTKUMAR
l"r-"*L
Robert L. Duran, E.I
Reviewed by
Steven L. Pawlak, P
RLD/kac
REFERENCES
Kirkham, R., M., Streufert, R. K., Cappa, J. .A., Shaw, C.A., Allen, J.L., and Schroeder, T.J.II.
2009, Geologic Map of the Glenwood Springs Quadrangle, Garfield County, Colorado:
Colorado Geological Survey Map MS-38.
Kirkham, R. M. and Rogers, W. P., 1985, Colorado Earthquake Data and Interpretations i,867
to 1985: Colorado Geological Survey Bulletin 46.
'1-
IT
H.PVKUIVIAR Projecl No. 17-7-728
-t4-
Kirkham, R.M., white, J. L., sares, M. 4., Mock, R. G., and Lidke D. J., 2003, Engineering and
Environmental Aspects of Evaporite Karst in West-Central Colorctdo in Johns, K. S., and
Neal, J. T. (eds), Evapuril"e Karst and EngineeringÆnvironmental Problems in the United
States: Oklahoma Geological Survey Circular 109, p. 279-292.
Kunk, M., J., and Others, 2002,40Ar/39Ar Ages of Late Cenozoic Volcanic Roclcs wíthin and
Around the Carbondale and Eagle Collapse Centers, Colorado: Constrøínts on the
Timing of Evaporite-Related Collapse and Incision of the Colorado River,in Kirkham R.
M., Scott, R. 8., and Judkins, T. W. eds., Late Cenozoic Evaporite Tectonism and.
Volcanism in West-Central Colorado: Geological Society of America Special Paper 336,
Boulder, Colorado.
Peterson, M. D. and Others, 2014, Docunrcntation for the 2014 Updare of the National Seisntic
Hazard Maps: U. S. Geological Survey Open-Ëìle Report ZOl4-l0gI.
Widmann B. L. and Others, 1998, Prelinr,inary Quatemary Fault and fi'otd Map and Data Bøse
of Colorado: Colorado Geological Survey Open-File Report 98-g.
H-PvKJIWqR Project No.17-7-728
.0 {
67¿08¡ü
t-
r
r
, -tt- -
I
I
-S-
l-'-/\:f*-*
Ãttnt À'^
at -fr-(
V .->/r-
--þ-'y'^'-
-5*
II z'-\ 1;->--f-I
2t¡¡9
47U970¡3
67¡r 4{?8
L@1øu
¿986
x 3I492t¡
APPROXIMATE SCALE-FTEÏ
r
5Lo1
BORING 3
,'BoRlNGI
¡
I
-'-{
z\\l
Lol
17 -7 -728 H-PryKUMAR LOCATION OF IXPLORATORY BORINGS Fig. 1
I
E
:
z:
¡
BORING f
EL. 5790'
BORING 2
EL. 5783'
BORING 3
EL. 5786'
0 ü
25/ 12 23/12
26/ 12
WC=3.2
DD=113
-2Oô=37
5 530/ 12
WC=4.4
ÐÐ=122
- 200=33
28/12
WC=5.5
DD='l I 7
-200=5 1
42/12
10
s5/12
WC=3.2
DD=97
+4=36
-2OQ=32
1018/ 12
WC=5.1
DD= 1 04
21/12
t5 15e/6,50/ 4 22/6,5o/5 41112
lYC=2.5
+4=41
-200=3 1
20 20
l-
L,J
UJt!
I-l-
L!ô
31/12
WC=5.5
DD=116
-ZQO=72
23/12
WC=6.8
DD= J 09
241 12 Fl¡J
l¡Jt!
I-l--
IL
L¡Jô
25 25
3s /12 63/12
WC=3.6
DD-116
-200=36
50 30su/\2 22/12
WC=8.0
DD=1 1 1
-200=81
37 /12
35 35
40 40
45
50/6 45
17 -7 -728 H.PryKUMAR LOGS OF EXPLORATORY BORINGS Fig. 2
LEGEND
N
m
m
TOPSOIL; SILT AND CLAY, SANDY, ORGANIC, M0|ST, DARK BROWN.
FILL; GRAVEL AND CLAY, SANDY, SILTY, SLIGHTLY ORCANIC, FIRM, MO|ST, BROWN
GRÀVEL AND SAND (CM-SM)¡ WITH COBBLES, SILTY, SLIGHTLY CLAYEY, SOME SANDy SILT
AND CLAY LAYERS, MEDIUM DENSE, SLIGHTIY MOIST, MIXEO TAN, SUBANGULAR TO
SUBROUNDED, MATRIX SUPPORTED.
!L{g {N?-.ll!l (ly:t¡Ði cLAyEy, SCATTERED GRAVELS AND coBBLEs, MED|UM DENsE/vERy
SÏIFF, SLIGHTLY MOIST TO MOIST, TAN.
COBSLES AND GRAVEL (GP-GM); SANDY, SLIGHTLY slLTY, DENSE, MotST, MIXEÐ BROWN,
ROUNDED ROCK.
F
I
RELATIVTLY UNDISTURBEO DRIVE SAMPLE; 2-INCH l.Ð. CALIFORNIA LTNER SAMpLE.
oRlvE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH t.D. sPLtT spooN
SAMPLE, ASTM D-I586.
2c,¡17 DRTYE SAMPLE BLOW COUNT. INDICAIES THAT 25 BLOWS OF A 140-POUND HAMMER.-,.- FALLING 30 INCHES WERE REQUIRÊD TO ORIVE THE CALIFoRNIA oR SPT SAMPLER 12 INCHES.
NOTES
THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBÊR 28, 2017 WITH A 4_INCH DIAMETER
CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY 8Y PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINEO BY INTERPOLATION EETWEIN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE OEGREE IMPLIED BY THE METHOD USÊD.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIÊS BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY 8E GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THT TIME OF DRILLING.
7, LABORATORY TEST RESULTS:wc = WATER coNrENr (%) (ASTM Ð 2216)¡
DD = ÐRY DENSITY (PCf) (ASTM D 2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVÊ (ASTM D 422)i
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140).
17-7-728 H-PVKUMAR LEGEND AND NCITTS Fig. 3
!
SAMPLE OFr Sondy Sllt ond Cloy
FR0M;loring1O20'
WC = 5.5 %, DD = 116 pcf
-29Q = 72 %
i:'i
ti:
EXPANSION UNOER CONSTANT
PRESSURE UPON WETTING
I
!i
¡
I
I
I
jl,,
¡
I
;
I
:
I
I
I
:I
).1
'I
..-",i
¡
ll
._..i
.liitliì
N
4t
l¡J
=U'
lo
2otr
ô
=-lovlzo(J
I
t7 -7 -728 H-PTKUIVIAR SWELL-CONSOLIDATION TEST RESULTS Fis. 4
fI
I
t
!¡
¿
SAMPLE OF: Silty Sond wilh Grovet
FROM: Boring 2@ 10'
WC=5.1 %,ÐD= f04pcf
ÀDDITIONAL COMPRESSION
UNDER CONSTÅNT PRESSURE
DUE TO WETTING
2
0
-2
J-¿
1¡l
=ø
I16
()
tr
!-ao
u7zoo -lo
-12
1.0 ÂPPLIEO
17 -7 -728 H-PVKU]VIAR SWELL-CONSOLIDATION TTST RTSULTS Fig. 5
SAMPLE OF: Sondy Silt
FROMrBoring2O20'
WC = 6.8 %, DD = 109 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
ÐUE TO WETTING
I
-.i -:
ti
i,.
i:
ll
l,
'
I
:
1
I
I
I
I
l
:
lr
l!
¡
:::
I
- KSF t00
1
0N
t- -1l,
=tf,
t-z
zoË
t-soltlzoQ_1
17-7-728 H-PâTKUTVIAR SWTLL-CONSOLIDATION TEST RTSULTS Fig. 6
g
HYOROMÊÎER ANALYSIS SI:VE ANALYSIS
IIT¿ REAÞIXıI
¡4 flil t xñs¿4 !r¡ 1¡
u.5. tso no ttitÊs
SAND GRAVEL
FINE MEDIUM FINE COARSE
ã
F
too
¡o
!0
,o
60
50
6
50
20
t0
o
0
to
20
to
1t)
t0
ao
70
to
¡0
t
E
I
DIAM OF
CLÂY TO SILT COSBLES
GRAVET 56 '¿ SAND
LIQUID IIMIT
SAMPLE 0F: Sllly Sond qnd Grovll
327
PtasTtctw tNDgx
SILT ANO CLAY 32
'(
FROM:Sorlngtet0'
t
3
HÊ
tm
¡o
lo
,o
æ
s
ß
lo
20
lo
o
to
zo
l0
s
s
&
10
t0
¡o
t00
I
E
Þ
v
Ë
IN MI
CLAY TO SILÏ SAND
COBBLES
GRAVEL 11 X SAND
LIQUIO LIMIT
SAMPLE OF: Sllty Sond ond crov.l
28X
PTASTICITY INDEX
SILI AND CLAY
'1
X
FROII:8oring3O15'
fùq. l..l ðruth oppt onlt to th.r(npl.¡ rhloh r.r. hrhd. fh.l..llng rupgrl.holl nol b. r.DÞduc.d,.¡caÞl ln lull, rlthosl lh. rrftl.ndppEwl ol Kumqa & Artoc¡oLr, lnÉ.Slry. qnolytl¡ lqtlñ! lt grlcm.d Inoccord.nct rllh ¡Sn/ 0422. Asll¡ Ct38
ond¡lo. ¡Sll¡ Dtl/to,
ITYOROMSTER ANÀLYSIS stEvE Ai¡ALYSTS
lva Rrur¡Gs
¡a NRS t HiS
sgnßs
- -: : - ì :l.
:,:.
'. .:
GRAVEL
FINE MEDIUM FINE COARSE
17 -7 *728 H-PryKUMAR GRADATION TTST RESULTS Fi1. 7
It
\
..¡
ï
þls
-tff
-.'-i I ¡
t
1
oËfg
t
'i -i< ¡f
t*u ';tt
/iF4"- :
Qgç¡-1''-
.:l':
I
-'f.
{ì'ht.".
¡
./l
.t
0c\;':Ixrt "\-
r
Odlo
Qtv s
Qa
t,l:¡"
lr -t'
r I JrI
.'\
tI
G*
aa/' '
Odfy t.'
.-"
1._
0.6 MIêS/h
ffi
l¡qL t ¡ó¡ l.ìrFn4 1$¿lb lñath.ù',¡r, .¡,ra.
¡, {ls , .: ¡r{ rr ..1? ¡Þ.r fl-Lr.rl
-:1.j:'i.l 4ii. f, I ¡.r in! r. !:r!¡ -: .' !ù,ll¡r
. nrr.!'. :t, nt¡ 1ba û irÞ{'.I Sr{1, . r ,. r,ri¡ d t' , . .n r| ,!{.r
G ktr .ïù!ùr {-rÉrr ¡*br!un:ñr,¡!, I t,! r. ¡
,. 1 ts, .rl..,r, ,l , ., .: . . ,..,. i-.
. '1 .i: tt i' _¡ Á!s:i':'- !
. ilr¡!, r.u I ni¡qìet. :,,!i.
ú lr¿À;irr r,e¿lnl i!¡ú.¡r4!,ù* 1 r-,, ù, - ¡ Èrt+ tj.: ìc l'.e
ìÞ,,-i."¡ \rt ..,rfÈ --r.,,1.rr- .i-¡
:'-- - te¡-! ò,nt':rtfr'.¡i$¡! h.¡!r ¡rar,d,.>-,.
nr¡r È{,lir ¿É Þ:,r,ihdnn!¡i&
L¡r ] {$dr d br? .d'4! ılbgÉ ¡Þ ..,¡11ç¡ . Þ:l
c.r ,Þ. ÉnÞ r;r.r .i.ri-: q!¿r. ¡íJ,vrlr .
.rki 4.!id {$!. trF-rrìàr !\.trl¡ì¡,}
*1!r'i,n! ia{r¡. :11 ¡* !*n¡. \r¡. r ¡
hñ6r lr:rqr!1 ìì: !' t tiry.-
*¡k d dF d U* b¡r ,1 ,¡r {ríf, ú, ¡¡ì,ra
rÞÊ{rr.ù;* .t i.¡:: n..¡ :,&rÅ,- k¡ ri it'?
tdt¡ù¡
l,!ñSù J6¡h.fu* d@h illd.cd4-{rrrh {sil I
ÞV,t,,qlr ¡'ÉûL.r '!rqr ,r¡ .U{e¡j;r.}J,
Þdl4; I'A-" ¡¡l * r ¡¡,.: r, r e:¡r ù d 'ir'ied r!5.. l*,14:a?.i.*¡ : \,S¡::rú tt;rr:î.,
4t¡s1i!ñ rnd d{lþr'&s- vdiri&a l¡ÁFr^f ¡d ld4r?$lr¡er-Àlhlf¡¡r'Þ \rrl¡¡u,.J Ð e<li {rtdsnrú, hrhùd sù1 Fl¡;' $!, ¡* Ðal
ç,!.1r. i+-rk1:&i q: !r_Ù .i!rt\ùì. rrnlturl¡.ry¡li, ¡.{ \ij*r *ii 1rle.l!çI
t,¡ó¿r lror¡u6 ¡rd rd¡¿'irñ, ùdd¡d iÉdrk6¿...¡\FviF !¡:u.rs( r'-:. lì e' Jl! n-r h: td,;rú¡
'¡rirlJdl-€,r¡r. ,6¡ u¡1. ¡ tha,i fsr å: !4r:
,fur¿ g ù¡rrlk,U!r ajlrr
rll&r &hd,.lì{ç lFdr te ñrinþ. ¡ßd.ù¡r:nei**t*&:d:tr 11 :,v.,ir.rn¿ &Lt 3 ,riÉL.td ' lÈ k,- i.{,¡Þl.i.'{ I,aÊrr¡ l?n*òL À1.\r,; sr ¡,.. ir " t. n;,., ¡.. ...ùB d {r i.rt* . ¡ø?!
{.lldrt¡s llbß.æ jd k€ h(ssFr-\dú..!. nit!.r¿¡rf rd,rÉ:qÈÀ,\, 1r?i:Ìr{ ¡ .:¡ iì^;...-r ¡j\.J! rr" l¡éh ¡
frlñ ttþk.¿. ¡ßúb. rurs¡.rú- \!p{' rì¡ !} ¡r1\q¡lLr'. nt\. k',,*r ,d. ì¡¿-iL ..j, ,q '¡d
?r4xirth r{tlrl d}:'!, I l¡.r!i\) ,J
rrl !¡¡¡j lÀt rù o,A\1kts. [*r ¡r!#.r\ !?r414 r l. r. ¡r1 rh .4J r-f , rn¡t ilÉii,ç. "n¡l _,fl ê
t¿ùû¡& &F¡e d¡dxs, ¡Àt nì¡cq.tri 9r' ! trr¿il¡ft!-F{l)rh{,.qrì' tcd þ6rr ¡
'.,írdn¡,È¡rir ôr¡aþ*J¡t,1.È- /- j*.r'. ¡:+
d ¡¡bÀiI t! ilra¡ fr{:!.il!
6 Sds*rsl0d.t¡iÂsdhrff!¡&Fnhtt!&.(â ¡d b. nriw..rLrlaC.r pL, , " rJ * {.
rqÞü( ¡ ûr:rr "' ; s,i " :iih 'ü r¡' tá h,t 'úlll ¡ Sri r a\*r* r(it
tu . 5ô.ern¡ù drFÙb lln¡lFr* id t¡t! abird{úrt-' ú-.d, W,.- t, s'i 4'.1<l:\F *: Jri\q.h{¡,.i'ú'd. rr\." d ,lL. +' f,irl ú ",.. 1:
^ lu@S¡1Mr¡r4.r'o.r:il¡q tÊûe!,eril.rr,¡i,rrr'J. ^b¡r'r¡d1¡1,r,,!..t-,.rL. h .rk i.' L,.d (,U,. ñ.ilr. $í{r;..iJ ru:.Ì. \lrr 5';..t,;s..sù.rJ 6.Ä:åt c{!d¡< t e!4(5 krha;fr¡!
lX S(,&r Nùnìrh(!
$ (¡rk rdx. ¡ñ'ri'( 1rrÞ ditrrô ftirrú.oÈ.rill..rr!ve¡4#iþrÞ ¡É¡,.F kûsr ¡!bÌñ L¿rã\tlri ra ¡..ir !l¡ ÌdÍ.dYi: id6 d,!ñ
ô r!ô {ht-* d ïrnt<.fr.'Ì-.¡, ' *ast rH! {\',r!rrrrr,\-:k.4ìr4,th,r:iil,.rL:hr.r,i :.ilqr¡-{$ .ùL'.. n¡¡r¡ \ (rr, cÀi!-., \1 rlh ,.,. !,
ü Jft 1 À ¡( !.r- tr ". , ,h¡;..¿ xr¡, * , ,.rì.húht -À¡ú r{rr ar $"¡ì¡i i¡rn¡i r:rg!:.l rf¡¡È¡:t.,.À,,¡rr f. i*; :'t_ $.¡....,¡.¡!.!iì
tl¡wr reb,ú rl,ñe rl ft¿srhddr tr..J..ï.!ù4!r ú!. ø -.,-. r,r,¡.,"i,'.., . *r"', -! Dl; ¿ n'. r¡! r. ¡r .. k!¡ .+ С.i!: .r¡r¡.._ ir.1r",:...,nI I a-t ir. ì
l¡d' l.dn tûñr@r ñlSú{. t.rþdhó@ ìr!:i':1:, ! rlr R. { N.- r.. ir, d , r: ,.r Ftr/r
ry
l Prorocl S¡te
t7-7-728 H-P + KUMAR.Proposed Mountain Shadows Place Minor Subdivision, Mountain
Shadow Drive, Garfield County - Regional Geology Map
Fig.8
Explanation:EagleCollapseGenter(960 sq. mi.)Shallovr ÊvâÞoíitB il- Eågle\iall€y cornìåii$r ðrú EagleVallsv Êvanrlrileìirl'Í litÈlf i'r.rtJ¡diiiVâ¡l-ì{j,:,( I I ,'al, ,. , -*"',:Ì rlt-r/)3:::salfÁlqtþÞf5;grÞCarbondaCollapseCenter(4G0 sq. mi.)rill0 MiirsFeb'r$âry 20'i ?ReÍe¡eûces:Twsto and OtheE l19ZBl(irkhanr xnd Scoil rZCoAi!...1:1.B.l¡Jqori6¡.,,tit,iiJrf,r.I-JI-¡ì.¡6:EI-o/11^ñooÊ.?otre.rAÞo.lr'O<tÞ-'ó7ôYFu)OEoadı's:'<otÞôoE4lqq\o
lntemountain
Selsmic Beh Wyoming Øc
ã
Basin
150 m¡læ
tA/WY NB
U co.
Rocky
Axial Basin Wålden
ELilv Parh
1ti7 1
VI
Sorinos0-o
oç-
rr<tg^
Kregmtrng á
o
o Greeley
N,Forl Morgan
'l.8a2
M 6.2
vil
Mtn
to
Rang€lyB (t)
oc5o
a
Boulder
Vl toVll
M 3.2 to
Meeksr Great*
Rro Blånæ
(Explos¡on)
1973
M 5.7
EEagle
Project
Site
Våil
B Denvsr
EEEF.ism
Rulsu,, ìÊ
^ (Explosion)v t969
Rrfle 2zColoracl
ct^nb^ Grand
2¿
È.o
Plateau
E
Ce6tlð
Rock
0Krowe Limon
M 5.3
Junct¡m
o
S. Grand n
Aspen
toa
2z
Sp
D€ltå U
Moãb f¡o56b
o
Salida
o
S oez)o-o
aP4,i Monlrose1
CrmarronR¡doe Gunnrson1s60 ' nM5s Plains
o20 PueblooE o80
o
Rdgeway
1913
vt è
U)
Q69a
Crty
Walsêoburg
0
O69c
tr
Cortez
E
Alamosa Tflnidad
E 0 Q69d
201
M5vI
1
3
UÏ co Durêngo
E nr¡nrdad
a
AZ Nf\/t Dulæ
1966 Chama E R"ton
M51vlt
Explanation:
- Post-Glacial Faults:
\ Fault yorrngãl. than about 1s.000 years.
Historic Selsmlc Zonesl
Areas with histor¡cally high seismic activlty
Larger Historic Earthquakes:
Ëarlhquakes with maximum intensity greater lhan Vl
or magnilude greater than M 5.0 from 1867 to
present.
M Local, surface wâve or body wave magnitudeVl Modified Mercalli intensity
0 50 ml.* Nuclear Exolosion:
Large underground nuclear exploslon for nalural gas
¡eservolr enhancement.
References:
Widmann and Others (1998)
U. S. Geological Suruey Earlhquaku Catalogs
lrt
Scale: 1 in. = 50 mi.
17-7-728 H-PryKU]vIAR Proposed Mountain Shadow Minor Subdivision
Geologically Young Faults and Larger Historic Earthquakes Fig. 10
H.P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No.17-7-728SOILTYPESilty Sand and GravelSilty Sand and GravelSandy Silty and ClayVery Silty Sand and GravelSilty Sand with GravelSandy SiltSandy SiltSilty Sand and GravelSilty Sand and GravelSilty Sand with GravelUNCONFINEOCOMPRESSIVESTRENGTH(PSRATTERBËRG LII'IÎSPLASTICINDEX(o/"1LIQUIDLIMITlo/"1PERCENTPASSINGNO.200SIEVE3332725lII37J136SAND{o/ol3228GRAVEL(/"1364tNATURALDRYDENSITYlocflt2297116tt7104109111113116NATURALMOISTURECONTENT(%l4.43.25.55.65I6_88.03.22.33.6SAMPLE LOCATIONDEPTH{frt510205I020302V21525BORINGI2aJ