HomeMy WebLinkAboutSoils Report 07.18.2020AMERICAN
GEOSERVICES
Geotechnical Evaluation Report
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Date: Ju 1 20 Project No: 031 - 20
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988 276-4027
July 18, 2020
PROJECT NO: 0314-WS20
CLIENT: Mr. Patrick Shaffer
Reference: Geotechnical Evaluation Report, 198 Midland Point, Carbondale, CO 81623
Dear Mr. Patrick Shaffer,
At your request, we have completed the geotechnical evaluation for the referenced project in
accordance with the American GeoServices, LLC (AGS) Proposal. Results of our evaluation and
design recommendations are summarized below
PROJECT INFORMATION
The site is located as shown in Figure 1 and Figure 2. The proposed development will consist of
residential construction. We do not anticipate significant site grading for this project. We anticipate
proposed structure will be constructed with light to moderate foundation loads.
SCOPE OF WORK
Our scope of services included the geologic literature review, soil explorations, geologic hazards
evaluation, geotechnical evaluation, and the preparation of this report. Evaluation of any kind of
existing structures on and adjacent to the site was beyond our scope of services.
In July 2020, we performed three soil explorations (B1 through B3) at approximate locations
shown in Figure 2 and collected soil/rock samples Our soil exploration included logging of soils
from soil boring. Our explorations extended to a maximum depth of 8 feet below existing ground
surface (BGS)- All soil/rock samples were identified in the field and were placed in sealed
containers and transported to the laboratory for further testing and classification- Logs of all soil
explorations showing details of subsurface soil conditions encountered at the site are included in
1338 Grand Avenue #306
Glenwood Springs, CO 81601
Ph: (303) 325 3869
www.americangeoservices com
sma@amencangeoservices.com
Ph: (888) 276 4027
Fx: (877) 471 0369
Mailing: 191 University Blvd, #375
Denver, CO 80206
Ph: (303) 325 3869
an appendix. The Legend and Notes necessary to interpret our Exploration Logs are also included
in an appendix. Data obtained from site observations, subsurface exploration, laboratory
evaluation, and previous experience in the area was used to perform engineering analyses.
Results of engineering analyses were then used to reach conclusions and recommendations
presented in this report
SURFACE CONDITIONS
The site is roughly a rectangularly -shaped parcel of land as shown in Figure 2_ Currently the site
topography is gently sloping downwards to the east. At the time of our site visit, there was no
visual indication of active slope instability or active landslides in the site vicinity Our review of
available geology maps and geologic hazards information did not reveal the presence of active
geologic hazards at or immediately adjacent to the site.
SUBSURFACE CONDITIONS
Subsurface conditions encountered in our explorations and noted in our literature research are
described in detail in the Exploration Logs provided in an Appendix and in the following
paragraphs. Soil classification and identification is based on commonly accepted methods
employed in the practice of geotechnical engineering. In some cases, the stratigraphic boundaries
shown on Exploration Logs represent transitions between soil types rather than distinct lithological
boundaries. It should be recognized that subsurface conditions often vary both with depth and
laterally between individual exploration locations. The following is a summary of the subsurface
conditions encountered at the site.
Sand -Silt -Clay Alluvium: Site is primarily underlain by generally loose or medium stiff to stiff
mixtures of sand -silt -clay (SM, SC) extending to a depth of about 1.5 feet. These soils exhibited
low plasticity in the field and in the laboratory These soils do not represent old debris flow deposit
or ancient landslide deposit.
Gravel -Sand -Silt Alluvium: Below about 1 5 feet, the site is generally underlain by dense
gravelly alluvium (GM) extending to a maximum exploration depth of 8 feet.
Groundwater: Groundwater was not encountered during exploration or at the time of completion
of our soil explorations This observation may not be indicative of other times or at locations other
than the site Some variations in the groundwater level may be experienced in the future. The
magnitude of the variation will largely depend upon the duration and intensity of precipitation,
temperature and the surface and subsurface drainage characteristics of the surrounding area.
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GEOLOGIC HAZARDS EVALUATION
Expansive/Collapsible Soils: The site is not underlain by highly expansive clayey soils or clayey
sedimentary bedrock materials The site location is not near known swell hazard zones that pose
a significant geotechnical concem. However, local pockets of 'collapsible' soils/materials can
occur through the site and may cause settlement in the foundations or flatwork around the site.
This is typical of many areas along the Roaming Fork River corridor.
Flooding: Proposed construction area is not located within 100-year flood hazard zone, however,
a flood hazard evaluation was beyond our scope of services. We recommend hiring an
experienced hydrologist to evaluate the flood hazards for the site, or an in-depth evaluation of
published flood hazard maps, considering the proximity of the site to the river.
Debris Flow: Site is not located within alluvial fans or flood channels. Debris flow hazard at the
site is minimal under normal site, topographic, geologic, and weather conditions. However, the
site vicinity area may consist of ancient debris flow or ancient landslide deposit, which is currently
inactive.
Rockfall: Site is not located within rockfall hazard zone. Rockfall hazard at the site is minimal
under normal site, topographic, geologic, and weather conditions.
Landslides: Our review of available geologic maps and landslide hazard maps did not indicate
that recent landslides or recent debris flow had occurred at the site or in the immediate proposed
building area During our site reconnaissance, we did not notice scarps, crevices, depressions,
tension cracks in the ground surface, irregular slope toes, exposed surfaces of ruptures without
vegetation, presence of distinct fast-growing vegetation, undrained depressions, etc , that are
generally indicative of local active and/or inactive landslides or slope instability that would
adversely impact the on -site structure at this time, however, a detailed landslide evaluation of any
kind or slope stability evaluation under seismic conditions was beyond our scope of services
The site is not located within the mapped landslide hazard areas surrounding the site (Figure 6)
There are potentially mapped landslides and/or ancient landslide deposits close to the site
boundaries, within 750-1000 feet to the west. There is also moderate to high potential for the
presence of dormant and/or unknown historic landslides, deep-seated ancient landslides, or
geologically -recently developed dormant landslides in the site vicinity close to the site, but not at
the site.
The site itself is not mapped as being situated within the existing active or ancient active landslide
mass or an ancient active global landslide. However, the site vicinity area to the west is mapped
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as having landslide hazard (Figure 6) Considering these findings, the site topography, and site
geologic conditions, it is our opinion that the immediate site vicinity area (but not the site) have
'site -specific landslide hazards' and has some 'inherent' risk associated with slope instability and
structural impact from the movement of any globat/ancient landslide and local slope movements.
Moreover, historically, with construction in such areas, there is always an inherent risk associated
with ground movement and/or settlements and related structural damage. The owner should
understand these inherent risks related to site vicinity. If the owner wants to better understand the
risks and to eliminate the site -specific landslide hazard risks, then a detailed and comprehensive
geotechnical evaluation including deep drilling, detailed slope stability modeling, and a detailed
geologic hazards assessment (including global landslide hazards evaluation) should be
performed in the site vicinity area to quantify the abovementioned risks and to provide detailed
geotechnical design recommendations for comprehensive mitigation measures. Unless these
recommended studies are performed, the owner is completely responsible for taking all risks
associated with any future potential for instability at the site occurring due to landslide hazards in
the site vicinity.
Initial Slope Stability Evaluation: Based on the results of our initial analyses (as discussed in
following paragraphs), in our opinion, at present there are no slope instability hazards at the site
provided site drainage is properly maintained during the design fife of the structure.
Using the results of geologic and soils literature review (as attached in the appendix) and site
reconnaissance data, we analyzed on -site slopes by performing preliminary slope stability
analysis. We used the software SLOPEIW to model on -site slopes, subsurface soil conditions,
and the impact of existing construction on the stability of the site. We used several methods
(Bishop, Janbu, Spencer, etc.) in order to obtain the lowest factor of safety against slope failures
The SLOPENV computer software calculates the most likely failure plane based on topography,
subsurface conditions (including soil parameters), and groundwater conditions. The stability of
this most likely failure plane is calculated as the factor of safety (FOS), which is a ratio of the
resisting forces or shear strength to the driving forces or shear stress required for equilibrium of
the slope A FOS of 1.0 indicates the resistive forces and driving forces are equal. A FOS below
1.0 indicates the driving forces are greater and the landslide is active. A FOS above 1 0 indicates
the resisting forces are greater and the slope is stable Based on the engineering community and
our experience, a factor of safety in the range of 1.3-2.0 is generally acceptable to assure slope
stability in residential applications.
Slope stability analysis was performed using various input soil parameters derived from the results
of our subsurface exploration and laboratory evaluation, in order to properly evaluate the stability
of a slope Of particular importance were surface and subsurface profiles (slope geometry), soil
strength parameters, and groundwater conditions. Based on our experience with past slope
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stability evaluations in similar geologic conditions, soil strength parameters can vary considerably
Notwithstanding, we used soil strength values typical of on -site soils and native soils/bedrock
based on our experience with soil strength testing, as well as back -calculation of soil strength
parameters for failed slopes in similar geologic conditions
For our "design" slope stability analysis, which was used as a basis for obtaining our
recommended geotechnical parameters for initial site design, we assigned optimal range of soil
parameters. We assumed the presence of perched groundwater and soil saturation in order to
model possible broken drainage pipes in future. During slope stability analyses, both translational
and circular failure surfaces were considered. A sensitivity analysis was also performed using
various soil strength values, groundwater configurations and slip surface profiles. We analyzed
a typical cross section using post -construction conditions in order to determine the FOS of the
slope Based on the results of our initial analyses (as discussed in following paragraphs), in our
opinion, at present there are no slope instability hazards at the site provided site drainage is
properly maintained during the design fife of the structure.
Based on the results of our slope stability analyses, we recommend a building setback of at least
80 feet from the edge of the riverbanks.
Inherent Slope Instability Risks: Historically, with construction in areas adjacent to riverbanks,
there is an inherent risk associated with slope failures along the riverbanks. Although there was
no active slope instability observed within the proposed building envelope or adjacent to the river
banks, and the potential for future active slope failure is low, the owner is still responsible for
taking any risks associated with any existing or future potential for instability at the site or in the
river bank areas Since this report and recommendations continued herein have been prepared
in order to maintain a low degree of risk for future slope instability, all of our recommendations
should be strictly followed.
Earthquakes: Based on site geology, topography, and our preliminary evaluation, in our opinion,
the site is generally not considered to be located within highly active seismic area. Therefore,
anticipated ground motions in the region due to seismic activity are relatively low and do not pose
a significant hazard Ground accelerations in excess of 0.1 g to -0.2g are not anticipated to occur
at the site.
Based on the results of our subsurface explorations and review of available literature (2009
International Building Code), in our opinion, a site classification "C" may be used for this project
However, this site classification may be revised by performing a site -specific shear wave velocity
study.
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Subsurface soil conditions at the site are not susceptible to liquefaction Seismically induced slope
instability may occur on a global scale impacting not just the site but also the surrounding area,
however, such an evaluation was beyond our scope of services A detailed seismic hazards
evaluation of the site was beyond our scope of services.
CONCLUSIONS AND RECOMMENDATIONS
Based on the results of our geotechnical evaluation, in our opinion, the site is suitable for the
proposed construction provided following recommendations are strictly followed. It should be
noted that our conclusions and recommendations are intended as design guidance. They are
based on our interpretation of the geotechnical data obtained during our evaluation and following
assumptions:
Proposed/Final site grades will not differ significantly from the current site grades;
• Proposed foundations will be constructed on level ground; and
• Structural loads will be static in nature.
Construction recommendations are provided to highlight aspects of construction that could affect
the design of the project. Entities requiring information on various aspects of construction must
make their own interpretation of the subsurface conditions to determine construction methods,
cost, equipment, and work schedule.
SHALLOW FOUNDATIONS
We recommend that the proposed structure be supported on shallow spread footings designed
and constructed in accordance with following criteria:
Due to the presence of potential non -uniform soil conditions, over -excavate the soils from
within the foundation areas to a depth of 12 inches below the bottom of footings, then surficial
compact the excavated surface and call AGS for an open hole inspection.
Backfill with granular free -draining structural fill (or onsite sandy soils) compacted to at least
95% of ASTM D698 maximum dry density in order to achieve a "uniform subgrade" and 10
facilitate the placement of foundation drain. Over -excavation can also be minimized or
eliminated based on the results of open -hole inspection or foundation subgrade inspection
performed by AGS. Onsite materials may be used as structural fill, provided they are
approved by AGS.
• Foundations bearing upon properly prepared and approved subgrade should be designed for
a maximum allowable bearing pressure of 2,000 pounds per square foot (psf).
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Estimated final structural loads will dictate the final form and size of foundations to be
constructed However, as a minimum, we recommend bearing walls be supported by
continuous footings of at least 18 inches in width. Isolated columns should be supported on
pads with minimum dimensions of 24 inches square.
Exterior footings and footings in unheated areas should extend below design/preferred frost
depth of 36 inches.
Continuous foundation walls should be reinforced in the top and bottom to span an
unsupported length of at least 8 feet to further aid in resisting differential movement. As a
minimum, additional reinforcement as shown in Figure 7 should be placed.
• Foundation/stem walls should be adequately designed as retaining walls and adequate
drainage measures should be implemented as shown in Figure 8.
We estimate total settlement for foundations designed and constructed as discussed in this
section will be one inch or less, with differential settlements on the order of one-half to three -
fourths of the total settlement
OPTIONAL: DRILLED PIERS or DEEP FOUNDATIONS
This option can be used if the owner wants to significantly reduce the risk of future differential
settlements and related structural damage to a level of minimal to none, and to significantly
increase the safety factors for foundation stability Following recommendations are provided to
highlight aspects of design and construction that could significantly affect the performance of the
project. Entities requiring information on various aspects of design must make their own
interpretation of the subsurface conditions. After the review of structural and architectural project
plans and proposed loads and grading, we may recommend deeper soil borings to confirm or to
modify following recommendations:
• Piers should have a minimum design length of 10 feet below the bottom of foundation level.
• The minimum pier diameter (D) will depend on the length (L) to diameter ratio (UD). We
recommend the UD not exceed 30.
•
•
A minimum pier diameter of 12 inches is recommended to facilitate proper cleaning and
observation of the pier hole during construction. This recommendation can be modified after
the discussions with your foundation contractor and/or structural engineer.
Piers should be designed for an allowable end bearing capacity of 10,000 psf and an allowable
skin friction value of 1,500 psf for the minimum 5 feet embedded portion of the pier into the
medium dense to dense material present below a depth of 5 feet. Where there will be tension
loads or uplift on the piers, the tension loads should be resisted by skin friction of the pier
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embedded below 10 feet of existing ground surface. The skin friction value of 1,250 psf can
be used to calculate uplift capacity.
Some movement of drilled pier foundations should be anticipated to mobilize skin friction. We
estimate the required movement will be on the order of 1/8 to 1/4 inch. Differential movement
between adjacent piers may equal the total movement.
All axially loaded piers should have a minimum center -to -center spacing of at least three pier
diameters (3D) All laterally loaded piers should have a minimum center -to -center spacing of
at least six pier diameters (6D) in the direction parallel to pier loading, and 2.5 diameters
(2 5D) in the direction perpendicular to pier loading. Piers placed closer than these values
should be designed using the appropriate reduction factors to account for group action. For
the final design, the exact geometry of the pier group should be submitted to us for review and
approval so that appropriate modifications can be made to our recommendations.
• Piers should be adequately reinforced to their full length. Reinforcement should extend well
into grade beams and walls Steel to pier ratio of a minimum of 0 005 based on cross -sectional
area of pier is recommended. More reinforcement may be required from structural
considerations As a minimum, one #5 rebar per 18-inch pier diameter should be used to resist
uplift tension generated by swelling soils.
The project specifications should allow for modifications by geotechnical engineer during the
pier installation
The contractor should mobilize proper equipment so that drilling in gravels/river rock or
unanticipated hard materials can be achieved to required depths. The contractor should
carefully review this report to account for all possibilities and extras in their bid to avoid high
cost overruns.
• The use of casing and dewatering equipment is anticipated. However, it is contractor's
responsibility to make the determination regarding the use of casing and dewatering
equipment.
• Mushrooming of the pier top should be avoided by not allowing the pier size to vary towards
the ground surface
Drilled pier holes should be cleaned of loose material prior to concrete placement. Once the
proper depth is achieved, the auger should be placed in the bottom of the hole and several
high-speed revolutions should be made to clean the bottom. Loose cuttings should not remain
in the bottom of the excavations prior to concrete placement.
Concrete should be onsite and ready during drilling of piers. Concrete should be placed
immediately after pier observations and measurements are made, and reinforcement is set
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•
•
within the hole. Groundwater was encountered during our investigation and is anticipated to
be a significant factor during construction of the piers. Pier holes should not be left 'open"
ovemight.
Concrete to be placed in the piers should have a slump of 4 to 7 inches. If more than 3 inches
of water is present in the bottom of the pier hole, de -watering should be performed using a
pump or tremie prior to concrete placement.
Installation of drilled piers should be observed by a member of American GeoServices, LLC
on a full-time basis to identify and confirm that subsurface conditions are consistent with those
encountered in our soil borings, and to monitor construction procedures.
Assuming that the pier length to diameter ratio (L/D) will be greater than 7, in our opinion, the
Matlock and Reese method of analysis can be used for lateral load analyses. Therefore, the
lateral soil -structure interaction of single shafts may be analyzed using the software
application, LPILE developed by Ensoft, Inc (or equivalent such as COM624) This analysis
procedure estimates the lateral load -displacement behavior based on elastic beam -column
theory and soil reaction -displacement (p-y) curves. Deflection, bending moment and shear
profiles at specified intervals along the length of the shaft are computed.
For lateral load analysis, modulus of horizontal subgrade reaction values of 20 tcf and 35 tcf
may be used for the overburden soils present in upper 10 feet and denser materials present
below 10 feet, respectively. Resistance to lateral load in upper 5 feet should be neglected
As noted earlier, all laterally loaded piers should have a minimum center -to -center spacing of
at least six pier diameters (6D) in the direction parallel to pier loading, and 2.5 diameters
(2 5D) in the direction perpendicular to pier loading. Piers placed closer than these values
should be designed using the appropriate reduction factors to account for group action For
the final design, the exact geometry of the pier group should be submitted to us for review and
approval so that appropriate modifications can be made to our recommendations. Total lateral
load versus deflection graph for the pier group can be developed by adding the lateral load
resistance of piers at selected deflections.
For a detailed LPILE analysis, we should be contacted to provide specific input soil
parameters or to review input parameters and to participate in the pile design along with
project structural engineers.
STRUCTURAL FLOOR & CRAWL SPACE
We understand a structural/framed floor with crawl space may be used for this project. The grade
beams (if used) and floor system should be physically isolated from the underlying soil materials
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with crawl -space type construction. The void or crawl space of minimum of 6 inches or whatever
minimum current Uniform Building Code (UBC) requirement is
For crawl -space construction, various items should be considered in the design and construction
that are beyond the scope of geotechnical scope of work for this project and require specialized
expertise. Some of these include design considerations associated with clearance, ventilation,
insulation, standard construction practice, and local building codes. If not properly drained and
constructed, there is the potential for moisture to develop in crawl -spaces through transpiration of
the moisture/groundwater within native soils underlying the structure, water intrusion from
snowmelt and precipitation, and surface runoff or infiltration of water through irrigation of lawns
and landscaping. In crawl space, excessive moisture or sustained elevated humidity can increase
the potential for mold to develop on organic building materials. A qualified professional engineer
in building systems should address moisture and humidity issues.
CRAWL SPACE PERIMETER/UNDERDRAIN SYSTEM
In order for the crawl space to remain free of moisture, it is important that drainage
recommendations are properly implemented, and adequate inspections are performed prior to the
placement of concrete.
As a minimum, subgrade beneath a structural floor system should be graded so that water
does not pond Perimeter drains and under -slab drains should be installed in conjunction with
a sump pump system to eliminate the potential for ponding and any subsequent damage to
foundation and slab elements. The lot -specific perimeter dewatering, and underdrain systems
should be properly designed and connected to the area underdrain system or a sump -pump
system for suitable discharge from the lot.
Drainage recommendations illustrated in Figure 8 should be implemented. The subsurface
drainage system should consist typically of 4-inch minimum diameter perforated rigid PVC or
flexible pipe (rigid preferred due to depth of placement) surrounded by at least one pipe
diameter of free draining gravel. The pipe should be wrapped in a geosynthetic to prevent fine
soils from clogging the system in the future. The pipe should drain by gravity to a suitable all-
weather outlet or a sump -pit. Surface cleanouts of the perimeter drain should be installed at
minimum serviceability distances around the structure. A properly constructed drain system
can result in a reduction of moisture infiltration of the subsurface soils. Drains which are
improperly installed can introduce settlement or heave of the subsurface soils and could result
in improper surface grading only compounding the potential issues.
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The underdrain system should consist of adequate lateral drains and a main drain, regular
clean out and inspection locations, and proper connections to the sump -pump system for
discharge into suitable receptacles located away from the site
• The entire design and construction team should evaluate, within their respective field of
expertise, the current and potential sources of water throughout the life of the structure and
provide any design/construction criteria to alleviate the potential for moisture changes. If
recommended drain systems are used, the actual design/layout, outlets, locations, and
construction means, and methods should be observed by a representative of AGS
SLAB -ON -GRADE AND PERIMETER/UNDERDRAIN SYSTEM
Groundwater is not expected to be at depths below the proposed foundation levels if excavation
is performed during dry seasons. In order to assure proper slab -on -grade construction (if used),
following recommendations should be strictly followed:
• A perimeter dewatering system should be installed to reduce the potential for groundwater
entering slab -on -grade areas. The lot -specific perimeter dewatering should be properly
designed and connected to the area underdrain system or a sump -pump system for suitable
discharge from the lot,
• As a minimum, drainage recommendations illustrated in Figure 8 should be implemented The
subsurface drainage system should consist typically of 4-inch minimum diameter perforated
rigid PVC or flexible pipe (rigid preferred due to depth of placement) surrounded by at least
one pipe diameter of free draining gravel The pipe should be wrapped in a geosynthetic to
prevent fine soils from clogging the system in the future. The pipe should drain by gravity to
a suitable all-weather outlet or a sump -pit. Surface cleanouts of the perimeter drain should
be installed at minimum serviceability distances around the structure. A properly constructed
drain system can result in a reduction of moisture infiltration of the subsurface soils Drains
which are improperly installed can introduce settlement or heave of the subsurface soils and
could result in improper surface grading only compounding the potential issues
• The entire design and construction team should evaluate, within their respective field of
expertise, the current and potential sources of water throughout the life of the structure and
provide any design/construction criteria to alleviate the potential for moisture changes. If
recommended drain systems are used, the actual design/layout, outlets, locations, and
construction means, and methods should be observed by a representative of AGS.
The "Slab Performance Risk" associated with native soils is "Low". Therefore, the slab can be
constructed as a slab -on -grade provided the owner is aware that there is still potential risk of
some slab movement due to presence of possibly collapsible soils. Proper wetting of the
subgrade to obtain soil moisture content in the range of 20-22% and/or moisture -conditioning and
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recompaction of onsite materials for upper 2 feet should reduce the risk of movement If the
owner is not willing to assume any risk, then a structural floor slab system option should be
considered.
The actual slab movements that will occur on a particular project site are very difficult, if not
impossible, to predict accurately because these movements depend on loads, evapo-
transpiration cycles, surface and subsurface drainage, consolidation characteristics, swell index,
swell pressures and soil suction values. The actual time of year during which the slab -on -grade
is constructed has been found to have a large influence on future slab -on -grade movements.
Slab heaves or settlements are normally defined in terms of "total" and "differential" movement.
"Total" movement refers to the maximum amount of heave or settlement that the slab may
experience as a whole. "Differential' movement refers to unequal heave or settlement that
different points of the same slab may experience, sometimes over relatively short horizontal
distances Differential movements are arbitrarily determined to be one-half of the total movement
in soils exhibiting Low Slab Performance Risk. Greater differential movements can occur in areas
where expansive soils have been encountered and where the natural soils abruptly transition to
fill material.
For design of floor slabs, a modulus of subgrade reaction of 200 pounds per cubic inch (pci) may
be used Based on the results of our analyses, we believe that interior floor slabs designed as
recommended above and constructed as recommended in following paragraphs could result in
"total" movement of approximately up to 1-inch with "differential" movement on the order of half
the total movement.
We recommend that the construction measures outlined in the following paragraphs be followed
to reduce potential damage to floor slabs, should excessive wetting of the subsurface soils occur:
• Design and construct the floor slab to move independently of bearing members (floating slab
construction) Provide slip joints around exterior walls and interior columns to allow free
vertical movement of the slabs.
Frequent control joints should be provided at about 10 feet spacing in the floor slab to reduce
problems with shrinkage and cracking according to ACI specifications. Control joint spacing
is a function of slab thickness, aggregate size, slump and curing conditions. The requirements
for concrete slab thickness, joint spacing, and reinforcement should be established by the
designer, based on experience, recognized design guidelines and the intended slab use
Placement and curing conditions will have a strong impact on the final concrete slab integrity
Floor slabs should be adequately reinforced with welded wire mesh and steel rebar. Structural
engineer should include steel rebar in addition to welded wire mesh in order to reduce the risk
of differential movement due to bending over 8 feet of unsupported length
The need for a vapor ban-ier will depend on the sensitivity of floor coverings to moisture If
moisture sensitive floor coverings are proposed for portions of the proposed structure, a
capillary break material, typically consisting of a "clean" gravel, should be considered. We can
provide additional recommendations if this is the case.
• Provided gravel is desired below the slab, a layer of 4 to 6 inches can be used. Plumbing
passing through slabs should be isolated from the slabs and provided with flexible connections
to allow for movement. Under slab plumbing should be avoided if possible and should be
brought above the slab as soon as possible.
• If slab -bearing partitions are used, they should be designed and constructed to allow for
movement A minimum of 2 inches of void space (as illustrated in Figure 3) should be
maintained below or above partitions. If the void is provided at the top of partitions, the
connections between the interior, slab -supported partitions and exterior foundation supported
walls should allow for differential movement.
Where mechanical equipment and HVAC equipment are supported on slabs, we recommend
provision of a flexible connection between the fumace and ductwork with a minimum of 2
inches of vertical movement
RETAINING WALL
Retaining walls for at -rest conditions can be designed to resist an equivalent fluid density of 55
pcf for on -site fill materials if needed only imported granular ball meeting CDOT Class 1
structural backfill should be used Retaining walls for unrestrained conditions (free lateral
movement) can be designed to resist an equivalent fluid density of 35 pcf for on -site fill materials
and 35 pcf for imported granular backfill or CDOT Class 1 structural backfill. For passive
resistance of unrestrained walls, we recommend passive resistance of 300 psf per foot of wall
height A coefficient of friction value of 0 35 may be used for contact between the prepared soil
surface and concrete base.
The above recommended values do not include a factor of safety or allowances for surcharge
loads such as adjacent foundations, sloping backfill, vehicle traffic, or hydrostatic pressure. We
should be contacted to provide additional recommendations for any specific site retaining
conditions
Retaining wall backfill should be placed in strict accordance with our earthwork recommendations
given below and as illustrated in Figure 8. Backfll should not be over -compacted in order to
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minimize excessive lateral pressures on the walls. As a precautionary measure, a drainage
collection system (drains or geosynthetic drains) should be included in the wall design in order to
minimize hydrostatic pressures. A prefabricated drainage composite or drain board such as the
MiraDrain 2000 or an engineer -approved equivalent may be installed along the backfilled side of
the basement foundation wall.
EARTHWORK CONSTRUCTION
Site grading should be carefully planned so that positive drainage away from all structures is
achieved. Following earthwork recommendations should be followed for all aspects of the project
Fill material should be placed in uniform horizontal layers (lifts) not exceeding 8 inches before
compacting to the required density and before successive layers are placed. If the contractor's
equipment is not capable of properly moisture conditioning and compacting 8-inch lifts, then the
lift thickness shall be reduced until satisfactory results are achieved.
Clays or weathered sandstone/claystone bedrock (if encountered) should not be re -used onsite
except in landscaped areas. Import soils should be approved by AGS prior to placement. Fill
placement observations and fill compaction tests should be performed by AGS Engineering in
order to minimize the potential for future problems. Fill material should not be placed on frozen
ground. Vegetation, roots, topsoil, the existing fill materials, and other deleterious material to
depth of approximately 6 inches should be removed before new fill material is placed
On -site fill to be placed should be moisture treated to within 2 percent of optimum moisture content
(OMC) for sand fill and from OMC to 3-4 percent above OMC for clay and weathered bedrock.
Fill to be placed in wall backfill areas and driveway areas and all other structural areas should be
compacted to 95% of Standard Proctor (ASTM D 698) dry density or greater. Compaction in
landscape areas should be 85% or greater.
Imported structural fill should consist of sand or gravel material with a maximum particle size of 3
inches or less. In addition, this material shall have a liquid lirnit less than 30 and a plasticity index
of 15 or less. Structural fill should also have a percent fine between 15 to 30 percent passing the
No 200 sieve. Structural fill should be moisture conditioned to within 2 percent of OMC and
compacted to at least 95 percent of Standard Proctor (ASTM D698) dry density
In our opinion, the materials encountered at this site may be excavated with conventional
mechanical excavating equipment. For deeper excavations, heavier equipment with toothed
bucket may be required. Although our soil explorations did not reveal "buried" foundation elements
Project Na 0314-WS20
July 18, 2020
Page No: 14 of 18
or other structures or debris within the building footprint, these materials may be encountered
during excavation activities Debris materials such as brick, wood, concrete, and abandoned
utility lines, if encountered, should be removed from structural areas when encountered in
excavations and either wasted from the site or placed in landscaped areas
Temporary excavations should comply with OSHA and other applicable federal, state, and local
safety regulations In our opinion, OSHA Type B soils should be encountered at this site during
excavation. OSHA recommends maximum allowable unbraced temporary excavation slopes of
1.25:1(H:V) for Type B soils for excavations up to 10 feet deep. Permanent cut and fill slopes are
anticipated to be stable at slope ratios as steep as 2H:1V (horizontal to vertical) under dry
conditions. New slopes should be revegetated as soon as possible after completion to minimize
erosion.
We recommend a minimum of 12 feet of clearance between the top of excavation slopes and soil
stockpiles or heavy equipment or adjacent structures. This setback recommendation may be
revised by AGS once the project plans are available for review If braced excavations or shoring
systems are to be used or needed, they should be reviewed and designed by AGS. It should be
noted that near -surface soils encountered at the site will be susceptible to some sloughing and
excavations should be periodically monitored by AGS's representative.
The proposed excavation should not adversely impact any existing structures. Proper shoring
and/or underpinning should be used to maintain the stability of existing structure as well as the
excavated faces of the new construction area.
It should be noted that the above excavation recommendations are commonly provided by local
consultants. The evaluation of site safety during construction, stability of excavated slopes and
cuts, and overall stability of the adjacent areas during and after construction is beyond our scope
of services. At your request, we can provide these services at an additional cost.
During construction in wet or cold weather, grade the site such that surface water can drain readily
away from the building areas. Promptly pump out or otherwise remove any water that may
accumulate in excavations or on subgrade surfaces and allow these areas to dry before resuming
construction Berms, ditches and similar means may be used to prevent storm water from
entering the work area and to convey any water off -site efficiently.
If earthwork is performed during the winter months when freezing is a factor, no grading fill,
structural fill or other fill should be placed on frosted or frozen ground, nor should frozen material
be placed as fill. Frozen ground should be allowed to thaw or be completely removed prior to
placement of fill. A good practice is to cover the compacted fill with a "blanket" of loose fill to help
Project Na 0314-WS20
July 18, 2020
Page Na 15 of 18
prevent the compacted fill from freezing ovemight The "blanket" of loose fill should be removed
the next moming prior to resuming fill placement.
During cold weather, foundations, concrete slabs -on -grade, or other concrete elements should
not be constructed on frozen soil. Frozen soil should be completely removed from beneath the
concrete elements, or thawed, scarified and re -compacted The amount oftime passing between
excavation or subgrade preparation and placing concrete should be minimized during freezing
conditions to prevent the prepared soils from freezing. Blankets, soil cover or heating as required
may be utilized to prevent the subgrade from freezing
GENERAL DRAINAGE
Proper drainage is critical for achieving long-term stability and overall success. In general, where
interior floor elevations are situated at an elevation below proposed exterior grades, we
recommend installation of a perimeter drains around the exterior grade beam and foundations as
illustrated in Figure 8. In addition, drain laterals that span the crawl space are recommended to
prevent ponding of water within the crawlspace (if used). If necessary, AGS can provide further
recommendations for the exterior drain system and a typical drain detail.
Groundwater was encountered at depth at the time of our explorations However, based on the
weather and surface water run-off conditions in the site vicinity area during construction, site may
require pumping and other dewatering methods during construction.
Proper surface drainage should be maintained at this site during and after completion of
construction operations The ground surface adjacent to buildings should be sloped to promote
rapid run-off of surface water. We recommend a minimum slope of six inches in the first five
horizontal feet for landscaped or graveled areas. These slopes should be maintained during the
service life of buildings. If necessary, adequate interceptor drains should be installed on uphill
sides to intercept any surface water run-off towards the site.
Landscaping should be limited around building areas to either xeri-scaping, landscaping gravel,
or plants with low moisture requirements No trees should be planted or present within 15 feet of
the foundations. Irrigation should be minimal and limited to maintain plants Roof downspouts
should discharge on splash -blocks or other impervious surfaces and directed away from the
building. Ponding of water should not be allowed immediately adjacent to the building
It is important to follow these recommendations to minimize wetting or drying of the foundation
elements throughout the life of the facility. Construction means and methods should also be
Project No: 0314-WS20
July 18, 2020
Page Na 16 of 18
utilized which minimize improper increases/decreases in the moisture contents of the soils during
construction.
Again, positive drainage away from the new structures is essential to the successful performance
of foundations and flatwork and should be provided during the life of the structure. Paved areas
and landscape areas within 10 feet of structures should slope at a minimum grade of 10H:1V
away from foundations. Downspouts from all roof drains, if any, should cross all backfilled areas
such that they discharge all water away from the backfill zones and structures. Drainage should
be created such that water is diverted away from building sites and away from backfill areas of
adjacent buildings
CONCRETE CONSTRUCTION
Concrete sidewalks and any other exterior concrete flatwork around the proposed structure may
experience some differential movement and cracking. While it is not likely that the exterior
flatworks can be economically protected from distress, we recommend following techniques to
reduce the potential long -tens movement:
Scarify and re -compact at least 12 inches of subgrade material located immediately beneath
structures
Avoid landscape irrigation and moisture holding plants adjacent to structures. No trees should
be planted or present within 15 feet of the foundations.
• Thicken or structurally reinforce the structures
We recommend Type I -II cement for all concrete in contact with the soil on this site. Calcium
chloride should not be added. Concrete should not be placed on frost or frozen soil Concrete
must be protected from low temperatures and properly cured.
LIMITATIONS
Recommendations contained in this report are based on our field observations and subsurface
explorations, limited laboratory evaluation, and our present knowledge of the proposed
construction. It is possible that soil conditions could vary between or beyond the points explored
If soil conditions are encountered during construction that differ from those described herein, we
should be notified so that we can review and make any supplemental recommendations
necessary. If the scope of the proposed construction, including the proposed loads or structural
locations, changes from that described in this report, our recommendations should also be
reviewed and revised by AGS.
Project Na 0314-W820
July 18, 2020
Page Na 17 of18
Our Scope of Work for this project did not include research, testing, or assessment relative to past
or present contamination of the site by any source If such contamination were present, it is very
likely that the exploration and testing conducted for this report would not reveal its existence. If
the Owner is concemed about the potential for such contamination, additional studies should be
undertaken We are available to discuss the scope of such studies with you. No tests were
performed to detect the existence of mold or other environmental hazards as it was beyond Scope
of Work.
Local regulations regarding land or facility use, on and off -site conditions, or other factors may
change over time, and additional work may be required with the passage of time. Based on the
intended use of the report within one year from the date of report preparation, AGS may
recommend additional work and report updates. Non-compliance with any of these requirements
by the client or anyone else will release AGS from any liability resulting from the use of this report
by any unauthorized party. Client agrees to defend, indemnify, and hold harmless AGS from any
claim or liability associated with such unauthorized use or non-compliance.
In this report, we have presented judgments based partly on our understanding of the proposed
construction and partly on the data we have obtained. This report meets professional standards
expected for reports of this type in this area. Our company is not responsible for the conclusions,
opinions or recommendations made by others based on the data we have presented. Refer to
American Society of Foundation Engineers (ASFE) general conditions included in an appendix.
This report has been prepared exclusively for the client, its' engineers and subcontractors for the
purpose of design and construction of the proposed structure. No other engineer, consultant, or
contractor shall be entitled to rely on information, conclusions or recommendations presented in
this document without the prior written approval of AGS.
We appreciate the opportunity to be of service to you on this project. If we can provide additional
assistance or observation and testing services during design and construction phases, please call
us at 1 888 276 4027
Sincerely,
Sam Adettiwar, MS, PE, GE, P.Eng, M.ASCE
Senior Engineer
Attachments
Project No: 0314-WS20
July 18. 2020
Page No: 18 of 18
FIGURES
•
REFERENCE: *T
GOOGLE MAPS l�
USGS TOPOGRAPHIC MAPS
IIILSITE EPCASnON
L
1-617
SITE LOCATION
•
riOT
AMERICAN GI OSL IZVIil S
FIGURE 1: SITE LOCATION MAP
NOTE:
SCHEMATIC PLAN TO SHOW APPROXIMATE SUBSURFACE EXPLORATION LOCATION ONLY; NOT SURVEYED.
LflGEND
4t)
N
DESIGNATES SUBSURFACE EXPLORATION LOCATION, BY AMERICAN GEOSERVICES, LLC. ,JULY 2020 SEE EXPLORATION
LOG IN APPENDIX FOR FURTHER DETAILS
REFERENCE:
GARFIELD COUNTY
COLORADO GIS
AMERICAN GEOSERVICES
FIGURE 2: SCHEMATIC SITE PLAN
\ Oa
J,•
x
x
ly
O4 4'0
Pee ,
Qta
OI0
Qdfy
1 �1,
i.
i -
Qltir
•. OcI y
, • Pee
y CD.5A Gi10
CD{Z
•
SfTE LOCATION
Qa.
x X X QCU
• Oc
Odsy
- Pee
OacoPc
LEGEND
Oly 1 Younger terrace alluvium (late Pleistocene( —Mostly
poorly sorted, etas( -supported, locally boulderv, pebble
and cobble gra.-el in a sand and silt matrix. Deposited
as glacial ouhvnsh Underlie. terrace. 14-1), 11 above
modern stream level. May Delude foe• -grained
erbank deposits
Stream -channel, flood -plain. and low -terrace deposits
(Holocene and late Pleislocenel—Moll Iv poorly.orted,
elaa-snpporled g ,el it and, , .ion maul.
Include. teases tip to ohm it i2 ft atlamodern ricer
lee al
T
REFERENCE:
U S GEOLOGICAL MAPS
.3
ti
h
Qty
r e'tti
ocify
Odfy ,I Younger debris -flow deposits (Holocene and late
Pleistocenel—Poorly sorted to moderately wen-vrrted,
maim- and clasl•,opporled deposits ranging front
elly and
silt to sandy, silty, eobbly, pebbly. and
boulder gran el Fan heads tend to be boulder while
distal fan area, are finer grained. Includes debris -floe,
hvpereoncelr.tcd-flow, via I, and sheebeash
deposits on ad..e fans and in some drainage channels
AM I Rk:AN GLOSLRVICIS
FIGURE 3: GEOLOGIC MAP
REFERENCE:
WEB SOIL SURVEY
LEGEND
Aspen -Gypsum Area, Colorado, Parts of Eagle,
Garfield, and Pitkin Counties (C0655)
Aspen -Gypsum Area, Colorado, Parts of '
Eagle, Garfield, and Pitkin Counties
(C0655)
Map
Unit
Symbol
13
Acres
Map Unit Name in
AOI
Percent
of AOI
Atencio-Azeltine 3.3 31.2%
complex, 3 to 6
percent slopes
39 Evanston loam, 6 3.7 35.5%
to 25 percent
slopes
92 Redrob loam, 1 to 6 3.0 28.3D/o
percent slopes
120 Water
Totals for Area of
Interest
0.5 5.1%
10.6 100.0%
N
1 , A1M1LRICAI.' GEOSLRVICLS
FIGURE 4: SOIL SURVEY MAP
REFERENCE:
COLORADO GEOLOGICAL
SURVEY
SITE LOCAflON
if—
Legend
Collapsable_Soils_withMeeker
EG-14 EoiIan (wind -Hawn) deposits
EG-1A. Dune and sheet sand deposits
PG-14 Cretaceous andTertiary Formations
EG-14 Evaporate Formations
100. AMERK.'.N f:l.t!I IZVICES
FIGURE 5: COLLAPSIBLE SOILS MAP
SITE LOC,ATIQN
REFERENCE:
COLORADO LANDSLIDES
INVENTORY
Colomdo_Iandslide_rnventory_new
Geo,g,,adzlnde.
✓,l
1 tik1ER1. \ \ G[ OSERVICES
FIGURE 6: LANDSLIDES HAZARD
NOTES:
A ADDITIONAL REINFORCEMENT, #4 CONTINUOUS BAR,
BOTTOM OF FOOTING.
B ADDITIONAL REINFORCEMENT, #4 AT 48' C/C, TOP OF
FOOTING.
C. REINFORCEMENT AS PER STRUCTURAL ENGINEERS
DESIGN. AS A MINIMUM, USE #4 AT 48" C/C.
NOTES:
RETAINING WALL DIMENSIONS AND
REINFORCEMENT TO BE DONE BY
PROJECT STRUCTURAL ENGINEER BASED
ON GEOTECHNICAL RECOMMENDATIONS.
CONCRETE FOOTING TO BE
DIMENSIONED BY PROJECT
STRUCTURAL ENGINEER BASED ON
GEOTECHNICAL RECOMMENDATIONS.
ADDITIONAL FOOTING REINFORCEMENT DETAIL
NEW INTERIOR
PART ON WALL
D. 40d NAILS EVERY 24' THROUGH BOTTOM PLATE
INTO PRE -DRILLED HOLES OF THE FLOOR PLATE.
WALL BASE BOARD
NAILED ONLY TO BASE
PLATE; TOP IS FREE
3" MIN VOID SPACE
"FLOAT" (FLOATING WALL DETAIL)
WALL FINISH
MATERIAL
PRESSURE TREATED 2"X4" BASE
PLATE SECURED WITH 3"
CONCRETE NAILS OR EQUIVALENT
SPACER -SAME THICKNESS AS
WALL FINISH MATERIAL
CONCRETE BASEMENT SLAB
AMERICAN GEOSERVICES
FIGURE 7: TYPICAL DETAILS
FLEXIBLE ADHESIVE EQUIVALENT,
4' ABOVE GROUND;
MAINTAIN LEAK -FREE
LEAK -FREE AND ADEQUATE
CAPACITY DOWNSPOUTS
MINIMUM 3' THICK -
DECORATIVE GRAVEL,
ROCK OR BARK LAYER
AT LEAST 4 FT LONG
20 MIL THICK POLY
SHEET LINER AT LEAST
4FT LONG; EXTEND 4'
ABOVE GROUND & 36"
BELOW GROUND
EXTEND DOWNSPOUT
BEYOND
DECORATIVE LAYER,
10H:1 V GRADE;
WITHOUT CAUSING
ADVERSE IMPACT
ON ADJACENT
PROPERTIES; DISCHARGE
ONTO SPLASH BLOCKS.
6"MIN (--
DOWNSPOUT & MOISTURE BARRIER DETAIL
COMPACTED EARTH BACKFIWSOIL CAP
(DO NOT USE IF STEM WALL IS
DESIGNED AS A RETAINING WALL IN
CASE OF RETAINING WALL, USE
FREE -DRAINING CRUSHED ROCK FILL TO
AVOID HYSROSTATIC PRESSURE.
FOUNDATION/STEM WALL
POLYETHYLENE FILM GLUED TO
FOUNDATION WALL AND EXTENDED
BELOW THE DRAIN AS SHOWN
‘..,SLAB -ON -GRADE WITH
EXPANSION JOINTS OR CRAM -SPACE-)
OVER -EXCAVATION
(SEE NOTE B)
1
t.,SUBGRADE, IN -SITU SOIL
(SEE NOTE C)
` OFFSET FOR ANY
SPRINKLER
HEADS; PART CIRCLE
SPRAYING
AWAY FROM BUILDING
SLOPE TO DRAIN AWAY
FROM STRUCTURE, 10H:1 V
(SEE DOWNSPOUT DETAIL)
MIRAFI 140 N FILTER
FABRIC OR EQUIVALENT
FREE -DRAINING
CLEAN CRUSHED
ROCK/GRAVEL
PERIMETER OR FOUNDATION DRAIN DETAIL
EXCAVATED TRENCH,
NEAR VERTICAL TO
0 5H:1V
NOTES: A 4-INCH DIAMETER PERFORATED PIPE PLACED 2' ABOVE DRAIN SUBGRADE EMBEDDED IN FREE -DRAINING GRAVEL OR
CRUSHED ROCK ENVELOPE WITH 2% GRADE TO SUMP PIT OR DISCHARGED TO A SUITABLE RECEPTACLE SUCH THAT ON -SITE AS
WELL AS OFF -SITE STABILITY IS NOT ADVERSELY IMPACTED. B. DEPTH BASED ON OPEN HOLE INSPECTION, FOR SHALLOW
FOUNDATION OPTION C. ALL FOUNDATION OR OVER -EXCAVATED SUBGRADES MUST BE INSPECTED AND APPROVED BY A
GEOTECHNICAL ENGINEER.
1 AMLRICAN G).OSL:RVICIS
FIGURE 8: DRAINAGE DETAILS
APPENDIX
B1
Project Number 0 1 -
Drill Rig CME55 Solid Stem Auger. 4" Diameter
Geologist/Engineer SMA
Ground Elevation See Figures
Date Drilled 0 - 7-20
Total Depth of Borehole Feet
Borehole Diameter 4 OD Inches
Depth to Water Not Encountered
Graphic Log
Description I Lithology
Depth (feet)
m
CI.
E
SPT Blow Couni
Recovery (%)
Moisture (%)
DD (pcf)
LL (%), PL (%)
Swell (%)
c
0
CD
o.
o
W
^ —�f
— 5-
_ _
_ _
_ _
— _
'
i
-11-1
_
0
0
j{
\,
F
>(
^.___
]A,4 r•
]eh
-,
[�
,
:.i
t
End of Borehole
Groundwater was not encountered
during or at the completion of drilling.
At completion, borehole was backfilled
with soil cuttings.
— _
— _
—10
1....... _AM,,..- .� CR CAN G..=CS1.. RVICLS
Page 1
AMERICAN
V GEOSERVICES
DESCRIPTIVE TERMINOLOGY & SOIL CLASSIFICATION
UNIFIED SOIL CLASSIFICATION SYSTEM
UNIFIED SOIL CLASSIFICATION AND SYMBOL CHART
LABORATORY CLASSIFICATION CRITERIA
COARSE -GRAINED SOILS
(mom :Nan 30% of material Is huger than No. 2OC meye okra.)
GRAVELS
More than 50%
of coarse
fraction larger
than No 4
sieve size
paan Gravels (Less van 5% fines)
GW
R per,
Well -graded gravels, gravel -sand
matures, little or no fines
GW
D6o pSl
Cu greater than 4, Co - betvnten 1 and 3
D10
DDOx08p
Poorly -graded gravels, gravel -sand
matures, little or no fines
Gonna wi h flees Wort than 12% 1Lng51
GP Not meeting al gradation requirements for GW
GM
Silty gravels, gravel -sand -silt n ixlsres
1i GC
Peen Sanaa (Leas Elton 5% 10resl
SW
SANDS
50% or more
of coarse
fraction smaller
than No. 4 r
sieve size k`
Clayey gravels, gravel -sand -clay
mixtures
6M Atterberg limits below "A"
line or P.I. less than 4
GC Affarberg 6111i0 aborr'A
tun WM P.I. greater then 7
Above' A' ine with P.I between
4 and 7 are borderline rases
requiring use of dual symbols
Well -graded sands, gravelly sands,
tittle or no fines
SW
Cu= - treater than 4
D tD
D
Co = - between 1 and 3
0100D60
SP
Poorly graded sands, gravelly sands,
little or no fines
Sandm met that SMorerflan12% tines!
SM
Silty sands, sand -silt mixtures
sP Not meeting all gradation requiremenls for GW
SM Atlerberg limits below 'A'
line or P.I less than 4
SC
Clayey sands, sand -clay mixtures
Atiarwerg *Ng six.* Yne woh P.I. gib than
7
Limits plotting in shaded zone
with P.I between 4 and 7 are
borderline cases requiting use
of dual symbols
FINE-GRAINED SOILS
(50% or more of malanal is smaller than No 200 Nevea,e)
SILTS
AND
CLAYS
Liquid lima
less than
50%
ML
Inorganic silts and very fine sands, rock
flour, silty of eieyeyrine panda or ttay5
SIM eat sight plos6cily
CL
Inorganic clays of low to medium
plasticity, gravelly days, sandy days,
silty days, lean clays
Determine percentages or send and gravel 1nam grain -size curve. Depending
on percentage of tines (traction smaller than No 200 sieve size),
coarse -grained soils are classified as follows:
Less than 5 percent GW, GP, SW, SP
More than 12 percent GM, GC, SM, SC
5 to 12 percent Borderline cases requiring dual symbols
PLASTICITY CHART
OL
Organic sills and organic slty days of
low plasticity
SILTS
AND
CLAYS
Liquid limit
50%
or greater
MH
inorganic sila, micaceous or
6istoseseixis anew,* or silty soils,
elastic silts
CH
Inorganic days of high plasticity, fat
days
• OH
Organic days of medium to high
plasticity, organic sat
HIGHLY
ORGANIC PT
SOILS
Peat and other highly organic soils
60
F 50
rX 4030
0
5-
r
U 20
a 10
0
CH
ALINE;
PI • D
796J--20)
CL
)
MH&OH
�--,1
M//
10 20 30 40 50 60 70 80 90 100
LIQUID LIMIT (LL) (%)
DESCRIPTIVE TERMINOLOGY & SOIL CLASSIFICATION
LABORATORY/FIELD TESTING DEFINITIONS FOR CONSISTENCY OF COHESIVE SOILS
EXPLORATION LOGS
DD = DRY DENSITY (PCF)
WD • WET DENSITY (PCF)
MC • MOISTURE CONTENT (%)
PL = PLASTIC LIMIT (%)
LL * LIQUID LIMIT (%)
PI a PLASTICITY INDEX
OC • ORGANIC CONTENT (%)
$$ • SATURATION PERCENT(%)
SG • SPECIFIC GRAVITY
C • COHESION
m • ANGLE OF INTERNAL FRICTION
QU 44- UNCONFINED COMPRESSION
STRENGTH
4200 • PERCENT PASSING THE 6200 SIEVE
CBR • CALIFORNIA BEARING RATIO
• VANE SHEAR
VS
PP
DP
= POCKET PENETROMETER
• DRIVE PROBE
SPT • STANDARD PENETRATION TEST
BPF • BLOWS PER FOOT (N VALUE)
SH • SHELBY TUBE SAMPLE
GW • GROUND WATER
ROD • ROCK QUALITY DESIDNATION
TP
B
HA
• TEST PIT
• BORING
• HAND AUGER
GROUNDWATER LEVEUSEEPAGE
ENCOUNTERED DURING EXPLORATION
STATIC GROUNDWATER LEVEL WITH
DATE MEASURED
CONSISTENCY
VERY SOFT
SOFT
MEDIUM STIFF
STIFF
VERY STIFF
HARD
STP (BPF)
0-1
2-4
5-6
9-15
16-30
30+
PP (TSF)
LESS THAN 0.25
0.25 - 0.5
05 -1.0
1.0 - 2-0
2-0 - 4.0
OVER 4.0
RELATIVE DENSITY OF COHESIONLESS SOILS
DENSITY
VERY LOOSE
LOOSE
MEDIUM DENSE
DENSE
VERY DENSE
PARTICLE SIZE IDENTIFICATION
NAME
ROCK BLOCK
BOULDER
COBBLE
GRAVEL
COURSE
FINE
SAND
COARSE
MEDIUM
FINE
SILT
CLAY
GRAIN SIZE
FINE
GRAINED
MEDIUM
GRAINED
COARSE
GRAINED
DIAMETER
(INCHES)
>120
12-120
3-12
3/4-3
1/4 - 3/4
475 MM
2 OMM
425 MM
075 MM
<0.005 MM
<0.04 INCH
0 04-0 2 INCH
0.04-0.2 INCH
SPT (BPF)
0-4
5-10
11 - 30
31 - 50
50+
SIEVE NO
NO 4
NO 10
NO 40
NO 200
FEW GRAINS ARE
DISTINGUISHABLE IN THE
FIELD OR WITH HAND LENS
GRAINS ARE
DISTINGUISHABLE WITH THE
AID OF A HAND LENS.
MOST GRAINS ARE
DISTINGUISHABLE WITH THE
NAKED EYE-
DESCRIPTIVE TERMINOLOGY & SOIL CLASSIFICATION
SPT EXPLORATIONS:
STANDARD PENETRATION TESTING IS
PERFORMED BY DRIVING A 2— INCH 0 D SPLIT -
SPOON INTO THE UNDISTURBED FORMATION AT
THE BOTTOM OF THE BORING WITH REPEATED
BLOWS OF A 140 — POUND PIN GUIDED HAMMER
FALLING 30 INCHES. NUMBER OF BLOWS (N
VALUE) REQUIRED TO DRIVE THE SAMPLER A
GIVEN DISTANCE WAS CONSIDERED A MEASURE
OF SOIL CONSISTENCY-
SH SAMPLING:
SHELBY TUBE SAMPLING IS PERFORMED WITH A
THIN WALLED SAMPLER PUSHED INTO THE
UNDISTURBED SOIL TO SAMPLE 2 0 FEET OF
SOIL
AIR TRACK EXPLORATION:
TESTING IS PERFORMED BY MEASURING RATE
OF ADVANCEMENT AND SAMPLES ARE
RETRIEVED FROM CUTTINGS
HAND AUGUR EXPLORATION:
TESTING IS PREFORMED USING A 325'
DIAMETER AUGUR TO ADVANCE INTO THE EARTH
AND RETRIEVE SAMPLES -
DRIVE PROBE EXPLORATIONS:
THIS 'RELATIVE DENSITY' EXPLORATION DEVICE
IS USED TO DETERMINE THE DISTRIBUTION AND
ESTIMATE STRENGTH OF THE SUBSURFACE SOIL
AND DECOMPRESSED ROCK UNITS. THE
RESISTANCE TO PENETRATION IS MEASURED IN
BLOWS-PER-1/2 FOOT OF AN 11-POUND HAMMER
WHICH FREE FALLS ROUGHLY 3.5 FEET DRIVING
THE 0.5 INCH DIAMETER PIPE INTO THE GROUND.
FOR A MORE DETAILED DESCRIPTION OF THIS
GEOTECHNICAL EXPLORATION METHOD, THE
SLOPE STABILITY REFERENCE GUIDE FOR
NATIONAL FORESTS IN THE UNITED STATES,
VOLUME I, UNITED STATES DEPARTMENT OF
AGRICULTURE, EM-7170-13, AUGUST 1994, P. 317-
321.
CPT EXPLORATION:
CONE PENETROMETER EXPLORATIONS CONSIST
OF PUSHING A PROBE CONE INTO THE EARTH
USING THE REACTION OF A 20-TON TRUCK THE
CONE RESISTANCE (QC) AND SLEEVE FRICTION
(FS) ARE MEASURED AS THE PROBE WAS
PUSHED INTO THE EARTH THE VALUES OF QC
AND FS (IN TSF) ARE NOTED AS THE LOCALIZED
INDEX OF SOIL STRENGTH
ANGULARITY OF GRAVEL & COBBLES
ANGULAR
SUBANGULAR
SUBROUNDED
ROUNDED
COARSE PARTICLES HAVE SHARP
EDGES AND RELATIVELY PLANE SIDES
WITH UNPOLISHED SURFACES.
COARSE GRAINED PARTICLES ARE
SIMILAR TO ANGULAR BUT HAVE
ROUNDED EDGES
COARSE GRAINED PARTICLES HAVE
NEARLY PLANE SIDES BUT HAVE WELL
ROUNDED CORNERS AND EDGES
COARSE GRAINED PARTICLES HAVE
SMOOTHLY CURVED SIDES AND NO
EDGES.
SOIL MOISTURE MODIFIER
DRY ABSENCE OF MOISTURE; DUSTY, DRY
TO TOUCH
MOIST DAMP BUT NO VISIBLE WATER
WET VISIBLE FREE WATER
WEATHERED STATE
FRESH
SUGHTLY
WEATHERED
MODERATELY
WEATHERED
HIGHLY
WEATHERED
COMPLETELY
WEATHERED
RESIDUAL SOIL
NO VISIBLE SIGN OF ROCK MATERIAL
WEATHERING; PERHAPS SLIGHT
DISCOLORATION IN MAJOR
DISCONTINUITY SURFACES.
DISCOLORATION INDICATES
WEATHERING OF ROCK MATERIAL AND
DISCONTINUITY SURFACES. ALL THE
ROCK MATERIAL MAY BE DISCOLORED
BY WEATHERING AND MAY BE
SOMEWHAT WEAKER EXTERNALLY
THAN ITS FRESH CONDITION.
LESS THAN HALF OF THE ROCK
MATERIAL IS DECOMPOSED AND/OR
DISINTEGRATED TO SOIL, FRESH OR
DISCOLORED ROCK IS PRESENT EITHER
AS A CONTINUOUS FRAMEWORK OR AS
CORE STONES.
MORE THAN HALF OF THE ROCK
MATERIAL IS DECOMPOSED AND/OR
DISINTEGRATED TO SOIL FRESH OR
DISCOLORED ROCK IS PRESENT EITHER
AS DISCONTINUOUS FRAMEWORK OR
AS CORE STONE.
ALL ROCK MATERIAL IS DECOMPOSED
AND/OR DISINTEGRATED TO SOIL THE
ORIGINAL MASS STRUCTURE IS STILL
LARGELY INTACT.
ALL ROCK MATERIAL IS CONVERTED TO
SOIL THE MASS STRUCTURE AND
MATERIAL FABRIC IS DESTROYED
THERE IS A LARGE CHANGE IN VOLUME,
BUT THE SOIL HAS NOT BEEN
SIGNIFICANTLY TRANSPORTED.
Map Unit Description: Evanston loam, 6 to 25 percent slopes —Aspen -Gypsum Area,
Colorado, Para ai Eagle. Gortlein, ara Patdn Counties
Aspen -Gypsum Area, Colorado, Parts of Eagle,
Garfield, and Pitkin Counties
39--Evanston loam, 6 to 25 percent slopes
Map Unit Setting
National map unit symbol: jq5v
Elevation: 6,500 to 8,000 feet
Mean annual precipitation: 13 to 15 inches
Mean annual air temperature: 42 to 46 degrees F
Frost -free period: 80 to 90 days
Farmland classification: Not prime farmland
Map Unit Composition
Evanston and similar soils: 85 percent
Minor components: 15 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Evanston
Setting
Landform: Alluvial fans, terraces, valley sides
Landform position (three-dimensional): Tread
Down -slope shape: Linear
Across -slope shape: Linear
Parent material: Mixed alluvium
Typical profile
H1 - 0 to 14 inches: loam
H2 - 14 to 31 inches: day loam
H3 - 31 to 60 inches: loam
Properties and qualities
Slope: 6 to 25 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: High
Capacity of the most limiting layer to transmit water (Ksaf):
Moderately high (0 20 to 0 60 inlhr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 10 percent
Available water storage in profile: High (about 10 1 inches)
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 6e
Hydrologic Soil Group: C
Other vegetative classification: DEEP LOAM (null_11)
Hydric soil rating: No
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/a/2020
Page 1 of 2
Map Unit Description: Evanston loam, 6 to 25 percent slopes —Aspen -Gypsum Area, Map Unit Description: Redrob loam, 1 to 6 percent slopes —Aspen -Gypsum Area, Colorado,
Colorado, Parts of Eagle, Garfield, and Pitkin Counties Parts of Eagle, Garfield, and Pitkin Counties
Minor Components
Other soils
Percent of map unit: 15 percent
Hydric soil rating: No
Data Source Information
Soil Survey Area: Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and
Pitkin Counties
Survey Area Data: Version 11, Jun 5, 2020
Aspen -Gypsum Area, Colorado, Parts of Eagle,
Garfield, and Pitkin Counties
92—Redrob loam, 1 to 6 percent slopes
Map Unit Setting
National map unit symbol: jq7r
Elevation: 5,800 to 7,200 feet
Mean annual precipitation: 16 to 18 inches
Mean annual air temperature: 40 to 44 degrees F
Frost -free period: 85 to 105 days
Farmland classification: Not prime farmland
Map Unit Composition
Redrob and similar soils: 85 percent
Minor components: 15 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Redrob
Setting
Landform: Terraces, valley floors, flood plains
Landfonn position (three-dimensional): Tread
Down -slope shape: Linear
Across -slope shape: Linear
Parent material: Mixed alluvium derived from sandstone and shale
Typical profile
H1 - 0 to 14 inches: loam
H2 - 14 to 20 inches: stratified loamy sand to stony loam
H3 - 20 to 60 inches: extremely cobbly loamy sand
Properties and qualities
Slope: 1 to 6 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Somewhat poorly drained
Runoff class: Low
Capacity of the most limiting layer to transmit water (Ksat):
Moderately high to high (0.60 to 2.00 in/hr)
Depth to water table: About 18 to 48 inches
Frequency offlooding: Rare
Frequency of ponding: None
Calcium carbonate, maximum in profile: 10 percent
Salinity, maximum in profile: Nonsaline to very slightly saline (0 0
to 2 0 mmhos/crn)
Available water storage in profile: Low (about 4.3 inches)
Interpretive groups
Land capability classification (irrigated): 4w
Land capability classification (nonirrigated): 4w
Hydrologic Soil Group: C
s� Natural Resources Web Soil Survey 7litr25 xetwa Ralollises Web Soil Survey 7/8/2020
Conservation Service National Cooperative Soil Survey Page 2 of 2 Conservation Service National Cooperative Soil Survey Page 1 of2
Map Unit Description: Redrob loam, 1 to 6 percent slopes —Aspen -Gypsum Area, Colorado,
Parts of Eagle, Garfield, and Pitkin Counties
Ecological site: River Bottom (R048AY236C0)
Other vegetative classification: riverbottom (null_19)
Hydric soil rating: No
Minor Components
Fluvaquents
Percent of map unit: 10 percent
Landform: Flood plains
Hydric soil rating: Yes
Other soils
Percent of map unit: 5 percent
Hydric soil rating: No
Data Source Information
Soil Survey Area: Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and
Pitkin Counties
Survey Area Data: Version 11, Jun 5, 2020
USDA Natant! ri%orrces
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
7/6/2020
Page 2 of 2
IMPORTANT INFORMATION ABOUT YOUR
GEOTECHNICAL ENGINEERING REPORT
As the client of a consulting geotechnical
engineer, you should know that site subsurface
conditions cause more construction problems than
any other factor ASFFJthe Association of
Engineering Firms Practicing in the Geosciences
offers the following suggestions and observations
to help you manage your risks.
A GEOTECHNICAL ENG.NEERING REPORT IS
BASED ON A UNIQUE SET OF PROJECT -
SPECIFIC FACTORS Your geotechnical
engineering report is based on a subsurface
exploration plan designed to consider a unique set
of project -specific factors. These factors typically
include: the general nature oFthe atrticture
involved, its size, and configuration; the location of
the structure on the site; other improvements, such
as access roads, parking lots, and underground
utilities; and the additional risk created by scope -
of -service [Imitations imposed by the client. To
help avoid cosily problems, ask your geotechnical
engineer to evaluate how factors !hat change
subsequent to the date of the report may affect the
reports recommendations.
Unless your geotechnical engineer indicates
otherwise, do not use your geotechnical
engineering report:
MOST GEOTECHNICAL FINDINGS ARE
PROFESSIONAL JUDGMENTS
Site exploration identifies actual subsurface
conditions only at those points where samples are
taken The data were extrapolated by your
geotechnical engineer who then applied judgment
to render an opinion about overall subsurface
conditions. The actual interface between materials
may be far more gradual or abrupt than your
report indicates, Actual conditions in areas not
sampled may differ from those predicted in your
report. While nothing can be done to prevent such
situations. you and your geotechnical engineer
can work together to help minimize their impact.
Retaining your geotechnical engineer to observe
construction can be particularly beneficial in this
respect.
• when the nature of the proposed structure is
changed. for example, if an office building will
be erected instead of a parking garage. or a
refrigerated warehouse will be built instead of
an unrefrigerated one;
• when the size, elevation. or configuration of the
proposed structure is altered
• when the location or orientation of the proposed
structure is modified;
• when there is a change of ownership; or .for
application to an adjacent site.
Geotechnical engineers cannot accept
responsibility for problems That may occur if they
are not consulted after factors considered in their
reports development have changed.
A REPORTS RECOMMENDATIONS CAN ONLY
BE PRELIMINARY
The construction recommendations included in
your geotechnical engineer's report are
preliminary, because they must be based on the
assumption that conditions revealed through
selective exploratory sampling are indicative of
actual conditions throughout a site.
Because actual subsurface conditions can be
discemed only during earthwork, you should retain
your geo- technical engineer to observe actual
conditions and to finalize recommendalions. Only
the geolechnical engineer who prepared the report
is fully familiar with the background information
needed to determine whether or not the report's
recommendations are valid and whether or not the
contractor is abiding by applicable
recommendations. The geotechnical engineer who
developed your report cannot a ssrtme
responsibility or liability for the adequacy of the
reports recommendations if another party is
retained to observe construction
SUBSURFACE CONDITIONS CAN CHANGE A
geotechnical engineering report is based on condi-
tions that existed at the time of subsurface
exploration. Do not base construction decisions on
a geotechnical engineering report whose
adequacy may have been affected by time. Speak
with your geotechnical consult- ant to learn if
additional rests are advisable before construction
starts. Note, too, that additional tests may be
required when subsurface condition are affected
by construction operations at or adjacent to the
site, or by natural events such as floods,
earthquakes, or ground water fluctuations. Keep
your geotechnical consultant apprised of any such
events.
GEOTECHNICAL SERVICES ARE PERFORMED
FOR SPECIFIC PURPOSES AND PERSONS
Consulting geotechnical engineers prepare reports
to meet the specific needs of specific individuals. A
report prepared for a civil engineer may not be
adequate for a construction contractor or even
another civil engineer. Unless indicated otherwise,
your geotechnical engineer prepared your report
expressly for you and expressly for purposes you
indicated. No one other than you should apply this
report for its intended purpose without first
conferring with the geotechnical engineer No
party should apply this report for any purpose
other than that anginal). conlernplated without first
conferring with the geotechnical engineer
GEOENVIRONMENTAL CONCERNS ARE NOT
AT ISSUE
Your geotechnical engineering report is not likely
to relate any findings, conclusions, or
recommendations
about the potential for hazardous materials
existing at the site. The equipment, techniques,
and personnel used to perform a
geoenvironmental exploration differ substantially
from (hose applied in geolechnical engineering.
Contamination can create major risks. If you have
no information about the potential for your site
being contaminated. you are advised to speak with
yourgeotechnicalconsultant for information
relating to geoenvironmental issues.
A GEOTECHNICAL ENGINEERING REPORT IS
SUBJECT TO MISINTERPRETATION Costly
problems can occur when other design profes-
sionals develop their plans based on
misinterpretations of a geotechnical engineering
report 1 o help avoid misinterpretations, retain
your geotechnical engineer to work with other
project design professionals who are affected by
the geotechnical report. Have your geolechnlcal
enginec-r explain report implications to design
professionals affected by them and then review
those design professionals' plans and
specifications to see how they have incorporated
geotechnical factors Although certain other design
professionals may be fam- iliar with geotechnical
concems, none knows 'as much about them as a
competent geotechnical engineer.
BORING LOGS SHOULD NOT BE SEPARATED
FROM THE REPORT Geotechnical engineers
develop final boring logs based upon their
interpretation of the field logs
(assembled by site personnel) and laboratory
evaluation of field samples. Geotechnical
engineers customarily include only final boring
logs in their reports. Final boring logs should not
under any circumstances be redrawn for inclusion
in architectural or other design drawings. because
drafters may commit errors or omissions in the
transfer process. Although photographic
reproduction eliminates this problem, it does
nothing to minimize the possibility of contractors
misinterpreting the logs during bid preparation.
When this occurs. delays disputes. and
unanticipated costs ara the all -too -frequent result.
To minimize the likelihood of boring log
misinterpretation, give contractors ready access to
the complete geotechnical engineering report
prepared or authorized for their use. (If access is
provided only to the report prepared for you, you
should advise contractors of the reports
limitations. assuming that a contractor was not one
of the specific persons for whom the report was
prepared and that developing
construction cost estimates was not one of the
specific purposes for which it was prepared. In
other words. while a contractor may gain important
knowledge from a report prepared for another
party, the contractor would be well-advised to
discuss the report with your geotechnical engineer
and to perform the additional or alternative work
that the contractor believes may be needed to
obtain the data specifically appropriate for
construction cost estimating purposes.) Some
clients believe that it is unwise or unnecessary to
give contractors arcPes to their geo- technical
engineering reports because they hold the
mistaken impression that simply disclaiming
responsibility for the accuracy of subsurface
information always insulates them from attendant
liability. Providing the best available information to
contractors helps prevent costly construction
problems It also helps reduce the adversarial
attitudes that can aggravate problems to
disproportionate scale.
READ RESPONSIBIIJTY CLAUSES CLOSELY
Because geotechnical engineering is based
extensively on judgment and opinion, it is far less
exact than other design disciplines. This situation
has resulted in wholly unwarranted claims being
lodged against geotechnical engineers. To help
prevent this problem, geotechnical engineers have
developed a number of clauses for use in their
contracts, reports, and other documents.
Responsibility clauses are not exculpatory clauses
designed to Itansfer geolechnical engineers'
liabilities to other parties. Instead, they are
definitive clauses that identify where geotechnical
engineers' responsibilities begin and end. Their
use helps all parties involved recognize their
individual responsibilities and take appropriate
action. Some of these definitive clauses are likely
to appear in your geotechnical engineering report.
Read them closely. Your geotechnical engineer
will be pleased to give full and frank answers to
any questions
RELY ON THE GEOTECHNICAL ENGINEER
FOR ADDITIONAL ASSISTANCE
Most ASFE-member consulting geotechnical
engineering firms are familiar with a variety of
techniques and approaches that can be used to
help reduce risks for all parties to a construction
project, from design through construction. Speak
with your geotechnical engineer not only about
geotechnical issues, but others as well, to team
about approaches that may be of genuine benefit.
You may also wish to obtain certain ASFE
publications. Contact a member of ASFE of ASFE
for a complimentary directory of ASFE
publications.
ASFE
8811 Colesville Road/Suite G106/Silver Spring, MD 20910
Telephone: 301/565-2733 Facsimile: 301 /589-2017
Subsurface Explorations
Soil Testing
Earthwork Monitoring
Geotechnology
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Rock Mechanics
Earthquake Engineering
Geophysics
Retaining Wall Design
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