HomeMy WebLinkAboutSoils Report 03.28.2020AMERJ CAN
GEOSERVICES
Geotechnical Evaluation Report
50 Larkspur Drive, Carbondale, CO
Date: March 28, 2020
Project No: 0137-CS20
AMERICAN
GEOSERVICES
GEOTECHNICAL & MATERIALS
ENVIRONMENTAL
STRUCTURAL
CIVIL
ENGINEERING AND SCIENCE
888-276-4027
March 28, 2020
PROJECT NO: 0137-CS20
CLIENTS: Mr. Gavin Marlino
Reference: Soil Testing / Lot -specific Geotechnical Evaluation, 50 Larkspur Rd, Carbondale, CO
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, except for
the proposed walkout basement. We anticipate proposed structure will be constructed with light
to moderate foundation Toads.
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 March 2020, we performed soil explorations (B1-B2) at approximate location 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 10 feet below existing ground surface (BGS)
where very difficult drilling was encountered. 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
1338 Grand Avenue #306
Glenwood Springs, CO 81601
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encountered at the site are included in 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 an irregularly -shaped parcel of land. Currently the site topography is gently to
moderately sloping downwards to the south towards the creek. At the time of our site visit, there
was no visual indication of active slope instability or active landslides in the proposed
construction area. Surficial rock outcrops or boulders were noted at sporadic locations.
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 Iithological 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.
Surface Conditions: Approximately 6 inches mixtures of topsoil, loam, sand, and root mass is
present at the surface.
Silty Sand to Sand with Gravel/Cobble (Alluvium): Site is primarily underlain by low -plasticity
mixtures of sand, silt, clay, gravel, pebble, and some rock/cobble pieces (SM/GM) extending to a
maximum depth of about 2.5 feet. These soils have a relative density of medium dense near the
surface to mostly dense.
Clayey Silt to Silty Clay (Colluvium) with Gravel: These soils appeared to have been derived
from complete weathering and erosion of local calcareous sandstone/mudstone and/or
calcareous shale of the Eagle Valley Formation. Colluvium is known to extend to at least 5-7
feet in the site vicinity area where it is underlain by the local bedrock (Figure 3). Refusal to
angering was encountered at a depth of about 10 feet in offsets taken at the site for boreholes.
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Completely Weathered Eagle Valley Formation: Below 5-7 feet, site is generally underlain by
completely weathered local bedrock. Within this soil/rock stratum, it is possible to encounter
cobbles and/or boulders/clasts of varying sizes.
Groundwater: Groundwater was not encountered at the 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.
GEOLOGIC HAZARDS EVALUATION
Evaporite Sinkholes: Site is located in general vicinity of the Eagle Valley Evaporite. The
evaporite between Carbondale and about 3 miles south of Glenwood Springs is part of the
Roaring Fork diaper which meets with the Grand Hogback monocline. This marks the western
limit of the Carbondale evaporite collapse center. The Carbondale evaporite collapse center is
the western collapse center among the two in the western Colorado evaporite region. Up to a
possible 4,000 feet of regional ground subsidence may have occurred during the past 10 million
years resulting from dissolution and evaporite flowage from beneath the region. Data cannot
show whether the regional subsidence and evaporite deformation along the Roaring Fork diaper
are still an active geomorphic process or if the evaporite deformations have stopped. If the
evaporite deformation is still active, current deformations are most probably occurring at rates
similar to long-term rates of the past, between 1.0 and 2.0 inches per 100 years. Due to the slow
or unmoving nature of the deformations, AGS does not consider them a risk to future
developments at the project site.
At the time of our site visit, we did not notice any visual evidence of sinkholes at the site or adjacent
to site boundaries. Evaporite sinkholes in western Colorado are typically 10ft to 50ft diameter,
circular depressions at the ground surface that result from upward caving of a soil rubble pipe to
the ground surface. The soil rubble pipe is formed by subsurface erosion (piping) of near surface
soils into subsurface voids. Sinkhole development or reactivation in the area is still an active
geomorphic process. The owner should understand and assume the risk of future sinkhole
development, although, in our opinion, the potential for future sinkhole development is low,
provided proper drainage is maintained at the site. No warranty is expressed unless a
comprehensive geologic hazards assessment of the site as well as site vicinity is performed.
Expansive Soils and Bedrock: The site is possibly underlain by low to moderate expansive
clayey soils or clayey sedimentary bedrock materials. Moreover, local pockets of expansive
clayey materials can occur through the site and may cause heave in the flatwork around the site.
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This is typical of many areas in Colorado. Therefore, an open -hole inspection performed by a
geotechnical engineer is very important for this site to minimize the expansive soils/bedrock
hazard.
Flooding: Our review of available flood hazards map and literature did not indicate that the site
is susceptible to flooding due to river, and perennial and intermittent tributaries across the project
area. Notwithstanding, a detailed flood hazard evaluation was beyond our scope of services. We
recommend hiring an experienced hydrologist to evaluate the flood hazards for the site.
Debris Flow: Site is not located within alluvial fans or flood channels. However, in the site vicinity,
several ancient debris flow deposits are present. Although debris flow hazard at the site is minimal
under normal site, topographic, geologic, and weather conditions, the owner should understand
future possible risks from debris flow occurring in the site vicinity. No warranty is expressed
unless a comprehensive geologic hazards assessment of the site as well as site vicinity is
performed.
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 landslides had occurred at the site or immediately adjacent to the site. Landslide deposits
are not located within 100 feet of the site boundaries. 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. During our reconnaissance, there was no visual evidence of active global slope
instability or active global landslides that would adversely impact site stability in the immediate
site vicinity.
Notwithstanding, the northern portion of the site vicinity is possibly located in the landslide
hazards, and there is a potential for future slope stability in the northern site vicinity. Moreover,
ancient landslide deposits are known to be present in general site vicinity, suggesting that there
have been localized landslides in the site vicinity. Considering these site vicinity conditions, in
our opinion, there is a low to moderate landslide hazard that the owner should be aware of,
although this hazard is applicable to the site vicinity, in general.
Considering these findings, it is our opinion that the site and the immediate vicinity area have
`inherent' risk associated with slope instability and impact from the movement of any
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global/ancient landslide and local slope movements, however, there is minimal 'impending' risk
of ground movement. It should also be noted that, considering the scale of the area and the
hazard involved, the site (or any adjacent or nearby properties) cannot be engineered for global
slope stability.
Historically. with construction in such areas, there is always an 'inherent' and 'high' risk associated
with ground movement and/or settlements and/or soil creep and related structural damage. The
owner should understand these inherent risks. It should be noted that the detailed evaluation of
the impact of any undiscovered ancient or global landslides (if any) in the site vicinity area was
beyond our scope of services.
The landslide terrain and the vicinity area are such that, under normal conditions, there exists
some potential for a future global slope failure, based on the slopes, distance to the fault zones,
local geology, and especially if excessive cuts or grading or roads or extensively modifications of
the terrain by anthropogenic activity, and forest loss occurs. In our opinion, the life safety risk to
the occupants from such a slide can be accurately determined only by performing an extensive
study involving extensive subsurface explorations, installation of inclinometers, detailed slope
There has been a certain amount of variability in legal interpretations of liability of geotechnical
engineers and geologists in regard to landslide -related losses; but the conclusions reached are
general in nature and not necessarily valid in any specific court. Liability of geotechnical engineers
and engineering geologists for landslide damages to home sites is based most often on the theory
of negligence and occasionally on negligent misrepresentation. Although allegations seeking to
recover damages from geotechnical engineers and geologists on the basis of strict liability, breach
of warranty, or intentional misrepresentation are often included in a complaint, they are not usually
applicable or valid under normal circumstances. All private property owners should make a note
of this.
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
in the proposed construction area, provided site drainage is properly maintained during the design
life 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 SLOPE/W 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 SLOPE/W computer software calculates the most likely failure plane based on topography,
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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
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 life of the structure.
Inherent Slope Instability Risks: Historically, with construction in hilly or mountainous areas,
there is an inherent risk associated with slope failures. Although there was no slope instability
observed within the building envelope or adjacent to the site boundaries, and the potential for
future slope failure is extremely 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 site vicinity. 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,
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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 0.1g 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.
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:
• Over -excavate any boulders or large clasts within the foundation areas, any expansive
soils/bedrock from within at least 24 inches of the bottom of footings, then surficial compact
the excavated surface, and then backfill (if necessary) with granular free -draining structural
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fill (or onsite sandy/gravelly soils) compacted to at least 95% of ASTM D698 maximum dry
density in order to achieve a "uniform (non -rocky) subgrade" and to facilitate the placement of
foundation drain. Over -excavation can 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. It should be noted that
an open -hole inspection is critical for this site.
• 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).
• 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 6 should be placed.
• Foundation/stem walls should be adequately designed as retaining walls and adequate
drainage measures should be implemented as shown in Figure 7.
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.
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
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
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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 7 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 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.
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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 7 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 to moderate". 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 expansive soils/bedrock. Proper wetting of the subgrade to
obtain soil moisture content in the range of 20-22% and/or moisture -conditioning and
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, or an over -excavation of at least 24 inches and backfilling with granular structural fill
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.
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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 barrier 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
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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 3 inches of void space (as illustrated in Figure 6) 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 furnace 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 backfill 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
Toads 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 4. Backfill should not be over -compacted in order to
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.
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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 limit 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 such as the walk -out or full basement,
heavier equipment with toothed bucket most likely will be required. Although our soil explorations
did not reveal "buried" foundation elements 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.
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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
prevent the compacted fill from freezing overnight. The "blanket" of loose fill should be removed
the next morning 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 of time passing between
Project No: 0137-CS20
March 28, 2020
Page No: 14 of 17
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 Tong -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 7. 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 not encountered 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
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:1 V
away from foundations. Downspouts from all roof drains, if any, should cross all backfilled areas
Project No: 0137-CS20
March 28, 2020
Page No: 15 of 17
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-term 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.
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 concerned 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.
Project No: 0137-CS20
March 28, 2020
Page No: 16 of 17
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: 0137-CS20
March 28, 2020
Page No: 17 of 17
FIGURES
LE
-' -81 "Carlrandale
REFERENCE: TT
GOOGLE MAPS N
USGS TOPOGRAPHIC MAPS
112))
L' �1 JII
1F7'
ip5[Y Larkspur Drive
1
FI Jebel
SITE LOCATION
rtn,:nlo
a
f.
AMERICAN GEOSERVICES
Basalt 6h Mountain
Basal)
Snowrnass
• 4
FIGURE 1: SITE LOCATION MAP
NOTE:
SCHEMATIC PLAN TO SHOW APPROXIMATE SUBSURFACE EXPLORATION LOCATION ONLY; NOT SURVEYED.
LEC1E ND:
DESIGNATES SUBSURFACE EXPLORATION LOCATION, BY AMERICAN GEOSERVICES, LLC. , MARCH 2020 SEE
EXPLORATION LOG IN APPENDIX FOR FURTHER DETAILS.
N
GARFIELD COUNTY
COLORADO GIS
r AMEI JGAN GEOSERVICES
Vh 8.2]6 4027 on,,iinKio ser, ices tom
FIGURE 2: SCHEMATIC SITE PLAN
[Pee
` Qc
LEGEND
Eagle Valley Evapoiite (Middle Pennsylvanian)—Evaporitic
sequence of gypsum, anhydrite, and halite interbedded
rnudsiune, fine -grainer sandstone, thin carbonate
beds, and black shale. Commonly intensely folded,
faulted, and ductily deformed
Colluvium (Holocene and late Pleistocene) --Ranges from
unsorted, clast-supported, pebble to boulder gravel in a
sandy slit matrix to matrix -supported gravelly, clayey,
sandy silt. Usually coarser grained in upper reaches of
colluvial slope and finer grained in distal areas
Qty
Qdfy
Younger debris -flow deposits (Holocene and late Pleisto-
cene?) --Poorly sorted to moderately well -sorted, matrx-
and clast-supported deposits ranging from gravelly
clayey silt to sandy, silty, cobbly, pebbly, and bouldery
gravel. Fan heads tend to be bouldery, while distal fan
areas are finer grained. Includes debris -flow, hyper -
concentrated -flow, fluvial, and sheetwash deposits on
active fans and in some drainage channels. Numeric
subscripts indicate relative ages of younger debris fan
deposits in the southwest corner of the quadrangle.
Deposits labeled Qdfyi are younger than and derived
from deposits labeled Qdfy2
Younger terrace alluvium (late Pleistocene) —Mostly poorly
sorted, clast-supported, locally bouldery, pebble and
cobble gravel in a sand and silt matrix. Deposited as
glacial outwash. Underlies terraces 15-52 ft above modern
stream level. May include fine-grained overbank deposits
N
REFERENCE:
U.S. GEOLOGICAL MAPS
...sloe_
AMERICAN GEOSERVICES
898.276.4027- amcricangeoserviceseom
FIGURE 3: GEOLOGIC MAP
REFERENCE:
LEGEND
Aspen -Gypsum Area, Colorado, Parts of
Eagle, Garfield, and Pitkin Counties
(C0655)
Map Acres percent
Unit Map Unit Name in of AOI
Symbol AOI
55 Gypsum land- 6,4 30.4°%o
Gypsiorthids
complex, 12 to 65
percent slopes
114 Yamo loam, 1 to 6 3.4 16.5%
percent slopes
115 Yamo loam, 6 to 12 11.1 53,1%
percent slopes
Totals for Area of
Interest
20.9 100.0%
N
WEB SOIL SURVEY
AMERICAN GEOSERVICES
888.27(002i • nmelicnngeoserric,cotn
FIGURE 4: SOIL SURVEY MAP
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 ENGINEER'S
DESIGN. AS A MINIMUM, USE #4 AT 48" C/C.
■
•
a
..
13 v Y
•
.
'1 •
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.
• •
a •
" 1
ADDITIONAL FOOTING REINFORCEMENT DETAIL
NOTES:
NEW INTERIOR
PARTITION 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
•• A
WALL FINISH
MATERIAL
a
PRESSURE TREATED 2"X4" BASE
PLATE SECURED WITH 3"
CONCRETE NAILS OR EQUIVALENT
SPACER -SAME THICKNESS AS
WALL FINISH MATERIAL
A
"FLOAT" (FLOATING WALL DETAIL)
CONCRETE BASEMENT SLAB
f j AMERICAN C,[OSERVICES
VFNN 2'(.Ile7-apwnLunµar,•rSuv+cim
FIGURE 6: TYPICAL DETAILS
SILICON EAL OR HIGH + ALITY
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:1V GRADE;
WITHOUT CAUSING
ADVERSE IMPACT
ON ADJACENT
PROPERTIES; DISCHARGE
ONTO SPLASH BLOCKS.
6"MIN �—
DOWNSPOUT & MOISTURE BARRIER DETAIL
COMPACTED EARTH BACKFILL/SOIL 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 CRAWL -SPACE
twoVer. ell
ff#40- jlt
italterei
1�+�! �l��! �! lid !,�• �` �i
OVER -EXCAVATION r r► � oii w * w � INAIO
(SEE NOTE B) 114 *;4,1 eflk
111 rlll+" l+�►!+!0
11 §,LROMOMO. •I��/
�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:1V
(SEE DOWNSPOUT DETAIL)
MIRAFI 140 N FILTER
FABRIC OR EQUIVALENT
U
12" MIN
" MIN
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
l _ AME RICAN GLOSI=RVIC[S
V?`j. 4 .! - amrncifl tO CYS1CV Cum
FIGURE 7: DRAINAGE DETAILS
APPENDIX
BI -B2
50 Larkspur Drive, Carbondale, CO
Project Number 0137-CS20
Drill Rig: CME55 Solid Stem Auger, 4" Diameter
Geologist/Engineer SMA
Ground Elevation See Figures
Date Drilled 03-15-2020
Total Depth of Borehole 8 Feet
Borehole Diameter 4 OD Inches
Depth to Water Not Encountered
SM/
GM
CU
ML/
GM
•
•
Description / Lithology
to-
t
a
0)
0
a)
E
co
Recovery (%)
0
a
0
J
J
SAND to SILTY SAND with GRAVEL/
COBBLES, medium to fine grain,
brown,dry to damp, medium dense to
dense,
(ALLUVIUM)
SANDY CLAY to SILTY CLAY to CLAYEY
SANDY SILT, some GRAVEL, fine to
coarse grain, brown, some gravel or
weathered rock pieces, very stiff to hard,
damp to moist, low plasticity
(COLLUVIUM)
Completely weathered Sandstone/Mudstone /
Shale
(Possibly Eagle Valley Formation)
End of Borehole.
Groundwater was not encountered during or at
the completion of drilling.
At completion, borehole was backfilled with soil
cuttings.
.-6.0 —
5-14-6
r 9-10-14
50+
--7.5 —
�0 —
80
80
20
30, 2C
1.15%
1000
psf
VAMERICAN GEOSERVICES
8B6276,4027- 4meiir.ry,...crnccs.cum
Page 1
j J AMERICAN
V GEOSERVICES
DESCRIPTIVE TERMINOLOGY & SOIL CLASSIFICATION
UNIFIED SOIL CLASSIFICATION SYSTEM
UNIFIED SOIL CLASSIFICATION AND SYMBOL CHART
COARSE -GRAINED SOILS
(more than 50% of material is larger than No. 200 sieve size.)
GRAVELS
More than 50%
of coarse
fraction larger
than No 4
sieve size
SANDS
50% or more
of coarse
fraction smaller
than No. 4
sieve size
Clean Gravels (Less than 5% fines)
Well -graded gravels, gravel -sand
jai GW mixtures, little or no fines
❑ GP
Poorly -graded gravels, gravel -sand
mixtures, little or no fines
Gravels with fines (More than 12% fines)
GM
i
GC
ss
Silty gravels, gravel -sand -silt mixtures
Clayey gravels, gravel -sand -clay
mixtures
Clean Sands (Less than 5% fines)
SW Well -graded sands, gravelly sands,
little or no fines
SP
Poorly graded sands, gravelly sands,
little or no fines
Sands with fines (More than 12% fines)
SM Silty sands, sand -silt mixtures
SC
Clayey sands, sand -clay mixtures
FINE-GRAINED SOILS
(50% or more of material is smaller than No. 200 sieve size.)
SILTS
AND
CLAYS
Liquid limit
less than
50%
SILTS
AND
CLAYS
Liquid limit
50%
or greater
HIGHLY
ORGANIC
SOILS
MH
CH
OH
Inorganic silts and very fine sands, rock
flour, silty of clayey fine sands or clayey
silts with slight plasticity
Inorganic clays of low to medium
plasticity, gravelly clays, sandy clays,
silty clays, lean clays
Organic silts and organic silty clays of
low plasticity
Inorganic silts, micaceous or
diatomaceous fine sandy or silty soils,
elastic silts
Inorganic clays of high plasticity, fat
clays
Organic clays of medium to high
plasticity, organic silts
Peat and other highly organic soils
LABORATORY CLASSIFICATION CRITERIA
GP Not meeting all gradation requirements for GW
GM
Atterberg limits below "A"
line or P.I. less than 4
GC
Atterberg limits above "A"
line with P.I. greater than 7
Above "A" line with P.I. between
4 and 7 are borderline cases
requiring use of dual symbols
C = D60 greater than 4; C _ D30 between 1 and 3
SW u D 10 c D10 x D60
SP
Not meeting all gradation requirements for GW
SM Atterberg limits below "A"
line or P.I. less than 4
SC
Atterberg limits above "A"
line with P.I. greater than 7
Limits plotting in shaded zone
with P.I. between 4 and 7 are
borderline cases requiring use
of dual symbols.
Determine percentages of sand and gravel from grain -size curve. Depending
on percentage of fines (fraction 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
PLASTICITY INDEX (PI) (%)
60
50
40
30
20
10
0
CH
7
A
PI = 0
LINE'
73(LL-20)
CL
T
MH&OH
�%
aim.
ML&OL
LIQUID LIMIT (LL) (%)
DESCRIPTIVE TERMINOLOGY & SOIL CLASSIFICATION
LABORATORY/FIELD TESTING DEFINITIONS FOR CONSISTENCY OF COHESIVE SOILS
EXPLORATION LOGS
CONSISTENCY STP (BPF) PP (TSF)
DD = DRY DENSITY (PCF) VERY SOFT 0-1 LESS THAN 0.25
SOFT 2 - 4 0.25 - 0.5
WD = WET DENSITY (PCF) MEDIUM STIFF 5 8 0.5 - 1.0
MC = MOISTURE CONTENT (%) STIFF 9 - 15 1.0 - 2.0
PL = PLASTIC LIMIT (%) VERY STIFF 16 - 30 2.0 - 4.0
HARD 30+ OVER 4.0
LL = LIQUID LIMIT (%)
PI = PLASTICITY INDEX RELATIVE DENSITY OF COHESIONLESS SOILS
OC = ORGANIC CONTENT (%) DENSITY SPT (BPF)
5 = SATURATION PERCENT (%) VERY LOOSE 0 - 4
LOOSE 5 - 10
SG = SPECIFIC GRAVITY
MEDIUM DENSE 11 - 30
C COHESION DENSE 31 - 50
4> = ANGLE OF INTERNAL FRICTION VERY DENSE 501.
QU = UNCONFINED COMPRESSION
STRENGTH PARTICLE SIZE IDENTIFICATION
#200 = PERCENT PASSING THE #200 SIEVE NAME DIAMETER SIEVE NO.
CBR = CALIFORNIA BEARING RATIO (INCHES)
VS = VANE SHEAR ROCK BLOCK >120
BOULDER 12-120
PP = POCKET PENETROMETER
COBBLE 3-12
DP = DRIVE PROBE GRAVEL
SPT = STANDARD PENETRATION TEST COURSE 3/4 - 3
FINE 114 -3/4 NO. 4
BPF BLOWS PER FOOT (N VALUE)
SAND
SH = SHELBY TUBE SAMPLE COARSE 4.75 MM NO 10
GW = GROUND WATER MEDIUM 2.0MM NO. 40
FINE .425 MM NO. 200
RQD = ROCK QUALITY DESIDNATION
SILT .075 MM
TP = TEST PIT CLAY <0.005 MM
B BORING
GRAIN SIZE
HA HAND AUGER
FINE <0.04 INCH FEW GRAINS ARE
GRAINED DISTINGUISHABLE IN THE
V FIELD OR WITH HAND LENS.
GROUNDWATER LEVEUSEEPAGE MEDIUM 0.04-0.2 INCH GRAINS ARE
ENCOUNTERED DURING EXPLORATION GRAINED DISTINGUISHABLE WITH THE
AID OF A HAND LENS.
COARSE 0.04-0.2 INCH MOST GRAINS ARE
GRAINED DISTINGUISHABLE WITH THE
STATIC GROUNDWATER LEVEL WITH NAKED EYE.
DATE MEASURED
DESCRIPTIVE TERMINOLOGY & SOIL CLASSIFICATION
SPT EXPLORATIONS:
STANDARD PENETRATION TESTING IS
PERFORMED BY DRIVING A 2 - INCH O.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
RETR►EVED FROM CUTTINGS.
HAND AUGUR EXPLORATION:
TESTING IS PREFORMED USING A 3.25"
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
❑RY
MOIST
WET
WEATHERED STATE
FRESH
SLIGHTLY
WEATHERED
MODERATELY
WEATHERED
HIGHLY
WEATHERED
COMPLETELY
WEATHERED
RESIDUAL SOIL
ABSENCE OF MOISTURE; DUSTY, DRY
TO TOUCH
DAMP BUT NO VISIBLE WATER
VISIBLE FREE WATER
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 15 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: Yamo loam, 6 to 12 percent slopes--Aspen-Gypsum Area, Colorado,
Parts of Eagle, Garfield, and Pitkin Counties
Aspen -Gypsum Area, Colorado, Parts of Eagle,
Garfield, and Pitkin Counties
115—Yamo loam, 6 to 12 percent slopes
Map Unit Setting
National map unit symbol: jq4r
Elevation: 6,200 to 7,500 feet
Mean annual precipitation: 10 to 14 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
Yamo and similar soils: 80 percent
Minor components: 20 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Yamo
Setting
Landform: Fans, mountains
Landform position (three-dimensional): Lower third of
mountainflank
Down -slope shape: Linear
Across -slope shape: Linear
Parent material: Colluvium derived from sandstone and/or
colluvium derived from shale and/or colluvium derived from
gypsum
Typical profile
H1 - 0 to 8 inches: loam
H2 - 8 to 14 inches: loam
H3 - 14 to 60 inches: loam
Properties and qualities
Slope: 6 to 12 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Medium
Capacity of the most limiting layer to transmit water (Ksat):
Moderately high to high (0.20 to 2.00 in/hr)
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 9.5 inches)
Interpretive groups
Land capability classification (irrigated): 4e
Land capability classification (nonirrigated): 4e
USDA Natural Resources Web Soil Survey 3/30/2020
onili Conservation Service National Cooperative Soil Survey Page 1 of 2
Map Unit Description: Yamo loam, 6 to 12 percent slopes —Aspen -Gypsum Area, Colorado,
Parts of Eagle, Garfield, and Pitkin Counties
Hydrologic Soil Group: B
Ecological site: Rolling Loam (R048AY298C0)
Other vegetative classification: Rolling Loam (null_60)
Hydric soil rating: No
Minor Components
Other soils
Percent of map unit: 20 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 10, Sep 13, 2019
USDA Natural Resources Web Soil Survey 3/30/2020
Conservation Service National Cooperative Soil Survey Page 2 of 2
Map Unit Description: Yamo loam, 1 to 6 percent slopes--Aspen-Gypsum Area, Colorado,
Parts of Eagle, Garfield, and Pitkin Counties
Aspen -Gypsum Area, Colorado, Parts of Eagle,
Garfield, and Pitkin Counties
114—Yamo loam, 1 to 6 percent slopes
Map Unit Setting
National map unit symbol: jq4q
Elevation: 6,200 to 7,500 feet
Mean annual precipitation: 10 to 14 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
Yamo and similar soils: 80 percent
Minor components: 20 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Yamo
Setting
Landform: Mountains, fans
Landform position (three-dimensional): Lower third of
mountainflank
Down -slope shape: Linear
Across -slope shape: Linear
Parent material: Colluvium derived from sandstone and/or
colluvium derived from shale and/or colluvium derived from
gypsum
Typical profile
H1 - 0 to 8 inches: loam
H2 - 8 to 14 inches: loam
H3 - 14 to 60 inches: loam
Properties and qualities
Slope: 1 to 6 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Runoff class: Low
Capacity of the most limiting layer to transmit water (Ksat):
Moderately high to high (0.20 to 2.00 in/hr)
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 9.5 inches)
Interpretive groups
Land capability classification (irrigated): 4e
Land capability classification (nonirrigated): 4e
USDA Natural Resources Web Soil Survey 3/30/2020
wool Conservation Service National Cooperative Soil Survey Page 1 of 2
Map Unit Description: Yamo loam, 1 to 6 percent slopes —Aspen -Gypsum Area, Colorado,
Parts of Eagle, Garfield, and Pitkin Counties
Hydrologic Soil Group: B
Ecological site: Rolling Loam (R048AY298C0)
Other vegetative classification: Rolling Loam (null_60)
Hydric soil rating: No
Minor Components
Other soils
Percent of map unit: 20 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 10, Sep 13, 2019
USDA Natural Resources Web Soil Survey 3/30/2020
21111 Conservation Service National Cooperative Soil Survey 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. ASFE/the 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 of the structure
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 limitations imposed by the client. To
help avoid costly problems, ask your geotechnical
engineer to evaluate how factors that change
subsequent to the date of the report may affect the
report's 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
report's development have changed.
A REPORT'S 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
discerned only during earthwork, you should retain
your geo- technical engineer to observe actual
conditions and to finalize recommendations. Only
the geotechnical engineer who prepared the report
is fully familiar with the background information
needed to determine whether or not the reports
recommendations are valid and whether or not the
contractor is abiding by applicable
recommendations. The geotechnical engineer who
developed your report cannot assume
responsibility or liability for the adequacy of the
report's 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 tests are advisable before construction
starts. Note, too, that additional tests may be
required when subsurface conditions 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 originally contemplated 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 those applied in geotechnical 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
your geotechnical consultant 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. To help avoid misinterpretations, retain
your geotechnical engineer to work with other
project design professionals who are affected by
the geotechnical report. Have your geotechnical
engineer 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
concerns, 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 report's
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 access 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 RESPONSIBILITY CLAUSES CLOSELY
Because geotechnical engineering is based
extensively on judgment and opinion, it is far Tess
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 transfer geotechnical 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 learn
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
Foundation Engineering
Rock Mechanics
Earthquake Engineering
Geophysics
Retaining Wall Design
Geostrructural Design
Pavement Design
Drainage Evaluations
Groundwater Studies
Environmental Assets
Building Assessments
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