HomeMy WebLinkAboutSoils report 12.05.2012CTLITHOMPSON
SOILS AND FOUNDATION INVESTIGATION
LOTS 29 AND 30, ROARING FORK MESA
ASPEN GLEN
GARFIELD COUNTY, COLORADO
Prepared For:
PAUL GOLDSTEIN
5418 Oak Canopy Way
Ft. Lauderdale, FL 33312
Project No. GS05714-120
December 5, 2012
TABLE OF CONTENTS
SCOPE 1
SUMMARY OF CONCLUSIONS 1
SITE CONDITIONS 2
PROPOSED CONSTRUCTION 3
SUBSURFACE CONDITIONS 3
SITE GEOLOGY 4
GEOLOGIC HAZARDS 4
SITE EARTHWORK 6
Structural Fill 6
BACKFILL COMPACTION 7
FOUNDATION 8
Post -Tensioned Slab -on -Grade 8
Mat Foundation 10
Footings on Structural Fill 10
FLOOR SYSTEM AND SLABS -ON -GRADE 11
BELOW -GRADE CONSTRUCTION 12
SUBSURFACE DRAINAGE 13
SURFACE DRAINAGE 13
CONCRETE 14
CONSTRUCTION OBSERVATIONS 15
GEOTECHNICAL RISK 15
LIMITATIONS 16
FIGURE 1 — VICINITY MAP
FIGURE 2 - LOCATIONS OF EXPLORATORY BORINGS AND PITS
FIGURES 3 AND 4 — SUMMARY LOGS OF EXPLORATORY BORINGS AND PITS
FIGURE 5 — SWELL -CONSOLIDATION TEST RESULTS
FIGURE 6 — EXTERIOR FOUNDATION WALL DRAIN DETAILS
TABLE I — SUMMARY OF LABORATORY TESTING
PAUL GOLDSTEIN
LOTS 29 & 39, ROARING FORK MESA
PROJECT NO. GS05714.120
S:1GS05714.000112042. Reports10505714 120 R1.doc
SCOPE
This report presents the results of our soils and foundation investigation for
the proposed residence on Lots 29 and 30, Roaring Fork Mesa in Aspen Glen in
Garfield County, Colorado. We conducted this investigation to evaluate subsurface
conditions at the site and provide geotechnical engineering recommendations for the
proposed construction. We previously conducted a soils and foundation
investigation on Lot 29 (CTL Project No. GS05063-120, dated September 12, 2007).
Our report was prepared from data developed during our field exploration and a
previous investigation on Lot 29, engineering analysis, and our experience with
similar conditions. This report includes a description of the subsurface conditions
observed in our exploratory borings and pits and presents geotechnical engineering
recommendations for design and construction of the foundation, floor system, below -
grade wails, drain system, and details influenced by the subsoils. Recommendations
contained in this report were developed based on our understanding of the planned
construction. If plans differ significantly from the descriptions contained in the
report, we should be informed so that we can provide geotechnical engineering input
and check that our recommendations and design criteria are appropriate. A summary
of our conclusions is presented below.
SUMMARY OF CONCLUSIONS
1. Subsurface conditions encountered in our exploratory borings and pits
varied significantly. Subsurface conditions encountered in our
exploratory borings and pits consisted of about 0.5 to 1 foot of sandy
clay "topsoil" and silty sand or silty to clean gravel to the total explored
depth of 25 feet. The silty sand was encountered from about 3 to 9.5
feet in TP -1 and 1 to 4 feet in TP -2. The silty sand was encountered from
about 0.5 to 4 feet in TH-3 and 8 to 12 feet and 18 to 25 feet in TH-2.
Practical auger refusal occurred at multiple depths in TH-1 and TH-3.
Foundation and floor construction needs to consider the non-uniform
soils at the site. Free ground water was not observed in the
exploratory pits at the time of excavation or the borings at the time of
drilling.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714-120
S:1GS05714.000112012. ReportaGS05714 120 R1.doc
1
2. Differential settlement may occur if foundations are supported by the
different types of soils found on the lots. We recommend
subexcavation and replacement with structural fill to a depth of at least
5 feet below footings and replacement with structural fill. The potential
for sinkhole formation exists on this lot. We judge that the risk to
structures from sinkhole formation is low to moderate on this lot. A
positive foundation alternative on this lot to reduce the potential for
damage to the residence if a sinkhole forms is a structural mat (raft)
foundation or a post -tensioned slab -on -grade foundation supported on
at least 3 feet of structural fill or the natural gravel. A micropile
foundation system Is also a positive alternative. These types of
foundations are also less susceptible to damage from differential
movement. Design and construction criteria for foundations are
presented in the report.
3. We judge potential differential movement of slabs -on -grade supported
by the undisturbed, natural gravel will be low. We recommend removal
of sand or clay soils to a depth of at least 3 feet below slabs -on -grade
and replacement with granular structural fill. Additional discussion is in
the report.
4. It is critical that surface drainage be designed to provide for rapid
removal of surface water away from the residence. Foundation wall
drains should be provided around below -grade areas of the residence.
SITE CONDITIONS
Aspen Glen is located west of Highway 82 between Glenwood Springs and
Carbondale in Garfield County, Colorado (see Figure 1). Roaring Fork Mesa is located
near the center of the development northeast of County Road 109. Lots 29 and 30 are
east of Royal Coachman (see Figure 2). A drainage that was dry at the time of our
investigation is north of the lot. The Aspen Glen golf course driving range is to the
north and residential lots are to the east and south. Ground surface on the Tots drop
down to the north at grades of about 5 percent. Vegetation on the lot consists of
sparse grass and weeds.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714-120
S:4505714.000112012, Repor1slG505714 120 R1.d00
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PROPOSED CONSTRUCTION
We expect the residence will be a one or two-story, wood -frame building with
an attached garage. A crawl -space below the residence may be provided in living
areas. Slab -on -grade floors are likely the desired floor system in the garage. We
expect, maximum foundation excavation depths will be about 3 to 5 feet. Completed
wall backfill depth may be slightly more than excavation depth as final grades are
adjusted for drainage. Foundation loads are expected to vary between 1,000 and 3,000
pounds per linear foot of foundation wall with maximum interior column loads of 30
kips. If construction will differ significantly from the descriptions above, we should
be informed so that we can adjust our recommendations and design criteria, if
necessary.
SUBSURFACE CONDITIONS
Subsurface conditions encountered in our exploratory borings and pits varied
significantly. Subsurface conditions encountered in our exploratory borings and pits
consisted of about 0.5 to 1 foot of sandy clay "topsoil" and silty sand or silty to clean
gravel to the total explored depth of 25 feet. The silty sand was encountered from
about 3 to 9.5 feet in TP -1 and 1 to 4 feet in TP -2. The silty sand was encountered from
about 0.5 to 4 feet in TH-3 and 8 to 12 feet and 18 to 25 feet in TH-2. Practical auger
refusal occurred at multiple depths in TH-1 and TH-3. Foundation and floor
construction needs to consider the non-uniform soils at the site. Free ground water
was not observed in the exploratory pits at the time of excavation or the borings at
the time of drilling.
Subsurface conditions encountered in the borings and pits were logged by our
field representative who obtained samples of the soils encountered in our exploratory
borings and pits. Graphic logs of the soils observed in the exploratory borings and
pits are shown on Figures 3 and 4. Our observations during excavation indicated the
sand was loose to medium dense and the gravel was dense to very dense. The
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714.120
S:5GS05714AQ9112912, IR poAs1GS05714 120 R1.doc
3
borings and pits were backfilled immediately after drilling and excavation operations
were completed.
Samples obtained in the field were returned to our laboratory where field
classifications were checked and samples were selected for pertinent testing. Two
samples of the gravel contained 8 and 22 percent silt and clay sized particles (passing
the No. 200 sieve). Gradation test results exclude cobbles and boulders. Samples of
the silty sand contained 40 to 45 percent silt and clay sized particles and exhibited a
liquid limit 19 and a plasticity index of 2. A sample of the silty sand selected for swell -
consolidation testing exhibited 2.2 percent compression when wetted under an
applied pressure of 1,000 psf. Swell -consolidation test results are shown on Figure 5.
Laboratory test results are summarized on Table I.
SITE GEOLOGY
The geology of the site was evaluated using our in-house collection of
geologic maps (Geologic Map of the Cattle Creek Quadrangle, Garfield County,
Colorado by Kirkham et. al., 1996). We interpret the surficial soils of the site as
younger debris flow and colluvium deposits underlain by the Eagle Valley Formation.
We did not encounter bedrock in our borings and pits. The subsurface conditions
observed in our borings and pits are consistent with the mapping we reviewed.
GEOLOGIC HAZARDS
Colorado is a challenging location to practice geotechnical engineering. The
climate is relatively dry and the near -surface soils are typically dry and relatively stiff.
These soils and related sedimentary bedrock formations tend to react to changes in
moisture conditions. Some of the soils swell as they increase in moisture and are
called expansive soils. Other soils can settle significantly upon wetting and are
referred to as collapsing soils. Most of the land available for development east of the
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT N0. GS05714-120
5010505714.000112012. Roports1GS05714 120 111.doe
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Front Range is underlain by expansive clay or claystone bedrock near the surface.
The soils that exhibit collapse potential are more common west of the continental
divide; however, both types of soils occur all over the state.
Covering the ground with houses, streets, driveways, patios, etc., coupled with
lawn Irrigation and changing drainage patterns, leads to an increase in subsurface
moisture conditions. As a result, some soil movement is inevitable. It is critical that
all recommendations in this report are followed to increase the chances that the
foundations and slabs -on -grade will perform satisfactorily. After construction, owners
must assume responsibility for maintaining the structure and use appropriate
practices regarding drainage and landscaping.
Some increase in subsurface moisture must be assumed due to the effects of
site development. We compared moisture content and dry density from a sample
from the site to collapse potential based on a rating system described in "Engineering
Geology 14, Collapsible Soils in Colorado". Based on the rating system, the soils
exhibit moderate to high collapse potential. A sample tested in our laboratory
exhibited moderate collapse when wetted under loads of 1,000 psf. Based on our
experience in the area, laboratory testing and published data, we consider the upper
soils at this site to have collapse potential. Engineered design of foundations, slabs -
on -grade, pavements and surface drainage can mitigate the effects of collapse -prone
soils.
Lots 29 and 30 of Roaring Fork Mesa are located on a young debris -flow
alluvial fan over Eagle Valley bedrock. The Colorado Geologic Survey has mapped
sinkhole, subsidence and soli -collapse features and locations in the area near this lot
(Collapsible Soils and Evaporite Karst Hazards Map of the Roaring Fork River
Corridor, Garfield, Eagle and Pitkin Counties, Colorado by Jonathan L. White, 2002).
We did not observe obvious visual evidence of sinkhole/subsidence formations in the
immediate area surrounding the lot; however, we judge the lot has a low to moderate
potential for sinkhole formation or collapse of the soils due to wetting after
construction.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714-120
S: SGS05714.000%1201.2. R.por1 1GS05714 120 R1.doc
5
SITE EARTHWORK
Based on information from our exploratory borings and pits, we anticipate that
the excavation for the proposed residence will be through sand and gravel soils. We
anticipate excavation of the soils can be accomplished using conventional, heavy
duty excavating equipment. Sides of excavations need to be sloped to meet local,
state and federal safety regulations. The silty sand soils may classify as a Type B soil
based on OSHA standards governing excavation; the natural gravel will likely classify
as Type C soil. Temporary slopes deeper than 4 feet that are not retained should be
no steeper than 1 to 1 (horizontal to vertical) in Type B soils or 1.5 to 1 in Type C soils.
Excavations into the gravel may encounter boulders and significant amounts of
cobbles. Contractors should identify soils encountered and ensure that applicable
standards are met. Contractors are responsible for site safety and maintenance of the
work site.
Free ground water was not observed in the exploratory borings and pits during
exploratory operations. We do not anticipate excavations for foundations or utilities
will penetrate ground water, however, excavations should be sloped to a gravity
discharge or to a temporary sump where water can be removed by pumping, if
necessary. We should be contacted if ground water is encountered to provide
additional permanent subsurface drain recommendations.
Structural Fill
Excavations for the residence will likely encounter sand and gravel soils at
foundation or slab elevations. Differential settlement of the residence is likely if the
foundations are supported on different soils. We recommend the sand soils be
removed from below the building footprint. As a minimum, we recommend removal of
the sand to a depth of at least 3 feet below mat or post -tensioned slab -on -grade
foundations and slab -on -grade and replacement with densely compacted, granular
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714.120
S:\GS05714.0001120V2. Raparls1GS05714 120 R1.dac
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structural fill. We recommend subexcavation of the sand and gravel to a depth of 5
feet below footings and replacement with structural fill. Areas which will receive fill
should be stripped of vegetation, organic soils and debris. We recommend structural
fill consisting of imported COOT Class 6 aggregate base course or similar soil.
Structural fill should be placed in loose lifts of 10 inches thick or less and
moisture conditioned to within 2 percent of optimum moisture content. Structural fill
should be compacted to 100 percent of ASTM D 698 maximum dry density. Moisture
content and density of structural fill should be checked by a representative of our firm
during placement.
BACKFILL COMPACTION
We recommend foundation wall backfill be placed and compacted to reduce
settlement. However, compaction of the backfill soils adjacent to concrete walls may
result in cracking of the wall. The potential for cracking can vary widely based on
many factors including the degree of compaction achieved, the weight and type of
compaction equipment utilized, the structural design of the wall, the strength of the
concrete at the time of backfill compaction, and the presence of temporary or
permanent bracing.
Our experience indicates wall backfill soils that have been moisture
conditioned to within 2 percent of optimum moisture content and compacted to at
least 90 percent of maximum standard Proctor dry density (ASTM D 698) are typically
sufficiently dense to reduce settlement. Compacting the backfill soils to higher
density increases the risk of cracking the concrete wail. Particles in excess of 3
inches in diameter should be excluded from the backfill soils. Frost or frozen soils
should not be used for backfill.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS95714.120
5:56505714.0 0 01120l2. ReporlslG005714 120 111.doc
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FOUNDATION
Our exploratory borings and pits indicate that natural gravel with cobbles and
boulders and sand are present at anticipated foundation elevations for the proposed
residence. The silty sand soils have the potential to collapse when wetted. The
natural soils on this site are underlain by Eagle Valley Formation bedrock. The
potential for subsurface voids and related sinkholes exists on the site. We did not
observe evidence of sinkholes on the site. We judge that the risk of foundation
damage from sinkholes on this site is low to moderate. Due to the variable soils,
geologic setting, and the risk of sinkhole formation, we recommend that the residence
be supported on a post -tensioned slab or mat (raft) foundation system. A post -
tensioned slab or mat foundation system may allow mitigation of distress from a
sinkhole prior to extensive structural damage. These foundations also reduce the
potential for building damages from differential movement. A micropile foundation
system is another positive alternative. We will provide recommendations for
micropiles, if requested. Footings supported on a minimum thickness of 5 feet of
granular structural fill are an option, if the owner is willing to accept the increased
risk of movement.
Our representative should be called to observe conditions exposed in the
completed foundation excavation to confirm that the exposed soils are as anticipated
and suitable for support of the foundation as designed. Our experience indicates that
maximum total settlement will be 1 inch and differential settlement about 3/4 inch for
footings constructed on structural fill. We would anticipate about one-half as much
movement for a post -tensioned slab or mat foundation. Recommended design and
construction criteria for post -tensioned slabs and a mat (raft) foundation are
presented below.
Post -Tensioned Slab -on -Grade
The post -tensioned, slab -on -grade foundation may be constructed on
the undisturbed, natural gravel soils. The silty sand should be removed
to a depth of at least 3 feet and replaced with structural fill. If soft or
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO, G905114-120
S:4GS05744..000\120\2. Roporls5GR05714 120 R1.dos
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loose soils are exposed in excavations, the soft soils should be
removed and recompacted to at least 100 percent of standard Proctor
maximum dry density (ASTM D 698) within 2 percent of optimum
moisture content prior to placing concrete.
2. The foundations should be designed for a maximum allowable soil
pressure of 1,500 psf.
3. Based on our subsurface information and assuming a depth of 3 feet
for stiffening beams, we estimate the total settlement in the center of
the building may be 3/4 inch. Our experience indicates differential
settlement between the center and the edges may be 0.5 inches. The
structural engineer should consider designing the slab to bridge voids
in the event a sinkhole forms.
4. We understand the PTI design method assumes the slab is somewhat
flexible. Some above -grade construction is not as flexible, such as
drywall and brick or stucco. We are aware of situations where minor
differential slab movement has caused distress in finish materials. One
way to enhance performance would be to place reinforcing steel in the
bottom of stiffening beams. The structural engineer should evaluate
the merits of this approach and other potential alternatives.
5. Soils may cave or slough during trench excavation for the stiffening
beams. Disturbed soils should be removed from trench bottoms prior
to placement of concrete. Formwork or other methods may be required
for proper stiffening beam installation.
6. Exterior stiffening beams must be protected from frost action.
Normally 36 inches of frost cover is assumed in the area. The Garfield
County Building Department should be consulted regarding required
frost protection depth.
7. For slab tensioning design, a coefficient of friction value of 0.75 or 1.0
can be assumed for slabs on a polyethylene sheeting or a sand layer,
respectively. A coefficient of friction of 1 should be used for slabs
supported on the natural soils.
8. A representative of our firm should observe the completed foundation
excavation. A representative of the structural engineer or our firm
should inspect the placement of the reinforcing tendons and
reinforcement prior to placing the slabs and beams.
9. Underslab plumbing should be pressure tested before the slab is
constructed.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714.120
S.1G505714.000112012. Reporjs1G505714 120 R 1.doc
9
Mat Foundation
1. The reinforced concrete mat foundation can be constructed on the
undisturbed gravel soils. Silty sand soil should be removed to a depth
of at least 3 feet and replaced with structural fill.
2. The mat foundation should be designed for a maximum allowable soil
pressure of 1,500 psf if constructed on the natural sand and gravel
soils.
3. Modulus of subgrade reaction (Ks) is normally used for mat foundation
design. The modulus of subgrade reaction is dependent upon the
compressibility of the foundation soils and the size (or effective loaded
area) of the foundation. If the entire mat foundation is uniformly loaded,
then a Ks value of 150 pci should be used for the natural sand and
gravel soils.
4. To resist lateral Toads, a coefficient of friction of 0.40 can be used for
concrete in contact with the natural sand and gravel soils. Lateral Toads
can be resolved by evaluating passive resistance using an equivalent
fluid density of 300 pcf for the natural soils, provided the backfill is
compacted and is not removed. A moist unit weight of 130 pcf can be
assumed for backfill soils. These values have not been factored;
appropriate factors of safety should be applied in design.
5. Soil beneath the foundation must be protected from freezing. We
recommend the bottom of the foundation be constructed at a depth of
at least 36 inches below finished exterior grades. The applicable
building department should be consulted regarding required frost
depths.
Footings on Structural Fill
1. The building can be supported by footing foundations on a minimum 5
foot thickness of densely compacted granular structural fill. The
structural fill should extend at least 3 feet horizontally from the bottom
of the footings. Soils loosened during the forming process for the
footings should be removed or re -compacted prior to placing concrete.
2. Footings on the structural fill can be sized using a maximum allowable
bearing pressure of 2,000 psf.
4. Continuous wall footings should have a minimum width of at least 16
inches. Foundations for isolated columns should have minimum
dimensions of 24 inches by 24 inches. Larger sizes may be required,
depending upon foundation loads.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO, GS05714-120
S 1GS05714.0001120'12. Reporls1GS05714 12D FR1.d0e
10
5. Grade beams and foundation walls should be well reinforced, top and
bottom, to span undisclosed loose or soft soil pockets. We
recommend reinforcement sufficient to span an unsupported distance
of at least 12 feet. Reinforcement should be designed by the structural
engineer.
6. The soils under exterior footings should be protected from freezing. We
recommend the bottom of footings be constructed at a depth of at least
36 inches below finished exterior grades. The Carbondale building
department should be consulted regarding required frost protection
depth.
FLOOR SYSTEM AND SLABS -ON -GRADE
If a mat foundation or post -tensioned slab is constructed, the foundation will
act as the floor slab. If a footing foundation on granular structural fill is chosen, a
slab -on -grade may be constructed in the garage area. Structural floors with a crawl
space below are a positive alternative from a geotechnical perspective. Based on our
laboratory test data and our experience, we judge slab -on -grade construction
supported by undisturbed, natural gravel or an at least 3 foot thickness of densely
compacted granular structural fill will have a low to moderate risk of differential
movement and associated damage. Structural fill placed to attain subgrade elevations
for the floor slab and exterior concrete flatwork should be in accordance with the
recommendations outlined in the Structural Fill section.
We recommend the following precautions for slab -on -grade construction at
this site. These precautions will not prevent movement from occurring; they tend to
reduce damage if slab movement occurs.
1. Slabs should be separated from exterior walls and interior bearing
members with slip joints which allow free vertical movement of the
slabs.
2. The use of underslab plumbing should be minimized. Underslab
plumbing should be pressure tested for leaks before the slabs are
constructed. Plumbing and utilities which pass through slabs should
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714-120
S:0GS05714. 000412042 Repe1ts1GS05714 120 R1.doc
11
be isolated from the slabs with sleeves and provided with flexible
couplings to slab supported appliances.
3. Exterior patio and porch slabs should be isolated from the building.
These slabs should be well -reinforced to function as independent units.
Movements of these slabs should not be transmitted to the building.
4. Frequent control joints should be provided, in accordance with
American Concrete Institute (ACI) recommendations, to reduce
problems associated with shrinkage and curling.
BELOW -GRADE CONSTRUCTION
We understand below -grade areas, with the exception of a crawl space, are not
planned. If constructed, foundation walls which extend below -grade should be
designed for lateral earth pressures where backfill is not present to about the same
extent on both sides of the wall. Many factors affect the values of the design lateral
earth pressure. These factors include, but are not limited to, the type, compaction,
slope and drainage of the backfill, and the rigidity of the wall against rotation and
deflection. For a very rigid wall where negligible or very little deflection will occur, an
"at -rest" lateral earth pressure should be used in design. For walls that can deflect or
rotate 0.5 to 1 percent of wall height (depending upon the backfill types), lower
"active" lateral earth pressures are appropriate. Our experience Indicates typical
basement walls in residences deflect or rotate slightly under normal design loads,
and that this deflection results in satisfactory wall performance. Thus, the earth
pressures on the walls will likely be between the "active" and "at -rest" conditions.
If the on-site soils are used as backfill, we recommend design of below -grade
walls using an equivalent fluid density of at least 50 pcf for this site. This equivalent
density does not include allowances for compaction energy, sloping backfill,
surcharges or hydrostatic pressures. Backfill should be placed in accordance with
the recommendations contained in the BACKFILL COMPACTION section.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714-120
S:5GS05714.000112012. Reports1G505714 120 R1.dac
12
SUBSURFACE DRAINAGE
Water from rain, snow melt and surface irrigation of lawns and landscaping
frequently flows through relatively permeable backfill placed adjacent to a residence
and collects on the surface of relatively impermeable soils occurring at the bottom of
the excavation. This can cause wetting of foundation soils, hydrostatic pressures on
below -grade walls, and wet or moist conditions in below -grade areas after
construction. We recommend provision of a foundation drain around below -grade
areas in the building. The drain should consist of a 4 -inch diameter, slotted PVC pipe
encased in free draining gravel. The drain should lead to a sump pit where water can
be removed by pumping. A typical foundation dram detail is presented on Figure 6.
SURFACE DRAINAGE
Surface drainage is critical to the performance of foundations, floor slabs and
concrete flatwork. Infiltration of water can cause sinkhole formation in Evaporite
bedrock and settlement of collapsible soils. Estimated movements in this report are
based on effective drainage for the life of the structure and cannot be relied upon if
effective drainage is not maintained. We recommend the following precautions be
observed during construction and maintained at all times after the residence is
completed:
1. The ground surface surrounding the exterior of the residence should
be sloped to drain away from the residence in all directions. We
recommend providing a slope of at least 6 inches in the first 5 feet
around the residence.
2. Backfill around the exterior of foundation walls should be placed as
described in the BACKFILL COMPACTION section. Increases in the
moisture content of the backfill soils after placement often results in
settlement. Settlement is most common adjacent to north facing walls.
Re -attaining proper slopes away from the residence may be necessary.
3. The residence should be provided with roof gutters and downspouts.
Roof downspouts and drains should discharge well beyond the limits
PAUL GQLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714-120
S[GS05714.000%12012. RepodeLG505714 120 R1.tiot
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of all backfill. Splash blocks and downspout extensions should be
provided at all discharge points.
4. Landscaping should be carefully designed to minimize irrigation.
Plants used near foundation walls should be limited to those with low
moisture requirements; irrigated grass should not be located within 5
feet of the foundation. Sprinklers should not discharge within 5 feet of
the foundation and should be directed away from the residence.
5. Impervious plastic membranes should not be used to cover the ground
surface immediately surrounding the residence. These membranes
tend to trap moisture and prevent normal evaporation from occurring.
Geotextile fabrics can be used to control weed growth and allow some
evaporation to occur.
CONCRETE
Concrete in contact with soil can be subject to sulfate attack. Our information
on nearby Tots in the Aspen Glen area indicates low sulfate concentrations. For low
levels of sulfate concentration, ACI 332-08 Code Requirements for Residential
Concrete indicates there are no special requirements for sulfate resistance. Do to
time constraints; sulfate testing was not complete at this writing. We will provide
revised recommendations if sulfate testing, when complete, indicates otherwise.
In our experience, superficial damage may occur to the exposed surfaces of
highly permeable concrete, even though sulfate levels are relatively low. To control
this risk and to resist freeze -thaw deterioration, the water-to-cementitious materials
ratio should not exceed 0.50 for concrete in contact with soils that are likely to stay
moist due to surface drainage or high water tables. Concrete should have a total air
content of 6% +1- 1.5%. We recommend all foundation walls and grade beams in
contact with the subsoils (including the inside and outside faces of garage and crawl
space grade beams) be damp -proofed.
PAUL GOLDSTEIN
LOTS 29 & 30, ROARING FORK MESA
PROJECT NO. GS05714.120
S \G50571,1 000112012. ReportO\G$05714 120 R1.doc
14
CONSTRUCTION OBSERVATIONS
This report has been prepared for the exclusive use of Mr. Paul Goldstein and
the design team for the purpose of providing geotechnical design and construction
criteria for the proposed project. The information, conclusions, and recommendations
presented herein are based upon the consideration of many factors including, but not
limited to, the type of structure proposed, the geologic setting, and the subsurface
conditions encountered. The conclusions and recommendations contained in the
report are not valid for use by others. Standards of practice change continuously in
the area of geotechnical engineering. The recommendations provided are appropriate
for about three years. If the proposed structure is not constructed within about three
years, we should be contacted to determine if we should update this report.
We recommend that CTL 1 Thompson, Inc. provide construction observation
services to allow us the opportunity to verify whether soil conditions are consistent
with those found during this investigation. If others perform these observations, they
must accept responsibility to judge whether the recommendations in this report are
appropriate.
GEOTECHNICAL RISK
The concept of risk is an important aspect of any geotechnical evaluation. The
primary reason for this is that the analytical methods used to develop geotechnical
recommendations do not comprise an exact science. The analytical tools which
geotechnical engineers use are generally empirical and must be tempered by
engineering judgment and experience. Therefore, the solutions or recommendations
presented in any geotechnical evaluation should not be considered risk-free and,
more importantly, are not a guarantee that the interaction between the soils and the
proposed structure will perform as desired or intended. What the engineering
recommendations presented in the preceding sections do constitute is our estimate,
based on the information generated during this and previous evaluations and our
PAUL GOLDSTEIN
LOTS 29 S 39, ROARING FORK MESA
PROJECT NO. GS05714.120
SAGSO5714.990112O\2. RapadslGS05714 12D 111.doe
15
experience in working with these conditions, of those measures that are necessary to
help the residence perform satisfactorily. The developer, builder, and future owners
must understand this concept of risk, as it is they who must decide what is an
acceptable level of risk for the proposed development of the site.
LIMITATIONS
The exploratory borings and pits on the lots provide a reasonably accurate
picture of subsurface conditions. Variations in the subsurface conditions not
indicated by the pits will occur. This investigation was not performed to identify
potential sink holes on the lot. We can perform an investigation to attempt to identify
sinkhole, if desired. A representative of our firm should be called to test structural fill
placement and to observe the completed foundation excavation to confirm that the
exposed soils are suitable for support of the footings as designed. Post -tensioned
slab installation should be inspected by a qualified inspector. We should observe and
test placement of fill.
This investigation was conducted in a manner consistent with that level of care
and skill ordinarily exercised by geotechnical engineers currently practicing under
similar conditions in the locality of this project. No warranty, express or implied, is
made. If we can be of further service in discussing the contents of this report, please
call.
CTL 1 THOMPSON, INC. Reviewed by:
Craig A. Burger, P.E.
Project Manager _
CAB:JM:cd
cc: Via email to mcstein@gate.net
PAUL GOLDSTEIN
LOTS 29 8 30, ROARING FORK MESA
PROJECT NO. GS05714.120
S'. 16505714.600\l20't2, Rep0rt3\GS05714 120 RI,doc
Sohn Mechling, P.E.
Branch Manager
16
��
SCALE:1'
PAUL GOLDSTEIN
LOTS 29 AND 30, ROARING FORK MEGA
Project No. GS05714-120 Flg. 1
Vicinity
Map
SCALE: 1' = 50'
OM I 1 I I ZM m M 1:ti
PAUL GOLDSTEIN
LOTS 29 AND 30, ROARING PORK MESA
ASPEN GLEN
Project No. GS05714-120
ROTE:
Locations of exploratory borings
and pits ars approximate.
Locations of
Exploratory
Borings and
Pits
Fig. 2
o.
Project No. GS05714—f 20
10
15
20
25
30
TH-1
0/13.
30/0
TH-2
15/12,
28/6
11/18
43/12
9/12
///J� 115/12
TH-3
TP -1 TP -2
35/16
Anticipated
Foundation
Elevatlon
SUMMARY LOGS OF EXPLORATORY BORINGS AND PITS
0
5
10
15
20
25
30
064 ui 144100
Fig. 3
LEGEND:
El Sandy clay "topsoil`, organics,
moist, brown, rust.
grg
Gravel, clean to silty. cobbles and
boulders, dense to very dense,
slightly moist, brown, nut. (CP -014)
Sand, silty, occasional gravel, loose
to medium dense, slightly moist to
moist, rust. brown. (SM)
Drive sample. The symbol 3D/13
Indicates that 30 blows of a 140
pound hammer falling 30 inches
were required to drive o 2.5 Inch
0.D. California sampler 3 inches.
Project No. GS05714-120
F
Drive sample. The symbol 15/12
Indicates that 15 blows of a 140
pound hammer falling 30 Inches
were required to drive a 2.0 Inch
0.D. standard sampler 12 inches.
indicates bulk sample.
Indicates hand drive sample.
lndlcates practical auger refusal.
Symbols above the bottom of
borings Indicates that boring location
was moved to advance auger
farther.
SUMMARY LOGS OF EXPLORATORY BORINGS AND PITS
NOTES:
1. Exploratory borings were drilled on
August 28, 2007 with 4—Inch
diameter. solid—stem auger and o
track—mounted drill rig. Exploratory
pits were excavated on December 4,
2012. Exploratory borings and pits
were backfilled immediately after
exploratory operations were
compteted.
2. Locations of exploratory borings and
pits are approximate.
3. No free ground water was found In
our exploratory borings or plts at
the time of exploratory operations.
4. These exploratory borings and pits
are subject to the explanations.
limitations and concluslons as
contained In this report.
Flg. 4
COMPRESSION % EXPANSION
-a
ADDITIONAL COMPRESSION UNDER
CONSTANT PRESSURE DUE TO WETTING
L1
10
1❑ 100
APPLIED PRESSURE - KSF
Sample of SAND, SILTY (SM) DRY UNIT WEIGHT= 101 PCF
From TP -2- AT 3.5 FEET MOISTURE CONTENT= 3.6 %
Paul Goldstein
Lots 29 A. 30 Roaring Fork Mesa, Aspen Glen
PROJECT NO. GS05714-120
S.1GS05714.000112016. CaIcs1GS05714-1205WELL.xIs
Swell Consolidation
Test Results
FIG. 5
SLOPE
PER REPORT
BACKFILL
BELOW -GRADE WALL
STRUCTURAL FLOOR
SLOPE . ATTACH POLYETHYLENE
PER SHEETING TO FOUNDATION
OSHA WALL
COVER ENTIRE WIDTH OF
GRAVEL WITH NON -WOVEN
GEOTEXTILE FABRIC
(TENCATE MIRAFI 140N OR
EQUIVALENT). ROOFING
FELT IS AN ACCEPTABLE
ALTERNATIVE.
8' MIN. OR
BEYOND 1:1
SLOPE FROM BOTTOM
OF FOOTING (WHICHEVER
I5 GREATER)
4' MINIMUM
4 -INCH DIAMETER PERFORATED RIGID DRAIN
PIPE. THE PIPE SHOULD BE PLACED IN A
TRENCH WITH A SLOPE OF AT LEAST
1/8 -INCH DROP PER FOOT OF DRAIN.
CRAWL
SPACE OR
VOID
SEE NOTE 2
FOOTING OR PAD
ENCASE PIPE IN 1/2' TO 1-1/2' WASHED GRAVEL EXTEND
GRAVEL LATERALLY TO FOOTING AND AT LEAST 1/2 HEIGHT OF
FOOTING. FILL ENTIRE TRENCH WITH GRAVEL.
NOTES:
1) THE BOTTOM OF THE DRAIN SHOULD BE AT LEAST 4 INCHES BELOW BOTTOM OF
FOOTING AT THE HIGHEST' POINT AND SLOPE DOWNWARD TO A POSITIVE GRAVITY
OUTLET OR TO A SUMP WHERE WATER CAN BE REMOVED BY PUMPING.
2) TO HELP CONTROL THE HUMIDITY IN THE CRAWL SPACE, A MINIMUM 10 -MIL
POLYETHYLENE VAPOR RETARDER MAY BE PLACED OVER THE CRAWL SPACE
SOILS, AT THE BUILDER'S OPTION. THE RETARDER SHOULD BE ATTACHED TO
CONCRETE FOUNDATION ELEMENTS AND EXTEND UP FOUNDATION WALLS AT
LEAST 8 INCHES ABOVE TOP OF FOOTING. OVERLAP JOINTS 3 FEET AND SEAL
PAUL GOLDSTEIN
LOTS 2S AND 30, ROARING FORK MESA
Protect No. GS05714-120
Exterior
Foundation
Wall Drain
Flg. 6
PROJECT NO. GS05714.120
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
BORING
1 OR
PIT
I DEPTH
(FEET)
NATURAL
MOISTURE
(%)
NATURAL
DRY
DENSITY
(PCF)
SWELL'
(%)
ATTERBERG LIMITS
SOLUBLE
SULFATES
(%)
GRADATION TESTS
PASSING
NO. 200
SIEVE
(%)
SOIL CLASSIFICATION
LIQUID
LIMIT
(%)
PLASTICITY
INDEX
(%)
PERCENT
GRAVEL
(%)
PERCENT
SAND
(%)
TH-2
4
1.9
22
GRAVEL, SILTY (GM)
TH-2
9
7.6
19
2
45
SAND, SILTY (SM)
TH-2
14
2.2
8
GRAVEL, CLEAN TO SILTY (GP -GM)
TP -1
7-9
4.1
8
52
40
SAND, SILTY (SM)
TP -2
3.5
3.6
101
-2.2
SAND, SILTY(SM)
TP -2
2-4
3.9
13
47
40
SAND, SILTY (SM)
"Note: Swell due to wetting under an applied load of 1,000 psf. Negative values indicate compression.
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