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SOILS AND FOUNDATION INVESTIGATION
ADDITION TO 36 UTE PLACE
ASPEN, COLORADO
DEC 0 1 2005
AbrtI
BUILDING DEPARTMENT
Prepared For:
ZONE 4 ARCHITECTURE
P.O. Box 2508
Aspen, CO 81612
Attention: Mr. Keith Howie
Project No. GS04654-120
November 22, 2005
Received
234 Center Drive I Glenwood Springs, Colorado 81601
2/27/17
Telephone: 970-945-2809 Fax: 970-945-7411
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TABLE OF CONTENTS
SCOPE 1
SUMMARY OF CONCLUSIONS 1
SITE CONDITIONS 1
PROPOSED CONSTRUCTION 2
SUBSURFACE CONDITIONS 2
SITE EARTHWORK 3
Excavations 3
Structural Fill 4
Backfill 4
FOUNDATION 4
FLOOR SYSTEM AND SLABS-ON-GRADE 5
BELOW-GRADE CONSTRUCTION 6
SUBSURFACE DRAINAGE 6
SURFACE DRAINAGE 7
LIMITATIONS 8
FIGURE 1 -APPROXIMATE LOCATION OF EXPLORATORY PIT
FIGURE 2 —SUMMARY LOG OF EXPLORATORY PIT
FIGURE 3 — EXTERIOR FOUNDATION WALL DRAIN
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SCOPE
This report presents the results of our soils and foundation investigation for
the addition to 36 Ute Place in Aspen, Colorado. We conducted this investigation to
evaluate the subsurface conditions at the site and provide geotechnical
recommendations for the planned construction. Our report was prepared from data
developed from our field exploration, laboratory testing, engineering analysis, and
from our experience with similar conditions. The recommendations contained in the
report were developed based on the currently planned construction. We should be
informed if actual construction will differ significantly from the descriptions herein. A
summary of our conclusions is presented below.
SUMMARY OF CONCLUSIONS
1. Subsurface conditions encountered in our exploratory pit consisted of
about 2 feet of sandy clay "topsoil" underlain by clayey to silty gravel,
cobbles and boulders to the maximum explored depth of 6 feet below
existing ground surface.Ground water was not found in the exploratory
pit
2. We recommend constructing the addition on footing foundations
supported by the undisturbed, natural gravel soil. Design and
construction criteria for footings are presented in the report.
3. We judge potential differential settlement of slab-on-grade construction
supported by the undisturbed, natural gravel will be low. Additional
discussion is in the report.
4. Surface drainage should be designed to provide for rapid removal of
surface water away from the building. A foundation drain should be
installed around below-grade areas.
SITE CONDITIONS
The site is located at 36 Ute Place near the base of Aspen Mountain in Aspen,
Colorado. Single-family residences are south and east of the subject lot. The Ute
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Cemetery is to the southeast. The existing residence at 36 Ute Place is a two-story,
wood-frame building with an attached garage at the east side. A walkout basement is
below most of the building. A crawl space is below the east part of the main level
fifloor. The garage floor is a slab-on-grade near the main floor elevation. A patio and
landscaping are in the area of the planned addition.
a
_ Interior finish material and drywall in the building had been stripped as part of
remodeling at the time of our site visit. The building is constructed on footing
foundations. Foundation walls are constructed with concrete masonry units. Slab-
on-grade floors are in the basement and garage. Our observations indicate the
foundations, foundation walls, and slabs-on-grade have performed well. Wet
conditions are present in the south part of the crawl space. The moisture appears to
be due to seepage of exterior surface runoff.
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PLANNED CONSTRUCTION
Remodeling of the existing residence was in progress at the time of our
_ investigation. A two-story,wood-frame addition is planned adjacent to the southeast
part of the building. The main level of the addition will match the main level of the
existing residence. Footing foundations are planned for the addition. Bottom of
footings are planned about 4 feet below existing ground surface. We were informed
that the main floor of the addition would be structurally supported with a crawl space
- below. If actual construction will differ significantly from the descriptions above,we !.
should be informed so that we can check that our recommendations are appropriate.
SUBSURFACE CONDITIONS
Subsurface conditions in the area of the planned addition were investigated by
observing excavation of an exploratory pit(TP-1) at the approximate location shown
on Figure 1. Exploratory excavation operations were directed by our geotechnical
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engineer:.who logged the soils encountered in the borings and obtained samples for
:' testing in our laboratory. Graphic logs of the soils found...i,n,,our.exploratory borings
x
shown 0 n Fi ure2.
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encountered in o : ted •
of about 2
Subsurface conditionsurexplorato't `'pit'corisis
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feet of sandy clay"topsoil" underlain by clayey to:silty:::g:ra•vel.,:cobbles:and boulders •
to the maximum explored depth of 6 feet below:::existing:.:ground surface. Our •
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observations during exploratory excavation indicated:the.gravel:;was:.dense. Ground
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water.was not encountered in the exploratory pit.
EARTHWORK
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We anticipate excavations for foundatio site can be
accomplished usingconventional, heav duty excavation a ui ment .;Care must be
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:' ;:::• taken to avoid undermining the existing building. Excavation sides wilt. need to be
' sloped or braced to meet local, state and federal safety regulations We believe the
.:.:::.. natural gravel soil will classify as a Type C:soil:based on O.SHA-standards governing
excavations. Temporary slopes deeper than5.:feetshould.be.no steeperthan 1.5 to 1
(horizontal to vertical) in Type C soils. ,The:•.•contractor should identify the soils
encountered in excavations and refer to:OSHA standards to;;deterni:ne appropriate
slopes.
:
• We do not anticipate excavations for foundations or uti:lf;ities will penetrate the
•ground water table. However, excavation:s.:shou.ld:.beoped ta:::a.;::positive gravity
:. outfall or to a temporary sump where water from;;preci ptation canbe::removed by
excavations'should be-slog ed as,•much as
pumping. Ground surfaces surrounding,. �.,,:.....:...... �i
o the excavations:,:::>::; <::; _ :':::;:..
practical to direct runoff away fromgi,,, ,,:.,..:,:,,,, ..:: :'ry'i: ;�:.. •
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Structural Fill
4
Structural fill may also be required below the planned patio slabs. Structural
fill can consist of the on-site gravel soils provided they are free of rocks larger than 3-
inches in diameter, organics and debris. If import soils are desired for use as
structural fill,a sample should be submitted to our office for approval prior to hauling.
We suggest an AASHTO Class 6 aggregate base course or similar soil. Structural fill
should be placed in loose lifts of 10 inches thick or less, moisture-treated to within 2
percent of optimum moisture content, and compacted to at least 98 percent of
1 standard Proctor(ASTM D 698) maximum dry density. Our representative should be
1
called to check the density and moisture content of structural fill.
Backfill
Proper placement and compaction of backfill adjacent to foundation walls is 0
important to reduce infiltration of surface water and consolidation of backfill soil.
Backfilf should consist of the on-site soils or similar soils free of organics,debris and
rocks larger than 6 inches in diameter. Backfill should be placed in loose lifts of 10
inches thick or less,moisture-treated to within 2 percent of optimum moisture content
and compacted to at least 95 percent of standard Proctor(ASTM D 698)maximum dry
density. We recommend that density and moisture content of backfill be checked
_ during placement.
FOUNDATION
We recommend constructing the addition on footing foundations supported by
the undisturbed, natural gravel soil. Our representative should observe the completed
- foundation excavation to confirm that the exposed soils are as anticipated and
suitable for support of the designed footings, We expect footings designed
according to the criteria below will experience maximum total settlements of about 1
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inch. This settlement will be mostly differential with respect to the existing building.
Footings should be designed and constructed according to the criteria below.
1
1
1. The footing foundations should be supported by the undisturbed,
natural gravel soil. Soils loosened during the forming process for the
footings should be removed or re-compacted prior to placing concrete
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2. Footings should be designed for a maximum soil bearing pressure of
- 4,000 psf.
5
3. 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.
1
4. 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. 1
1
1
5. The soils under exterior footings should be protected from freezing.We
recommend the bottom of footings be constructed at a depth of at least
48 inches below finished exterior grades. The Aspen building
11 department should be consulted to verify the required frost protection
depth.
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FLOOR SYSTEM AND SLABS-ON-GRADE
4
We understand that no new interior slabs-on-grade are planned for the project.
A new patio will be constructed adjacent to the addition. Based on our field and
laboratory test data and our experience,we judge slab-on-grade construction can be
supported by the undisturbed, natural gravel with low risk of differential movement
and associated damage. Structural fill below the patio slab should be placed and
compacted as outlined in the Structural Fill section.
Exterior patio slabs should be isolated from the building. These slabs should
r be well reinforced to function as independent units. Frequent control joints should be
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provided, in accordance with American Concrete Institute(ACI) recommendations, to
reduce problems associated with shrinkage and curling.
BELOW-GRADE CONSTRUCTION
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 which 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 can
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.
We recommend design of below-grade walls using an equivalent fluid density
of at least 45 pcf for this site. Backfill placed adjacent to foundation wall exteriors
should be in accordance with the recommendations in the Backfill section.The above
equivalent density does not include allowances for sloping backfill, surcharges or
hydrostatic pressures. The recommended equivalent density assumes deflection;
some minor cracking of walls may occur. If very little wall deflection is desired, a
higher equivalent fluid density may be appropriate for design.
SUBSURFACE DRAINAGE
Water from precipitation, snow melt and surface irrigation of landscaping
frequently flows through relatively permeable backfill placed adjacent to a building
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and collects on the surface of relatively undisturbed soils at the bottom of the
excavation. This can cause wetting of foundation soils, hydrostatic pressures on
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foundation walls, and moist conditions in below-grade areas after construction. To•
mitigate these concerns, we recommend provision of a foundation drain around
below-grade areas.
The foundation drain should consist of a 4-inch diameter, perforated or slotted
PVC pipe encased in free draining gravel. The drain should lead to a positive gravity
outfall or to a sump pit where water can be removed by pumping. A typical
foundation drain detail is shown on Figure 3.
Crawl spaces should be provided with ventilation to maintain acceptable
humidity levels. It may be appropriate to install a ventilation system that is controlled
by a humidistat.
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SURFACE DRAINAGE 1
II
Surface drainage is critical to the performance of foundations, floor slabs and
concrete flatwork. We recommend the following precautions be observed: Ic
1. The ground surface surrounding the exterior of the building should be
sloped to convey surface water away from the building. In landscaped
areas, we recommend providing a slope of at least 6 inches in the first
5 feet away from the building.
2. Backfill adjacent to foundation wall exteriors should be moistened to
within 2 percent of optimum moisture content and compacted to at
least 95 percent of standard Proctor (ASTM D 698) maximum dry
density. 1
3. The building should be provided with gutters and downspouts. Roof
downspouts and drains should discharge well beyond the limits of all
backfill. Splash blocks and downspout extensions should be provided
at all discharge points. Water from roof and surface runoff should not
be introduced to the foundation drain system.
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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 or other landscaping requiring
comparatively large amounts of irrigation should not be located within
5 feet of the foundation. Sprinklers should be at least 5 feet from
building foundations and directed away from the building. Irrigation
should be limited to the minimum amount sufficient to maintain
vegetation; the application of additional water will increase the
likelihood of slab and foundation movements.
5. Impervious plastic membranes should not be used to cover the ground
surface immediately surrounding the buildings. 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.
LIMITATIONS
Our exploratory pit was located to obtain a reasonably accurate picture of the
subsurface. Variations in the subsurface conditions not indicated by the exploratory
pit will occur. Our representative should be called to observe the completed
foundation excavation to ensure that the subsoils are as anticipated from our field
investigation.
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 other warranty, express or
implied, is made. If we can be of further service or if you have questions regarding
this report, please call.
CTL I THOMPSON, INC.
es D. Kellogg, P.E.
Project Engineer
°=, 11 )220
JDK:cd
(5 copies sent)
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Approximate
Location of
Exploratory
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LEGEND: NOTES:
Sandy clay "topsoil", very 1. Exploratory pit was excavated
moist, dark brown. with a mini trackhoe on
November 21, 2005. The pit was
backfilled immediately after
excavation operations were
completed.
Gravel, cobbles, boulders,
clayey to silty matrix, dense, 2. No free ground water was found
moist, brown, gray. (GC—GM) in the exploratory pit at the time
i
of excavation.
3. Location of exploratory pit is
approximate.
4. This exploratory pit is subject to
the explanations, limitations and }'
conclusions as contained in this
report.
SUMMARY LOG OF EXPLORATORY PIT
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•
. •
___
./ .., -
rSLOPE ••
PER REPORT
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........ ..... PROVIDE PVC SHEETING GLUED
BELOW GRADE WALL -_ -- -_ TO FOUNDATION WALL TO REDUCE
----•----...--__-_-_-_-.- MOISTURE PENETRATION.
SLOPE :_._ .__::--_
PER _. -....-.-.__._.-::
OSHA BACKFILL _ _ -
(COMPOSITION AND : _ REINFORCED STEEL
COMPACTION PER REPORT) -- __- _ _ PER STRUCTURAL
DRAWINGS
COVER GRAVEL WITH =: =-x_-::-:_=._- CRAWL SPACE--
ENCASE PIPE IN WASHED FILTER FABRIC
CONCRETE AGGREGATE (ASTM --:_-::=_ = -_-_--
----------------
C33, NO. 57 OR NO. 67) ::::: _::::_:-
EXTEND GRAVE TO AT LEAST
1/2 HEIGHT OF FOOTING. E........._____________.„
_ __ _ _ _ f
SLOPE TO DRAW 2" MINIMUM
8" MINIMUM BOTTOM OF EXCAVATION
OR BEYOND 1:1
SLOPE FROM BOTTOM
OF FOOTING.
(WHICHEVER IS GREATER)
NOTE:
DRAIN SHOULD BE AT LEAST 2 INCHES
4-INCH DIAMETER PERFORATED BELOW BOTTOM OF FOOTING AT THE
DRAIN PIPE. THE PIPE SHOULD HIGHEST POINT AND SLOPE DOWNWARD
BE PLACED IN A TRENCH WITH A TO A POSITIVE GRAVITY OUTLET OR TO
SLOPE RANGE BETWEEN 1/8 INCH A SUMP WHERE WATER CAN BE REMOVED
AND 1/4 INCH DROP PER FOOT BY PUMPING.
OF DRAIN.
Exterior
Foundation
0
N Wall Drain
Project No. GS04654-120 Fig. 3
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