HomeMy WebLinkAboutGeotechnical InvestigationCTLITHOMPSON
GEOTECHNICAL INVESTIGATION
VAUGHAN RESIDENCE ADDITION
1038 COUNTY ROAD 323
GARFIELD COUNTY, COLORADO
Prepared For:
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
1038 County Road 323
Rifle, CO 81650
Attention: Mr. Phil Vaughan
Job No. GS -4287
July 21, 2004
234 Center Drive 1 Glenwood Springs, Colorado 81601
Telephone: 970-945-2809 Fax: 970-945-7411
TABLE OF CONTENTS
SCOPE 1
SUMMARY OF CONCLUSIONS 1
SITE CONDITIONS 2
PROPOSED CONSTRUCTION 2
SUBSURFACE CONDITIONS 2
SITE EARTHWORK 3
Excavation 3
Structural Fill 4
Backfill 5
FOUNDATIONS 5
Footings on Natural Gravel 5
Footings on Structural Fill 6
FLOOR SYSTEM AND SLABS -ON -GRADE 7
BELOW -GRADE CONSTRUCTION 8
SURFACE DRAINAGE 8
LIMITATIONS 9
FIGURE 1 -APPROXIMATE LOCATIONS OF EXPLORATORY PITS
FIGURE 2 —SUMMARY LOGS OF EXPLORATORY PITS
FIGURE 3 -- SWELL CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
FIGURE 5— EXTERIOR FOUNDATION WALL DRAIN
TABLE I —SUMMARY OF LABORATORY TEST RESULTS
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL I T JOS NO. GS -4217
SCOPE
This report presents the results of our geotechnical investigation for the
proposed addition to the Vaughan Residence at 1038 County Road 323 in Garfield
County, Colorado. We conducted this investigation to evaluate subsurface conditions
at the site and provide foundation recommendations for the proposed construction.
Our report was prepared from data developed during observation of subsurface
conditions exposed in exploratory pits excavated at the site, engineering analysis and
our experience with similar conditions. This report includes a description of the
subsurface conditions observed in exploratory pits, and presents recommendations
for design criteria for the recommended foundation and floor system, and
geotechnical and construction criteria for 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 check that
our recommendations and design criteria are appropriate. A summary of our
conclusions is presented below.
SUMMARY OF CONCLUSIONS
1.. Subsurface conditions observed in the exploratory pits consisted of
about 2.5 and 6 feet of silty sandy clay underlain by clayey to silty
gravel with basalt cobbles and boulders to the total explored depth of
7.5 feet below existing ground surface. Free ground water was not
observed in the exploratory pits at the time of excavation.
2. The silty sandy clay soil at the site possesses potential for excessive
consolidation when wetted under load. To reduce potential for
differential movement between the addition and existing building, we
recommend constructing the addition on footings supported by the
natural gravel or densely compacted, granular, structural fill. Design
and construction criteria for footings are presented in the report.
3. The addition floor slab should be supported by the natural gravel or a
12 -inch thick mat of densely compacted, granular, structural fill.
Additional discussion is in the report.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL IT JOB No. GS -42117
1
4. Surface drainage should be designed to provide for rapid removal of
surface water away from the residence.
SITE CONDITIONS
The Vaughan Residence is located at 1038 County Road 323. The residence is
a one-story, wood -frame building with a basement. Basement walls are masonry
block. The basement floor is 7 to 8 feet below -grade. Our subsurface information
indicates that the natural gravel is present at foundation elevation for the residence.
The existing residence appears to have performed well. Lawn and landscaped areas
are in the areas of the planned addition. Gravel driveway and parking areas are
beyond the landscaping.
PROPOSED CONSTRUCTION
An addition will be constructed adjacent to the south and east sides of the
Vaughan Residence. The addition will be a one-story structure with a slab -on -grade
floor. At this writing, maximum foundation excavation depth of about 2 to 3 feet are
planned. Foundation loads are expected to be less than 2,000 pounds per lineal 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
We observed subsurface conditions exposed in two exploratory pits (TP -1 and
TP -2) excavated at the approximate locations shown on Figure 1. Existing utilities,
fences and landscaping prevented excavation of exploratory pits immediately
adjacent to the planned addition footprint. Subsurface conditions observed in the
pits were logged by our engineer who obtained samples of the excavated soils.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL 1 T JOB NO. GS -4287
2
Graphic logs of the soils observed in the exploratory pits are shown on Figure 2.
Subsurface conditions observed in the exploratory pits consisted of about 2.5
and 6 feet of silty sandy clay underlain by clayey to silty gravel with basalt cobbles
and boulders to the total explored depth of 7.5 feet. Our observations during
excavation indicated the clay was medium stiff to stiff, and the native gravel was
dense. Free ground water was not observed in our exploratory pits at the time of our
site visit The pits were backfilled immediately after exploratory excavation operations
were completed.
One sample of the natural clay was selected for one-dimensional, swell-
consolidation testing. The sample tested exhibited 3.3 percent consolidation when
wetted under an applied pressure of 1,000 psf. A sample of the natural gravel tested
contained 37 percent gravel, 44 percent sand, and 19 percent silt and clay size
particles (passing the No. 200 sieve). Test results are representative of only the
smaller size fraction of the actual soils. Swell -consolidation test results are shown on
Figure 3. Gradation test results are shown on Figure 4. Results of laboratory testing
are summarized on Table I.
SITE EARTHWORK
Excavations
We anticipate excavations for the building foundation and utilities can be
accomplished using conventional, heavy-duty excavation equipment Excavation
sides will need to be sloped or braced to meet local, state and federal safety
regulations. We believe the clay will classify as a Type B soil and the gravel will
classify as a Type C soil based on OSHA standards governing excavations.
Temporary slopes deeper than 5 feet should be no steeper than 1 to 1 (horizontal to
vertical) in Type B soils and 1.5 to 1 in Type C soils. Contractors should identify the
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL I T JOB NO. GS -4287
3
soils encountered in the excavations and refer to OSHA standards to determine
appropriate scopes.
Free ground water was not observed in the exploratory pits during exploratory
excavation 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. The
ground surrounding the excavations should be sloped as much as practical to direct
runoff away from the excavations.
Structural Fill
The silty sandy clay soil at this site possesses the potential for excessive
consolidation when wetted under load. In our opinion, unacceptable amounts of
differential movement may occur if foundations and floor slabs are constructed
directly on the in-situ, natural clay soil. We recommend removal (Le. sub -excavation)
of the clay to expose the natural gravel soil below foundations. Foundations can
then be constructed directly on the undisturbed, natural gravel. If desired, planned
foundation elevations can be re -attained by placing densely compacted, granular,
structural fill. Floor slabs should be supported on a mat of densely compacted,
granular structural fill at least 12 -inches thick. We recommend the granular,
structural fill consist of an aggregate base course, such as a CDOT Class 6 or similar
soil.
The bottom of the sub -excavated areas should be scarified to a depth of at
least 6 inches, moisture treated and compacted. Structural fill should be moisture
treated to within 2 percent of optimum moisture content and compacted to 100
percent of ASTM D 698 maximum dry density. Water required to increase the
structural fill soil moisture content to the specified moisture content should be
uniformly mixed into the fill soil prior to compaction. The actual thickness of fill lift
that can be properly compacted will depend on the type of compaction equipment.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL I T JOB NO. GS.42117
4
Our representative should observe placement and check compaction and moisture
content of the structural fill.
Backfill
Properly compacted backfill adjacent to foundation walls, retaining walls and
in utility trenches is important to reduce subsequent consolidation of backfill soils
and infiltration of surface water. Backfill soils should consist of the on-site soils, free
of rocks larger than 6 inches in diameter, organic matter and debris. Backfill should
be placed in thin lifts, moisture conditioned to within 2 percent of optimum moisture
content and compacted to at least 95 percent of standard Proctor (ASTM D 698)
maximum dry density. Density and moisture content of backfill should be checked by
a representative of our firm during construction
FOUNDATIONS
To reduce potential for differential movement between the addition and
existing residence, we recommend sub -excavation of the silty sandy clay from below
foundations to expose the gravel soil. Our representative should observe conditions
exposed in the foundation excavation. Foundations can likely be constructed directly
on the undisturbed, natural gravel. Alternatively, planned foundation elevations can
be retained with densely compacted, granular, structural fill. Recommendations for
structural fill were presented in the SITE EARTHWORK section. Settlement of the
addition will be differential with respect to the existing building. The structural
engineer should evaluate the need for construction joints between the addition and
the existing building. Recommended design and construction criteria for footing
foundations are presented below.
Footings on Natural Gravel
1. Footing foundations supported by the undisturbed, natural gravel soil
should be designed fora maximum soil bearing pressure of 4,000 psf.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL 1 T JOB NO. GS.4287
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Soils loosened during excavation or the forming process for the
footings should be removed or re -compacted prior to placing concrete.
2. To resist lateral loads, a coefficient of friction of 0.40 can be used for
friction between the footings and the sandstone.
3. Continuous wail 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.
4. Grade beams and foundation wails 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 10 feet. Reinforcement should be designed by the structural
engineer.
5. The soils under exterior footings should be protected from freezing. We
recommend the bottom of footings be constructed ata depth of at least
36 inches below finished exterior grades.
Footings on Structural Fill
1. Footing foundations supported by densely compacted, granular,
structural fila should be designed for a maximum soil bearing pressure
of 3,000 psf.
2. To resist lateral loads, a coefficient of friction of 0.35 can be used for
friction between the footings and the structural fill.
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.
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.
5. The soils under exterior footings should be protected from freezing. We
recommend the bottom of footings be constructed ata depth of at least
36 inches below finished exterior grades.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL T JOS NO. GS.42R7
5
FLOOR SYSTEM AND SLABS -ON -GRADE
The addition floor is planned as a slab -on -grade. Based on our laboratory test
data and our experience, we judge slabs -on -grade should be supported by the natural
gravel or an at least 12 -inch thick mat of densely compacted, granular, structural fill.
Structural fill placed below the floor slab should be in accordance with the
recommendations outlined in the SITE EARTHWORK section.
The most positive method to mitigate floor movement is the construction of a
structural floor with an air space between the floor and the subgrade soils. The
structural floor is supported by the foundation system. There are design and
construction issues associated with structurally supported floors, such as ventilation
and increased lateral loads, which must be considered.
We recommend the following precautions for slab -on -grade construction at
this site.
1. Slabs should be separated from exterior walls and interior bearing
members with slip joints which allow free vertical movement of the
slabs.
2. Underslab plumbing should be pressure tested for leaks before the
slabs are constructed. Plumbing and utilities which pass through slabs
should 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 residence.
These slabs should be well -reinforced to function as independent units.
4. Frequent control joints should be provided, in accordance with
American Concrete Institute (ACI) recommendations, to reduce
problems associated with shrinkage and curling. Our experience
indicates panels which are approximately square generally perform
better than rectangular areas.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CIL] T JOB NO. GS -4287
7
BELOW -GRADE CONSTRUCTION
We understand no below -grade areas are planned in the addition. if plans
change to include below -grade areas, we should be informed. Recommendations for
lateral earth pressures and subsurface drainage will be required.
SURFACE DRAINAGE
Surface drainage is critical to the performance of foundations, floor slabs and
concrete flatwork. We recommend the following precautions be observed during
construction and maintained at all times after the addition 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 12 inches in the first 10 feet
around the residence, where possible. In no case should the slope be
less than 6 inches in the first 5 feet.
2. Backfill around the exterior of foundation walls should be placed in
maximum 10 inch thick loose lifts, moisture conditioned to within 2
percent of optimum moisture content and compacted to at least 95
percent of standard Proctor (ASTM D 698) maximum dry density.
3. The building should be provided with roof 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.
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 building.
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.
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTLETJOB NO. GS -42B7
8
LIMITATIONS
The exploratory pits provide a reasonably accurate picture of subsurface
conditions. Variations in the subsurface conditions not indicated by the pits will
occur. We should observe the completed foundation excavation to confirm that the
exposed soils are suitable for support of the footings as designed.
This investigation was conducted in a manner consistent with that level of care
and skill ordinarily exercised by engineering geologists and 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 in discussing
the contents of this report or in the analysis of the influence of the subsoil conditions
on the design of the structure, please calf.
CTL 1 THOMPSON, INC.
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PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
CTL I T JOB NO. G&4287
9
SCALE: 1's 100'
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1.75' .r/4'EAS.04Er,r
370.67' O K 3-74 Z
TP -2 ■
124.0'
556.44 W
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Approximate
Locations of
Exploratory
Rats
Job No. GS -4287 Fig.1
LEGEND:
0
C.
•
0
TP -1
Clay, slily, sandy, medium
stiff to stiff, moist, brown.
(CL—ML)
Gravel, basalt cobbles and
boulders, clayey to silty,
dense, gray, brown. (GC—GM)
Indicates hand drive sample.
Indicates bulk sample.
Job No. GS --4287
TP -2
NOTES:
0-
5
NMI
IBM
10-
15—
v
•
•
1. Exploratory pits were excavated
with a backhoe on June 23,
2004. Pits were backfilled
immediately after excavation
operations were completed.
2. No free ground water was
observed In the exploratory
pits the day of excavation.
3. Locations of exploratory pits
approximate.
4. These exploratory pits are subject
to the explanations, limitations
and conclusions as contained in
this report.
are
SUMMARY LOGS OF EXPLORATORY PITS
Fig. 2
COMPRESSION % EXPANSION
4.
4.
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ADDITIONAL COMPRESSION UNDER
CONSTANT PRESSURE DUE TOWETTING
F
3 1
1 i
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11
1
0.1 1.010 too
APPUED PRESSURE - KSF
Sample of CLAY, SILTY, SANDY (CL -ML) NATURAL DRY UNIT WEIGHT= 89 PCF
From TP -1 AT 4 FEET NATURAL MOISTURE CONTENT= 14.9 %
JOB NO, GS -4287
Swell Consolidation
Test Results FIG 3
NYDROME(ERANALYSIS
25 HR. 714t TPA R!:•1CI169 US. STANDARD SERIES
AS 10N. 131,01. Ont N.19 111•01. 4101. 1 MIL 100 100 70 •40 70 16 10
SIEVE ANALYSIS
CLEAR SQUARE OPEPONOS
t
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1111
149 197 •�0 1,19 20 236 i.76 962 19.1 36.1 762 126200
DONETER OF PARTICLE IN ME METERS
CLAY olLA3TIC) TO SILT NCM.PIASTI47
SANDS
ORAVEL
FOE 1 meow ( COARSE NINE } COQUE 1 =mum
Sample of GRAVEL, CLAYEY, SILTY (GC -GM)
From TP -2 AT 5-8 FEET
1
GRAVEL 37 % SAND 44 %
SILT 8 CLAY 19 % UQUID LIMIT - %
PLASTICITY INDEX _ %
r HYDROMETER ANALYSIS
2149. 7198. TI E READ6ki5
461.01. 15 MAN. 601.04.10 A114. 4101. 1 WI. '100 100 70 •49 •30
109
LLS. SYAl1WIOSERE3
SIEVE ANALYSIS
CLEAR SOtiAREOPENINGS
19 101 •1 Sr 314 11C r rr r
.
30
20
ID
0001 0002
.006 009
.019
037 .074 149 .297 042690 1 19 20 2.36 470 962
MATER OF PARTICLE INIOLLIAETERS
CLAY (PLASTIC} TO 86.1-(N01441LAST1C)
SANCO
19.1 3E1
GRAVEL
0
10
20
30
40
501
60
70
ea
90
100
781 127 200
52
FINE 1_ M EDAN 1 COARSE FINE I COARSE 1 0361025
Sample of GRAVEL, CLAYEY, SILTY (GC -GMS
From TP -2 AT 5.8 FEET
JOB NO GS -42B7
GRAVEL 37 % SAND 44 %
SILT & CLAY 19 % LIQUID LIMIT - %
PLASTICITY INDEX : %
Gradation
Test Res u lis
FIG.
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CO
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SOIL CLASSIFICATION
!CLAY, SILTY, SANDY (CL -ML)
or
ca
a
2
J
0
co
m
0
14.
CD
CD
1
r r N
0
'Note: Swell due to wetting under an applied load of 1,000 psi. Negative values I