HomeMy WebLinkAboutHARMONY RIDGE P.U.D. SECOND REPLAT (SIX PLEX), 4608 DUSTY SAGE DR. - PDP/FDP - FDP150041 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTJanuary 28, 2014
PhilGreen Construction
1414B Blue Spruce Drive
Fort Collins, Colorado 80524
Attn: Mr. Dave Phillips (dave@philgreenco.com)
Re: Geotechnical Subsurface Exploration Report
Lot 15, Units A-F – Harmony Ridge
Fort Collins, Colorado
EEC Project No. 13-01-399
Mr. Phillips:
Earth Engineering Company, Inc. (EEC) personnel have completed the geotechnical
subsurface exploration you requested for the proposed townhome residences to be
constructed on Lot 15 of the Harmony Ridge development in Fort Collins, Colorado.
Results of the subsurface exploration are provided in this report.
We understand the proposed townhome residences will be either one or two-story wood-
frame structures with full basements. We expect foundation loads for the structure will
be light, with continuous wall loads less than 3 kips per lineal foot and individual column
loads less than 50 kips. Small grade changes are expected to develop final site grades for
the structure.
The purpose of this report is to describe the subsurface conditions encountered in the test
borings completed within the identified building envelope on the site and provide
geotechnical recommendations for design and construction of foundations and support of
floor slabs and exterior flatwork.
Lot 15 is situated in an area to the south of the intersection of Prairie Ridge Drive and
Dusty Sage Drive of the Harmony Ridge development located in Fort Collins, Colorado.
Site infrastructure, including pavements and utilities, has already been installed.
Earth Engineering Company, Inc.
EEC Project No. 13-01-399
January 28, 2014
Page 2
To develop information on existing subsurface conditions in the area of the proposed
townhomes, two soil borings were extended to depths of approximately 25 and 35 feet
below present site grades at the subject lots. The locations of the test borings were
established by pacing and estimating angles from site property corners and identifiable
site features. The locations of the borings should be considered accurate only to the
degree implied by the methods used to make the field measurements.
The borings were performed using a truck-mounted, rotary-type drill rig equipped with a
hydraulic head employed in drilling and sampling operations. The boreholes were
advanced using 4-inch nominal diameter continuous flight augers. Samples of the
subsurface materials encountered were obtained using split-barrel and California barrel
sampling procedures in general accordance with ASTM Specification D-1586. All
samples obtained in the field were sealed and returned to the laboratory for further
examination, classification and testing.
An EEC field engineer was on site during drilling to evaluate the subsurface conditions
encountered and to direct the drilling activities. Field boring logs were prepared based on
observation of disturbed samples and auger cuttings. Based on results of the field borings
and laboratory testing, subsurface conditions at the proposed residence locations can be
generalized as follows:
The near surface soils generally consisted of brown to brown/light brown and reddish
brown sandy to very sandy lean clay soils. The sandy to very sandy lean clay soils were
very stiff in consistency and contained gravel along with calcareous deposits. The sandy
to very sandy lean clay soils exhibited a low potential for swelling at current moisture
and density conditions. The sandy to very sandy lean clay soils encountered at boring B-1
were underlain by reddish brown sand and gravel materials at a depth of approximately
13 feet below present site grades and were underlain by grey/tan and rust claystone
bedrock at a depth of approximately 21 feet below present site grades at boring B-2. The
sand and gravel materials encountered at boring B-1 were dense in consistency and were
underlain by grey/tan and rust claystone bedrock at a depth of approximately 23 feet
below present site grades. The claystone bedrock encountered in the borings was
moderately hard in consistency and extended to the bottom of the borings at a depth of
approximately 25 and 35 feet below present site grades.
Earth Engineering Company, Inc.
EEC Project No. 13-01-399
January 28, 2014
Page 3
Observations were made after the completion of drilling of the borings to detect the
presence and depth to the hydrostatic groundwater table. At the time of drilling, free
water was not observed in the completed site borings. Longer-term observations in holes
which are cased and sealed from the influence of surface water would be required to
more accurately determine fluctuations in groundwater levels over time. Fluctuations in
groundwater levels can occur based on hydrologic conditions and other conditions not
apparent at the time of this report. Zones of perched and/or trapped water may also be
encountered in more permeable zones within the subgrade soils at times throughout the
year.
The stratification boundaries indicated on the boring log represent the approximate
locations of changes in soil types. Bedrock classification was based on visual and tactual
observations of disturbed samples and auger cuttings; coring and/or petrographic analysis
may reveal other rock types. In-situ, the transition of materials may be gradual and
indistinct. In addition, the soil boring provides an indication of subsurface conditions at
the test location. However, subsurface conditions may vary in relatively short distances
away from the boring. Potential variations in subsurface conditions can best be evaluated
by close observation and testing of the subgrade materials during construction. If
significant variations from the conditions anticipated from the test boring appear evident
at that time, it may be necessary to re-evaluate the recommendations provided in this
report.
ANALYSIS AND RECOMMENDATIONS
Footing Foundations
Based on materials observed at the test boring locations, it is our opinion the proposed
lightly loaded multi-family residential townhome structure could be supported on
conventional footing foundations bearing in the natural sandy to very sandy lean clay
soils. For design of footing foundations bearing on suitable very stiff sandy to very sandy
lean clay soils, we recommend using a net allowable total load soil bearing pressure not
to exceed 1,500 psf. The net bearing pressure refers to the pressure at foundation bearing
level in excess of the minimum surrounding overburden pressure.
Exterior foundations and foundations in unheated areas should be located at least 30
inches below adjacent exterior grade to provide frost protection. We recommend formed
Earth Engineering Company, Inc.
EEC Project No. 13-01-399
January 28, 2014
Page 4
continuous footings have a minimum width of 12 inches and isolated column foundations
have a minimum width of 24 inches. Trenched foundations or grade beam foundations
should not be used in the site clayey sand and sand and gravel materials.
We recommend the foundation footing design loads be balanced to promote relatively
uniform settlement, thereby reducing the potential for differential settlement. As an
alternative to balancing the design loads solely on settlement, designing the foundation
such that the dead-load pressure is balanced throughout the foundations could be
considered. Balancing the dead-load pressure would also reduce the potential for
differential settlement between adjacent footings. We estimate the long-term settlement
of footing foundations designed and constructed as recommended above would be less
than 1 inch.
No unusual problems are anticipated in the construction of the footing foundations. Care
should be taken to avoid disturbing the bearing soils. The natural site soils may be easily
disturbed by construction activities. Soils which are disturbed by the construction
activities or materials which have become dry and desiccated or wet and softened should
be reworked or removed from the foundation excavation prior to the placement of
foundation concrete.
Claystone bedrock was encountered at a depth of approximately 21 to 23 feet below
present site grades in the completed test borings. We recommend maintaining a
minimum 5-feet separation between the claystone bedrock and foundation bearing
elevation. If that separation cannot be maintained, drilled pier foundations and structural
floors would be necessary. The recommended vertical separation is a minimum and, as
such, some heaving of lightly loaded elements could occur and should be expected at the
minimum recommended vertical separation. Increasing the vertical separation between
structural elements and the underlying bedrock would reduce the potential for post-
construction heaving; however, that risk cannot be eliminated. Drilled piers and structural
floors would be needed to further reduce the potential for post-construction movement of
the proposed structure.
Care should be taken during construction to avoid disturbing the bearing materials.
Bearing materials which are loosened or disturbed by construction activities or which
become wetted and softened or dry and desiccated should be removed and replaced or
reworked in place prior to placement of reinforcing steel and foundation concrete.
Earth Engineering Company, Inc.
EEC Project No. 13-01-399
January 28, 2014
Page 5
We estimate the long-term settlement of footing foundations designed and constructed as
outlined above would be less than 1 inch.
Floor Slab and Exterior Slab-on-Grade Subgrades
Any existing vegetation and/or topsoil should be removed from floor slab areas. After
stripping and completing all cuts and prior to placement of any floor slabs or fill, we
recommend the exposed subgrades be scarified to a minimum depth of 9 inches, adjusted
in moisture content and compacted to at least 95% of the material's maximum dry density
as determined in accordance with ASTM Specification D-698, the standard Proctor
procedure. The moisture content of the scarified soils should be adjusted to be within the
range of 2% of standard Proctor optimum moisture at the time of compaction.
Scarification and compaction of subgrades in the basement area of the structure would
not be required.
Fill soils required to develop the floor slab subgrades should consist of approved, low-
volume change materials which are free from organic matter and debris. It is our opinion
the on-site soils could be used as low-volume change fill in the floor areas. Those fill
materials should be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture
content as recommended for the scarified soils and compacted to at least 95% of standard
Proctor maximum dry density.
After preparation of the subgrades, care should be taken to avoid disturbing the in-place
materials. Subgrade materials loosened or disturbed by the construction activities or
materials which become dry and desiccated or wet and softened should be removed and
replaced or reworked in place prior to placement of the floor slab concrete.
As a precaution, the floor slabs should be isolated from structural portions of the building
to prevent distress to the structure due to differential movement of the structural
elements. We also recommend isolating the basement floor slab from non-load bearing
partitions to help reduce the potential for distress in upper sections of the building due to
slab movement. That isolation is typically developed through the use of a voided wall
which is suspended from the overhead first floor joist. Care should be exercised when
framing doors, drywalling and finishing to maintain a voided space which will allow for
movement of the floor slab without transmission of stresses to the overlying structure.
Earth Engineering Company, Inc.
EEC Project No. 13-01-399
January 28, 2014
Page 6
While laboratory testing completed for this report indicated the site soils sampled
exhibited relatively low swell potential, floor slab and exterior flatwork movement could
occur and should be expected. Slab movement is common in Colorado even in areas with
relatively low-swelling soils. Mitigation techniques to reduce the potential for post-
construction movement, such as overexcavation, moisture conditioning and replacement
could be considered; however, the risk for slab movement cannot be eliminated.
Below Grade Areas
We recommend installing a perimeter drain system around all below grade areas to
reduce the potential for development of hydrostatic loads on the below grade walls and to
help prevent accumulation of infiltration water in below grade areas. In general, a
perimeter drain system should consist of perforated metal or plastic pipe placed at
approximate foundation bearing level around the exterior perimeter of the structure. The
drainline should be surrounded by a minimum of 6 inches of appropriately-sized granular
filter soil. The filter soil or the drainline should be surrounded by a filter fabric to help
reduce the potential infiltration of fines into the drain system. The drainline should be
sloped to provide gravity flow of water to a sump or gravity outfall where reverse flow
cannot occur into the system. The drain should consist of perforated pipe that is bedded
in gravel and sloped to drain to the sump pit.
Backfill placed adjacent to the below grade walls should consist of approved, cohesive
low-volume-change soils which are free from organic matter and debris. The on-site soils
could be used as fill in this area. If free draining granular soils are used as backfill
adjacent to the below grade areas, we recommend the top 2 feet of material be an
essentially cohesive material to help reduce the potential for immediate surface water
infiltration into the backfill. The backfill soils should be placed in loose lifts not to
exceed 9 inches thick, adjusted to within -1 to +3% of optimum moisture content and
compacted to be within the range 94 to 98% of the material's standard Proctor maximum
dry density.
Care should be taken in placing and compacting the wall backfill to avoid placing undue
lateral stress on the below grade walls. We recommend compacting with light
mechanical or hand compaction equipment.
Earth Engineering Company, Inc.
EEC Project No. 13-01-399
January 28, 2014
Page 7
For design of below grade walls where appropriate steps have been taken to eliminate
hydrostatic loads, we recommend using an equivalent fluid pressure of 45 pounds per
square foot per foot of depth. The recommended design equivalent fluid pressure is
based on an active stress distribution case where slight rotation is expected in the below
grade walls. The rotation expected to develop an active stress distribution case results in
deflection on the wall of approximately 0.5% times the height of the wall. That
deflection may result in stress cracks on the interior of the basement walls, particularly
near the center of spans between corners or other restrained points. The recommended
equivalent fluid pressure does not include a factor of safety or an allowance for
hydrostatic loads. Surcharge loads placed adjacent to below grade walls or point loads
placed in the wall backfill may add to the lateral pressures on below grade walls.
Other Considerations
Positive drainage should be developed away from the structure with a minimum slope of
1 inch per foot for the first 10 feet away from the building. Care should be taken in
planning of landscaping adjacent to the residence to avoid features which would pond
water adjacent to the foundations or stemwalls. Plants which require an irrigation system
and/or cause substantial fluctuations in the moisture content of the subgrade soils should
not be placed adjacent to the structure. Lawn watering systems should not be placed
within 5 feet of the perimeter of the building. Spray heads should be designed to spray
water away from the structure. Roof drains should be designed to discharge at least 5
feet away from the structure and away from paved areas.
GENERAL COMMENTS
The analysis and recommendations presented in this report are based upon the data
obtained from the soil borings performed at the indicated locations and from any other
information discussed in this report. This report does not reflect any variations which
may occur across the site. The nature and extent of such variations may not become
evident until construction. If variations appear evident, it will be necessary to re-evaluate
the recommendations of this report.
It is recommended that the geotechnical engineer be retained to review the plans and
specifications so comments can be made regarding the interpretation and implementation
of our geotechnical recommendations in the design and specifications. It is further
DRILLING AND EXPLORATION
DRILLING & SAMPLING SYMBOLS:
SS: Split Spoon - 13/8" I.D., 2" O.D., unless otherwise noted PS: Piston Sample
ST: Thin-Walled Tube - 2" O.D., unless otherwise noted WS: Wash Sample
R: Ring Barrel Sampler - 2.42" I.D., 3" O.D. unless otherwise noted
PA: Power Auger FT: Fish Tail Bit
HA: Hand Auger RB: Rock Bit
DB: Diamond Bit = 4", N, B BS: Bulk Sample
AS: Auger Sample PM: Pressure Meter
HS: Hollow Stem Auger WB: Wash Bore
Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2-inch O.D. split spoon, except where noted.
WATER LEVEL MEASUREMENT SYMBOLS:
WL : Water Level WS : While Sampling
WCI: Wet Cave in WD : While Drilling
DCI: Dry Cave in BCR: Before Casing Removal
AB : After Boring ACR: After Casting Removal
Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated
levels may reflect the location of ground water. In low permeability soils, the accurate determination of ground water levels is not
possible with only short term observations.
DESCRIPTIVE SOIL CLASSIFICATION
Soil Classification is based on the Unified Soil Classification
system and the ASTM Designations D-2488. Coarse Grained
Soils have move than 50% of their dry weight retained on a #200
sieve; they are described as: boulders, cobbles, gravel or sand.
Fine Grained Soils have less than 50% of their dry weight
retained on a #200 sieve; they are described as : clays, if they
are plastic, and silts if they are slightly plastic or non-plastic.
Major constituents may be added as modifiers and minor
constituents may be added according to the relative proportions
based on grain size. In addition to gradation, coarse grained
soils are defined on the basis of their relative in-place density
and fine grained soils on the basis of their consistency.
Example: Lean clay with sand, trace gravel, stiff (CL); silty
sand, trace gravel, medium dense (SM).
CONSISTENCY OF FINE-GRAINED SOILS
Unconfined Compressive
Strength, Qu, psf Consistency
< 500 Very Soft
500 - 1,000 Soft
1,001 - 2,000 Medium
2,001 - 4,000 Stiff
4,001 - 8,000 Very Stiff
8,001 - 16,000 Very Hard
RELATIVE DENSITY OF COARSE-GRAINED SOILS:
N-Blows/ft Relative Density
0-3 Very Loose
4-9 Loose
10-29 Medium Dense
30-49 Dense
50-80 Very Dense
80 + Extremely Dense
PHYSICAL PROPERTIES OF BEDROCK
DEGREE OF WEATHERING:
Slight Slight decomposition of parent material on
joints. May be color change.
Moderate Some decomposition and color change
throughout.
High Rock highly decomposed, may be extremely
broken.
HARDNESS AND DEGREE OF CEMENTATION:
LOT 15 – HARMONY RIDGE
FORT COLLINS, COLORADO
EEC PROJECT No. 13-01-399
DECEMBER 2013
LOT 15 - HARMONY RIDGE
FORT COLLINS, COLORADO
PROJECT NO: 13-01-399 DATE: DECEMBER 2013
LOG OF BORING B-1
RIG TYPE: CME45 SHEET 1 OF 1 WATER DEPTH
FOREMAN: SM START DATE 12/26/2013 WHILE DRILLING None
AUGER TYPE: 4" CFA FINISH DATE 12/26/2013 AFTER DRILLING None
SPT HAMMER: AUTO SURFACE ELEV N/A 24 HOUR N/A
SOIL DESCRIPTION D N QU MC DD A-LIMITS -200 SWELL
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF
_ _
SANDY TO VERY SANDY LEAN CLAY (CL) 2
brown to brown/light brown CS _ _ 8 9000+ 11.4 98.5 1000 psf 0.3%
very stiff 4
with gravel SS _ _ 8 9000+ 8.4
6
_ _
8
_ _
very sandy CS 10 15 9000+ 8.2 116.9 600 psf 0.1%
_ _
12
_ _
14
SAND AND GRAVEL (SP-GP) SS _ _ 50 -- 5.2
reddish brown 16
dense _ _
18
_ _
SS 20 30 -- 5.8
_ _
22
_ _
CLAYSTONE 24
grey/tan/rust, moderately hard SS _ _ 50 9000+ 17.2
25' BOTTOM OF BORING 26
_ _
28
_ _
30
_ _
32
_ _
34
_ _
36
_ _
38
_ _
40
_ _
42
_ _
44
_ _
46
_ _
48
_ _
50
LOT 15 - HARMONY RIDGE
FORT COLLINS, COLORADO
PROJECT NO: 13-01-399 DATE: DECEMBER 2013
LOG OF BORING B-2
RIG TYPE: CME45 SHEET 1 OF 1 WATER DEPTH
FOREMAN: SM START DATE 12/26/2013 WHILE DRILLING None
AUGER TYPE: 4" CFA FINISH DATE 12/26/2013 AFTER DRILLING None
SPT HAMMER: AUTO SURFACE ELEV N/A 24 HOUR N/A
SOIL DESCRIPTION D N QU MC DD A-LIMITS -200 SWELL
TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF
_ _
SANDY LEAN CLAY (CL) 2
brown _ _
very stiff 4
silty with calcareous deposits CS _ _ 14 9000+ 10.6 97.0 35 17 63.5 800 psf 0.4%
6
_ _
8
_ _
reddish brown SS 10 12 8500 15.9
_ _
12
_ _
14
CS _ _ 16 7000 15.8 112.2 < 1000 psf None @ 1000
16
_ _
18
_ _
grey/brown/rust SS 20 14 8000 13.3
with gravel _ _
22
CLAYSTONE _ _
grey/tan/rust 24
moderately hard CS _ _ 48 8500 15.0
26
_ _
28
_ _
30
_ _
32
_ _
34
_ _
35' BOTTOM OF BORING 36
_ _
38
_ _
40
_ _
42
_ _
44
_ _
46
_ _
48
_ _
50
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy to Very Sandy Lean Clay with Gravel
Sample Location: B-1, S-1 @ 2'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 13.7% Dry Density: 98.5 pcf Ending Moisture: 23.3%
Swell Pressure: 1000 psf % Swell @ 500 psf: 0.3%
Project: Lot 15 - Harmony Ridge
Fort Collins, Colorado
Project No.: 13-01-399
Date: December 2013
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Very Sandy Lean Clay with Gravel
Sample Location: B-1, S-3 @ 9'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 7.2% Dry Density: 116.9 pcf Ending Moisture: 16.6%
Swell Pressure: 600 psf % Swell @ 500 psf: 0.1%
Project: Lot 15 - Harmony Ridge
Fort Collins, Colorado
Project No.: 13-01-399
Date: December 2013
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Brown Sandy Lean Clay
Sample Location: B-2, S-1 @ 4'
Liquid Limit: 35 Plasticity Index: 17 % Passing #200: 63.5
Beginning Moisture: 10.0% Dry Density: 97.0 pcf Ending Moisture: 23.6%
Swell Pressure: 800 psf % Swell @ 500 psf: 0.4%
Project: Lot 15 - Harmony Ridge
Fort Collins, Colorado
Project No.: 13-01-399
Date: December 2013
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
SWELL / CONSOLIDATION TEST RESULTS
Material Description: Reddish Brown Sandy Lean Clay
Sample Location: B-2, S-3 @ 14'
Liquid Limit: -- Plasticity Index: -- % Passing #200: --
Beginning Moisture: 14.1% Dry Density: 112.2 pcf Ending Moisture: 18.2%
Swell Pressure: < 1000 psf % Swell @ 1000 psf: None
Project: Lot 15 - Harmony Ridge
Fort Collins, Colorado
Project No.: 13-01-399
Date: December 2013
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.01 0.1 1 10
Percent Movement
Load (TSF)
Water Added
Consolidation Swell
Earth Engineering Company
Earth Engineering Company
Limestone and Dolomite:
Hard Difficult to scratch with knife.
Moderately Can be scratched easily with knife.
Hard Cannot be scratched with fingernail.
Soft Can be scratched with fingernail.
Shale, Siltstone and Claystone:
Hard Can be scratched easily with knife, cannot be
scratched with fingernail.
Moderately Can be scratched with fingernail.
Hard
Soft Can be easily dented but not molded with
fingers.
Sandstone and Conglomerate:
Well Capable of scratching a knife blade.
Cemented
Cemented Can be scratched with knife.
Poorly Can be broken apart easily with fingers.
Cemented