HomeMy WebLinkAboutPLATT PROPERTY PUD PRELIMINARY - 3 90B - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTREPORT
OF A
GEOTECHNICAL INVESTIGATION
FOR
VILLAGES AT HARMONY WEST
FORT COLLINS, COLORADO
THE GROUP, INC.
FORT COLLINS, COLORADO
PROJECT NO. 8299-90
BY
EMPIRE LABORATORIES, INC.
301 NORTH HOWES STREET
FORT COLLINS, COLORADO 80521
shrinkage factor of fifteen percent (15%) to twenty percent (20%) may be
used for the bedrock used as compacted fill.
All excavations should be dug on safe and stable slopes, It is
suggested that excavated soil slopes be on minimum grades of 1-1 /2:1 or
flatter. The bedrock may be excavated on near -vertical slopes. The
slope of the sides of the excavations should comply with local codes or
OSHA regulations. Where this is not practical, sheeting, shoring and/or
bracing of the excavation will be required. The sheeting, shoring and
bracing of the excavation should be done to prevent sliding or caving of
the excavation walls and to protect construction workers and adjacent
structures. The side slopes of the excavation or sheeting, shoring or
bracing should be maintained under safe conditions until completion of
backfilling. In addition, heavy construction equipment should be kept a
safe distance from the edge of the excavation.
Where utilities are excavated below ground water, dewatering will be
needed during placement of pipe and backfilling for proper construction.
All piping should be adequately bedded for proper load distribution.
Backfill placed in utility trenches in open and planted areas should be
compacted in uniform lifts at optimum moisture to at least ninety percent
(90%) of Standard Proctor Density ASTM D 698-78 the full depth of the
trench. The upper four (4) feet of backfill placed in utility trenches
under roadways and paved areas should be compacted at or near optimum
moisture to at least ninety-five percent (95%) of Standard Proctor
Density ASTM D 698-78, and the lower portion of these trenches should
be compacted to at least ninety percent (90%) of Standard Proctor
Density ASTM D 698-78. Addition of moisture to and/or drying of the
subsoils may be needed for proper compaction. Proper placement of the
bedrock as backfill may be difficult.
Stripping, grubbing, subgrade preparation, and fill and backfill
placement should be accomplished under continuous observation of the
geotechnical engineer. Field density tests should be taken daily in the
compacted subgrade, fill, and backfill under the direction of the
geotechnical engineer.
Laboratory resistivity tests, pH, oxidation-reduction potential and
sulfide tests performed in the laboratory indicate that the subsoils at
-7-
the site are slightly corrosive, and protection of metal utility pipe, in
our opinion, is recommended.
Foundations
In view of the loads transmitted by the proposed residential
construction and the soil conditions encountered over the majority of the.
site, it is recommended that the structures in the northern two-thirds of
the property placed a minimum of three (3) feet above the bedrock
stratum be supported by conventional -type spread footi.ngs and/or grade
beams. All footings and/or grade beams should be founded on the
original, undisturbed soil or on a structural fill extended to the
undisturbed soil a minimum of thirty (30) inches below finished grade for
frost protection. The structural fill should be constructed in accordance
with the recommendations discussed in the "Site Grading, Excavation and
Utilities" section of this report. The structural integrity of the fill as
well as the identification and undisturbed nature of the soil should be
verified by the geotechnical engineer prior to placement of any
foundation concrete. Footings and/or grade beams founded at the above
levels may be designed for a maximum allowable bearing capacity of two
thousand (2000) pounds per square foot (dead load plus maximum live
load). To counteract swelling pressures which will develop if the
subsoils become wetted, all footings and/or grade beams should be
designed for a minimum dead load of seven hundred fifty (750) pounds
per square foot.
The predicted settlement under the above maximum loading, as
determined by laboratory consolidation tests, should be less than
three -fourths (3/4) inch, generally considered to be within acceptable
tolerances.
Structures founded in or within three (3) feet of the bedrock
stratum should be supported by a drilled pier foundation system. It is
anticipated that structures founded in the southern one-third of the
property in the area of Borings 6 and 10 through 12 will extend into or
within three (3) feet of the bedrock and will require drilled pier
foundations. Using this type of foundation system, the structure is
-8-
supported by piers drilled into the bedrock stratum and structural grade
beams spanning the piers. Piers should be straight -shaft and should be
drilled within plumb tolerances of one and one-half percent
relative to the length of the pier. The piers are supported by the
bedrock stratum partially through end bearing and partially through skin
friction. It is recommended that all piers have minimum ten (10) foot
lengths and that they he drilled a minimum of three (3) feet into the
firm bedrock stratum. Piers founded at the above level may be designed
for a maximum allowable end bearing pressure of twenty thousand
(20,000) pounds per square foot. It is estimated that a skin friction of
two thousand (2000) pounds per square foot will be developed for that
portion of the pier embedded three (3) feet into the firm bedrock
stratum. To counteract swelling pressures which will develop if the
subsoils become wetted, all piers should be designed for a minimum dead
load of five thousand (5000) pounds per square foot. Where this
minimum dead load requirement cannot be satisfied, it is recommended
that skin friction from additional embedment into the firm bedrock be
used to resist uplift. To help provide the required skin friction, the
sides of the pier drilled into the bedrock stratum should be roughened..
All piers should be reinforced their full length to resist tensile stresses
created by swelling pressures acting on the pier. It is recommended
that all grade beams have a minimum four (4) inch void between the
bottom of the beam and the subsoil below. The predicted settlement
under the above maximum loading should be negligible. Drilled piers
should be designed to resist all induced lateral forces. Since no free
around water was encountered in the southern portion of the site where
drilled piers are required, it is our opinion that temporary casing of the
drill holes will not he required. It is recommended that all piers should
have minimum ten (10) to twelve (12) inch diameters.
It is strongly recommended that the geotechnical engineer be
present during the drilling operations to (1) identify the firm bedrock
stratum, (2) assure that proper penetration is obtained into the sound
bedrock stratum, (3) ascertain that all drill holes are thoroughly
roughened, cleaned and dewatered prior to placement of any foundation
-9-
concrete, (4) check all drill holes to assure that they are plumb and of
the proper diameter, and (5) ensure proper placement of concrete and
reinforcement. ,
.Basements, Dewatering_Systems and Slabs on Grade
In view of the depth to ground water and/or bedrock encountered at
the site, it is our opinion the majority of the site is suitable for
basement construction. Due to the shallow depth to bedrock encountered
in the southern third of the site, it is recommended that. complete
dewatering systems be provided around any portion of structures placed
in or within three (3) feet of the bedrock and/or ground water.
The deinwatering system should contain a four (4) inch diameter
perforated pipe, underslab gravel, a sump and pump, or other suitable
drain outlet. The perforated pipe should be placed around the entire
perimeter of the lower basement area. All piping in the perimeter trench
should be surrounded by clean, graded gravel from three -fourths (3/4)
inch to the #4 sieve in accordance with ASTM C 33-78, Size. No. 67
The gravel should extend from at least three (3) inches below the bottom
of the pipe to a minimum of two (2) feet above the bedrock and/or
ground water above the pipe, the full width of the trench. To minimize
the cost of gravel backfill, it is suggested that the excavation be limited
to the area necessary for construction; however, the trench should he a
minimum of twelve (12) inches wide. The top of the gravel backfill
adjacent to foundation walls should be covered with .an untreated
building paper to help minimize clogging of the medium with earth
backfill. To minimize the potential for surface water to enter the
system, it is recommended that a clay backfill be placed over the system
and compacted at or near optimum moisture to at least ninety-five
percent (95%) of Standard Proctor Density ASTM D 698-78. (See
Appendix C.) We recommend that the drainage pipe be placed at least
one (1) foot below the finished slab and have a minimum grade of
one -eighth (1 /8) inch per foot. All lower level slabs surrounded by
perimeter drains should be underlain by a minimum of eight (8) inches of
clean, graded gravel or crushed rock devoid of fines. The drainage
-10-
system should empty into a sewer underdrain should one adequately
sized to accept the anticipated flows exist at the site, or the water from
the drain should empty into a sump provided in the lower basement area.
The sump should be a minimum of eighteen (18) inches in diameter and
three (3). feet deep. A minimum of one (1) foot of clean, graded gravel
meeting the above specifications should be placed adjacent to the bottom
and sides of the sump. The sump should be provided with a pump
designed to discharge all flow to the sump. Water from the sump should
be disposed of by suitable means well beyond the foundation of the
residence.
Due to the swelling pressures exerted by the materials at subgrade,
it is our opinion that the only positive solution for construction of
the slab where movement will not occur is a structural floor with a void
beneath it. However, the cost of this type of system may be prohibitive.
It is our opinion that, with certain precautions and knowing that some
risk is involved, a floating floor slab may be a reasonable alternative.
If the owner is willing to assume the risk of future slab movement and
related structural damage, the following recommendations may reduce slab
movement and its adverse effects.
Subarade below slabs on grade at the upper level should be
prepared in accordance with the recommendations discussed i.n the "Site
Grading, Excavation and Iltilities" section of this report. If the
subgrade below slabs on grade is allowed to dry below the required
moisture, the subgrade should be rescarified and recompacted to two
percent (2%) wet of optimum moisture to the required density just prior
to placement of underslab gravel and concrete. Slabs on grade should
be underlain by a minimum of four (4) inches of clean, graded gravel or
crushed rock devoid of fines. Slabs surrounded by perimeter drains
should be underlain by a minimum of eight (8) inches of clean, graded
gravel or crushed rock devoid of fines. Garage slabs should be
reinforced with wire mesh running through the control joints. Slabs on
grade should be designed and constructed structurally independent of
bearing members.
To minimize and control shrinkage cracks which may develop in slabs
on grade, we suggest that control joints be placed every fifteen (15) to
-11-
twenty (20) feet and that the total area contained within these joints
be no greater than four hundred (400) square feet. In addition, if
building construction is done during winter months, it is recommended
that slabs on grade not be placed on frozen ground and that they be
protected from freezing temperatures until they are properly cured.
We further recommend that nonbearing partitions placed on floor
slabs be provided with a slip joint (either top or bottom). Slip joints
reduce pressure applied by heaving floor slabs and thus minimize damage
to the portion of the structure above. It is emphasized that if the
subsoils are kept dry, movement of slabs on grade should be minimal.
However, if moisture is permitted to reach the subsoils below the slabs,
heaving will probably occur.
Pavement
At the time this report was prepared, the locations of the proposed
streets within the subdivision had not been determined. However,
general recommendations for streets have been provided, and pavement
thicknesses for a typical residential street are provided. Final pavement
design will be provided after street locations are determined.
It is our opinion that flexible pavement is suitable for the proposed
street construction at the site. A flexible pavement alternate should
consist of asphalt concrete underlain by crushed aggregate base course
or asphalt concrete underlain by plant mix bituminous base course. The
design criteria described below was utilized in determining the pavement
thicknesses at the site.
City of Fort Collins "Design Criteria and Standards for Streets"
dated July 1986
"R" value - 6
Regional Factor - 1.0
Serviceability Index - 2.0 for residential streets and 2.5 for collector
streets
20-Year Design Life
-12-
18 kip Equivalent Daily Load Application - 10 assumed for typical
residential street
Residential Streets
Asphalt Concrete 3"
Crushed Aggregate Base Course 12"
Total Pavement Thickness 15"
Asphalt Concrete 2"
Plant Mix Bituminous Base Course 5"
Total Pavement Thickness 7"
The crushed aggregate base course should meet City of Fort Collins
Class 5 or 6 specifications. The subgrade below the proposed asphalt
pavement should be prepared in accordance with the recommendations
discussed in the "Site Grading, Excavation and Utilities" section of this
report. Upon proper preparation of the subgrade, the base course
should be placed and compacted at optimum moisture to at least
ninety-five percent (95%) of Standard Proctor Density ASTM n 698-78.
(See Appendix C.)
It is recommended that the asphalt concrete and/or plant mix
bituminous base course he placed in two (2) to three (3) inch Lifts. All
plant mix bituminous base course and asphalt concrete shall meet City of
Fort Collins specifications and should be placed in accordance with these
specifications. The crushed aggregate base course shall have an "R"
value between 70 and 77, the plant mix bituminous base course shall
have an Rt value of 90 or greater, and the asphalt concrete shall have
an Rt value of 95 or greater. The "R" value of the pavement materials
Used should be verified by laboratory tests. Field density tests should
be taken in the aggregate base course, bituminous base course, and
asphalt concrete under the direction of the geotechnical engineer.
Rigid Pavement
A feasible pavement alternate at the site would be rigid pavement.
Using the eighteen (18) kip equivalent daily load application described
-13-
above, a modulus of subgrade reaction of one hundred (100) pounds per
square inch per inch based on an "R" value of 6, a design life of twenty
(20) years, and concrete designed with a modulus of rupture of six.
hundred (600) pounds per square inch using the above assumed 18 kip
EDLA of 10, a minimum pavement thickness of five (5) inches of
nonreinforced concrete is recommended.
Subgrade below proposed streets should be prepared in accordance
with the recommendations discussed in the "Site Grading, Excavation and
Utilities" section of this report. Concrete pavement should be placed
directly on the subgrade that has been uniformly and properly prepared
in accordance with the above recommendations. All concrete used in the
paving shall meet ASTM specifications, and all aggregate shall conform to
ASTM C-33 specifications. The concrete should be designed with a
minimum modulus of rupture of six hundred (600) pounds per square inch
in twenty-eight (28) days. It is recommended that laboratory mix
designs be done to determine the proper proportions of aggregates,
cement, and water necessary to meet these requirements. It is essential
that the concrete have a low water -cement ratio, an adequate cement
factor, and sufficient quantities of entrained air. Joints should be
carefully designed and constructed in accordance with the City of Fort
Collins "Design Criteria and Standards for Streets" to ensure good
performance of the pavement. It is recommended that all concrete
pavement be placed in accordance with City of Fort Collins
specifications. If paving is done during cold weather, acceptable cold
Weather procedures as outlined in the City specifications should be.
utilized. The concrete pavement should be properly cured and protected
in accordance with the above specifications. Concrete injured by frost
should be removed and replaced. It is recommended that the pavement
not be opened to traffic until a flexural strength of four hundred (400)
pounds per square inch is obtained or a minimum of fourteen (14) days
after the concrete has been placed.
-14-
GENERAL RECOMMENDATIONS
(1) Laboratory test results indicate that water soluble sulfates in
the soil are negligible, and a Type 1-II cement may be used in
concrete exposed to subsoils. Slabs on grade subjected to
de-icing chemicals should be composed of a more durable
concrete with low water -cement ratios and higher air contents.
(2) Finished grade should be sloped away from the structures on all
sides to give positive drainage. Ten percent (10%) for the first
ten (10) feet away from the structures is the suggested slope.
(3) Rackfill around the outside perimeter of the structures should
be mechanically compacted at optimum moisture to at least ninety
percent (90%) of Standard Proctor Density ASTM D 698-78.
(See Appendix C.) Puddling should not be permitted as a
method of compaction.
(4) Gutters and downspouts should be designed to carry roof
runoff water well beyond the backfill area.
(5) Underground sprinkling systems should be designed such that
piping is placed a minimum of five (5) feet outside the backfill
of the structures. Heads should be desiqned so that irrigation
Water is not sprayed onto the foundation walls. These
recommendations should be taken into account in the. landscape.
planning.
(6) Plumbing under slabs should be eliminated wherever possible
since plumbing failures are quite frequently the source of free
water which may cause slab heave.
(7) Footing, grade beam and/or pier sizes should be proportioned
to equalize the unit loads applied to the soil and thus minimize
differential settlements.
-15-
(8) It is recommended that compaction requirements specified herein
be verified in the field with density tests performed under the
direction of the geotechnical engineer.
(9) It is recommended that a registered professional engineer design
the substructures and that he take into account the findings
and recommendations of this report.
GENERAL COMMENTS
This report has been prepared to aid in the evaluation of the
property and to assist the architect and/or engineer in the design of
this project. In the event that any changes in the design of the
structures or their locations are planned, the conclusions and
recommendations contained in this report will not be considered valid
unless said changes are reviewed and conclusions of this report modified
or approved in writing by Empire Laboratories, Inc., the geotechnical
engineer of record.
Every effort was made to provide comprehensive site coverage
through careful locations of the test borings, while keeping the site
investigation economically viable. Variations in soil and ground water
conditions between test borings may be encountered during construction.
In order to permit correlation between. the "reported subsurface conditions
and the actual conditions encountered during construction and to aid in
carrying out the plans and specifications as originally contemplated, it is
recommended that Empire Laboratories, Inc. he retained to perform
continuous construction review during the excavation and foundation
phases of the work. Empire Laboratories, Inc. assumes no responsibility
for compliance with the recommendations included in this report unless
they have been retained to perform adequate on -site construction review
during the course of construction.
-16-
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GEOTECHNICAL ENGINEERING 8 MATERIALS TESTING
January 18, 1990
The Group, Inc.
323 South College Avenue
Fort. Collins, Colorado 80524
Attention: Ms. Linda Hopkins
Gentlemen:
CORPORATE OFFICE
P.O. Box 503 • 301 No. Howes
Fore Collins, Colorado eos22
(303) 484-0359
FAX No. (303) 484-0454
We are pleased to submit our Report of a Geotechnical Investigation
prepared for the proposed residential development located on Seneca
Street in southwest Fort Collins, Colorado.
Based upon our findings in the subsurface, it is our opinion the site is
suitable for the proposed construction, providing the design criteria and
recommendations set forth in this report are met. The accompanying
report presents our findings in the subsurface and our recommendations
based upon these findings.
Very truly yours,
EMPIRE LABORATORIES INC 71
Neil R. herrod
Senior Engineering Geologist
Reviewed by:
F
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Chester C. Smith, P.F.
a N 4806 i
President
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'?F OF COV
::raeu(oslaua -`
Branch Of em
P.O. Boa I M59 P.O. Box 1135 P.O. Box 17" P.O., Box 5869
Colorado SPrin946 CO So935 Longmont, CO 80602 Greeley, CO 80632 Cheyenne, WY 82003
tiff)) 597-2116 (303) 770.3921 (303) 351.0480 (307) OU-9224
Member of ConstibV Engineers Council
RESISTRNCE R-VHLUE'HND EXPRNSION PRESSURE
OF COMPACTED SOIL
RSTM — D 2844
CLIENT: THE GROUP. INC.
PROJECT: THE VILLAGES AT HARMONY WEST
LOCATION OF SAMPLE: COMPOSITE SAMPLE BORING NO. 9 @ 0.5' - 3.5'
SAMPLE DATA
TEST SPECIMEN
I.
2.
3
COMPACTION PRESSURE
- PSI
0
0
20
DENSITY - PCF
95.1
97.6
104.4
MOISTURE - %
28.0
25.5
21.0
EXPANSION PRESSURE
- PSI
0.08
0.00
0.00
HORIZONTAL PRESSURE
@ 160 psi
155
148
139
SAMPLE HEIGHT - in..
2.52
2.56
2.56
EXUDATION PRESSURE
- PSI
111
219
358
UNCORRECTED R-VALUE
1.6
4.0
8.2
CORRECTED R-VALUE
1.6
4.1
8.4
R-VALUE AT 300 PSI EXUDATION PRESSURE = 5.8
100
402
W 60
J
2
m 40
20
dai
260 300 400 500 600
EXUDATION PRESSURE — psi
EMPIRE LABORATORIES INC.
0
B-5
SUMMARY OF TEST RESULTS
Boring
Depth
Me lsturs
Dry
Density
Compressive
Strength
Swell
Pressure
Soluble
Sulfates
PH
Liquid
Limit
Plasticity
Index '
G►ouP
Index
ClessHication
AASHTO
Resistivity
(OHM�M)
Penetration
Blows/in.
IFt.I
I %1
IPCFI
IPSFI
IPSF)
1%1
1%1
1%1
LISCS
1
0.5-1.5
18.9
18/12
3.0-4.0
18.7
90.8
820
4.0-5.0
17.9
4/12
7.0-8.0
19.2
107.6
2370
8.0-9:0
18.3
7/12
14.0-15.0
19.0
12/12
Composi
Sample'
e
0.5-3.5
44.3
21.6
15.7
OL A-7(16)
2
0.5-1.5
17.8
21/12
3.0-4.0
16.7
107.8
3400
155
4.0-5.0
18.8
7/12
7.0-8.0
16.2
106.4
1900
8.0-9.0
18.8
5/12
14.0-14.7
12.9
50/8
3
0.5-1.5
19.5
22/12
&.0-4.0
23.1
89.7
2430
.0025
4.0-5.0
22.3
5/12
7.0-8.0
13.5
118.2
1900
8.0-9.0
10.1
13/12
14.0-15.0
13.3.
50/12
emrmc Lgeun.a 1 umca. 1.uc
SUMMARY OF TEST RESULTS
Boring
Dopth
Moisturo
Dry
Density
Compressive
Strength
Swell
Pressure
Soluble
Sulfates
1IiH
Liquid
Limit
Plasticity
Index
Group
Index
Classification
AASHTO
USCS
Resistivity
(OHM CM)
Penetration
Blows/In.
No.
IFt
(%)
(PCF)
IPSFI
IPSFI
1%1
4
0.5-1.5
11.0
20/12
3.0-4.0
13.8
*285
4.0-5.0
4.3
28/12.
7.0-8.0
9.8
18/12
14.0-15.0
11.9
36/12
Composi:
Sample
e
0.5-3.5
31.3
12.7
1.7
SL A-6 (2)
5
0.5-1.5
12.6
22/12
3.0-4.0
6.3
4.0-5.0
5.6
6/12
%0.8.0
10.1
114.6
310
8.0-9.0
14.4
4/12
14.0-15.0
12.5
30/12
6
0.54.5
22.0
9/12
3.0-4.0
9.2
120.3
6050,
280
4.0-5.0
7.1
25/12
7.0-8.0
4.5
8.0-:9.0
11.5
48/12
14.0-14.3
12.2
*1290
50/4
e
o remolded
samplg
cmrinc UMWwn..1
• SUMMARY OF TEST RESULTS
Boring
Depth
Moisture
Density
.Compressive
Strength
Swell
Pressure
Soluble
Sulfat
Sulfate
pH
PH
Liquid
Limit
Plasticity
Index
Group
Index
Cls wfwittion
AASHTO
Resistivity
(OHM4m)
Penetration
Blows/In.
No. >
IFt.I
1%)
IPCFI
(PSFI
(PSF)
1%)
M
(%1
USCS
7
0.5-1.5
13.8
24/12
3.0-4.0
10.0
94.3
3710
4.0-5.0
11.2
17/12
7..0-8.0
10.3
97.1
2360
.0031
8.0-9.0
6.0
30/12
14.0-14.7
10.5
50/8
8
0.5-1.5
13.4
17/12
3.0-4.0
10.4
88.3
3530
1060
4.0-5.0
10.5
18/12
8.0-9.0
3.0
24/12
14.0-14.3
6.2
50/4
9
0.5-1.5
8.9
16/12
3.0-4.0
17.9
98.1
1630
4.0-5.0
15.9
7/12
7.0-8.0
7.0
8.0-9.0
2.9
20/12
14.0-15.0
14.8
.0017
20/12
cmpos j
e.
Simple'
'` Q.5-3.5
36.1
16.,5
7.5
CL A-6(7.5)
;,;...
IL
EMPIRE LAaURA I UNIC6.1N6.
SUMMARY OF TEST RESULTS
Boring
Depth.
moisture
Dry
Density
Compressive
Stronpth
Swell
Pressure
Soluble
Sulfates
pH
Liquid
Limit
Plasticity
Index
Group
Index
Classification
AASHTO
Resistivity
(OHM -CM)
penetration
Blowslln.
hto.
IFt.)
1%)
IPCF)
IPSF)
IPSF)
I%)
1%1
I%1
IISCS
10
0.5-1.5
9.9
22/12
3.0-4.0
8.3
104.5
1850
4.0-5.0
8.5
50/12
8.0-8.7
11.1
50/8
14.0-14.3
10.5
50/3
11
0.5-1.5
17.4
15/12
3.0-4.0
7.4
4.0-5.0
4.3
50/12
7.0-7.7
9.1
750
50/8
14.0-14.3
8.2
50/3
Composi
e
Sample
0.5-1.5
41.4
21
10
CL A-700)
12
0.5-1.5
8.6
I
19/12
3.0-4.0
7.9
106.5
1980
4.0-5.0
8.4
5/12
7.0-8.0
15.4
99.3
1600
8.0-9.0
11.7
31/12
14.0-14.7
--------------
9..5
50/8
CMromr. Lj%ounot 1 Vngra. Irvb.
Boring
No.
Depth
(ft.)
SUMMARY
%
Moisture
OF TEST RESULTS
Resistivity
ohm/cm
Oxidation -Reduction Sulfide pH
Potential (MV)
1
0.5-3.5
23.7
1200
255 trace 7.7
9
0.5=3.5
25A
2400
218 trace 7 5
No Text
APPENDIX C.
Suggested Minimum Specifications for Placement of Compacted
Earth Fill and/or Back-fill.s
GENERAL
The geotechnical engineer shall be the owner's, architect's,..
engineer's or contractor's representative to observe placement of.
compacted fill and/or backfill on the project. The geotechnical engineer.
or his representative shall approve all earth materials prior to their. use, _
the method of placement and the degree of compaction.
MATERIALS
Soils used for all compacted fill and backfiil shall be approved by
the geotechnical engineer or his representative prior to their use. Fill
material shall be free from organic matter, frozen material and other
unsuitable substance and shall not contain rocks or lumps having a
diameter greater than six (6) inches.
SUBGRADE PREPARATION
All topsoil,
vegetation, trees, brush, timber, debris, rubbish and all
other unsuitable
material shall be removed to a depth satisfactory to the
geotechnical engineer or his representative. The material shall be
beginning of the
disposed of by
subgrade. The
suitable means prior to preparation
subgrade shall be scarified a minimum depth of six (6)
inches, moisture
conditioned as necessary and compacted in a suitable
fill material. Fill shall not be placed until
manner prior to
approval by the.
placement of
geotechnical engineer or his representative: and in -no
case, shall fill
material be placed on frozen or unstable ground.
require the use of imported granular
Subgrade which is not stable may
material, geotextiles or other methods for stabilization as approved by the
geotechnical engineer.
FILL PLACEMENT
Fill material shall not
be placed during unfavorable.. weather
fill shall be approved by the
conditions. Material
engineer
proposed for use as
or his representative prior to use.
Proposed import.
his
geotechnical
material shall be
approved
by the geotechnical
Fill
engineer or
material shall be..
representative prior to hauling
to the project site.
C=2
,..
uniformly mixed such as to preclude the formation of lenses ofmaterial
differing from the surrounding material. All clods shall be broken into
small pieces. The contractor shall construct the fill in approximately
horizontal lifts extending the entire length of the fill. The thickness of
the layers before compaction shall not be greater than eight (8) inches..
Fill being placed on slopes or hillsides shall be benched into the existing
slope. A minimum two (2) foot horizontal bench shall be cut into the
existing excavated slope for each four (4) feet vertical of fill, or each lift
should be benched slightly into the existing grade.
MOISTURE CONTROL
Prior to and during compaction operations, the fill material being
placed shall be maintained within the range of optimum moisture specified.
A general recommendation is to maintain the fill material within two
percent (2%) plus or minus of optimum moisture so that proper compaction
to the specified density may be obtained with a minimal effort. In
building .pad and paved areas, material exhibiting swelling potential shall
be maintained between optimum moisture and two percent (2%) wet of
optimum. moisture content. The moisture content of the fill material shall
be maintained uniform throughout the fill. The contractor may be.
required to add necessary moisture to the fill material and to. uniformly
mix the water with the fill material if, in the opinion of the geotechnical
engineer, it is not possible to obtain uniform moisture content by adding
water on the fill surface. If, in the opinion of the geotechnical engineer,
the material proposed for use in the compacted fill is too wet -to permit'
adequate compaction, it shall be dried in an acceptable manner prior to
placement and compaction. Uniform mixing may require discing, blading
or other methods approved by the geotechnical engineer or his
representative.
Adjustments of moisture content shall be made on the basis of
determinations of moisture content by field tests as construction
progresses.
COMPACTION
The contractor shall furnish and operate the necessary types and
kinds of equipment to perform the operations required to obtain the
specified compaction. This equipment may include approved tamping
rollers, rubber tired rollers, smooth wheeled rollers and vibratory
rollers. If a sheepsfoot roller is used, it shall be provided with cleaner
bars so attached as to prevent the accumulation of material between the
tamper feet. Fill areas which are not accessible to full-sized construction
equipment. shall be placed in maximum four (4) inch lifts and compacted
with power tampers to the specified density.
C-3
Compaction should meet the minimum percentages of maximum density
as set forth in the project specifications or the recommendations of the
report. The contract specifications supercede the recommendations 'given
in this report.
MOISTURE DENSITY RELATIONSHIP DETERMINATION
Samples of representative fill materials to be placed shall. be
furnished by the contractor to the geotechnical engineer for determination
of maximum density and optimum moisture or relative density. Sufficient
laboratory moisture density or relative density curves will be. made to
determine the optimum moisture content and maximum density for the
various soils placed as fill. Tests for this determination will bemade
using the appropriate method conforming to the requirements of ASTM D
698 (Standard Proctor), ASTM D 1557 (,Modified Proctor) or ASTM D 4253,
D 4254 (Relative Density). The materials used for fill shall be classified
in accordance with ASTM D 2487 in order to permit correlation between
the moisture density relationship data and the material being placed and
compacted.. Copies of the results of these tests will be furnished to the
client and others as directed by the client. These test results shall be
the basis of control for all compaction effort.
FIELD DENSITY AND MOISTURE TESTS
The in -place density and moisture content of compacted fill will be
determined by the geotechnical engineer or his representative in
accordance with ASTM D 1556 (sand cone method) or ASTM D 2922, D
3017 (nuclear methods). Material not meeting the required compaction
and/or moisture specifications shall be recompacted and/or moisture.
conditioned until the required percent compaction and/or moisture content
is obtained. Sufficient compaction tests shall be made and submitted to
support the geotechnical engineer's or his representative's
recommendations. The results of density tests will also be furnished to
the client and others as directed.
C-4
REPORT
OF A
GEOTECHNICAL INVESTIGATION
This report presents the results of a geotechnical evaluation
prepared for the proposed residential development located west of the
Pleasant Valley and Lake Canal between Troutman Parkway and Wake.
Robin Lane in southwest Fort Collins, Colorado. The investigation
included test borings and laboratory testing of samples obtained from
these borings.
The objectives of this study were to (1) evaluate the subsurface
conditions at the site relative to the proposed construction, (2) make
recommendations regarding the design of the substructures; (3)
recommend certain precautions which should be taken because of adverse
soil and/or ground water conditions, and (4) make recommendations
regarding pavement types and thicknesses for the proposed streets to be
constructed at the site.
SITE EXPLORATION
The field exploration, carried out on January 10, 19.90, consisted of
drilling, logging, and sampling twelve (12.) test borings_ The test.
borings were located by Empire Laboratories, Inc. from existing street
intersections using conventional chaining methods. The locations of the
test borings are shown on the Test Boring Location Plan included in
Appendix A of this report. Boring logs prepared from the field logs are
shown in Appendix A. These logs show soils encountered, location of
sampling, and ground water at the time of the exploration.
The borings were advanced with a four -inch diameter, continuous -
type, power -flight auger drill. During the drilling operations, a
geotechnic.al engineer from Empire Laboratories, Inc. was present and
made continuous observations of the soils encountered.
-1-
SITE LOCATION AND DESCRIPTION
The proposed residential site is bordered by Seneca Street. on the
west, Regency Drive on the southwest, Wake Robin Lane on the south,
proposed Troutman Parkway on the north and the Pleasant Valley and
Lake Canal on the east in southwest Fort Collins, Colorado. More
particularly, the site is described as a tract of land situate in the
Southeast 1 /4 of Section 34, Township 7 North, Range 69 West of the
Sixth P.M., City of Fort Collins, Larimer County, Colorado.
The site consists of a large vacant tract of land with gently rolling
terrain. Major drainage is slight to the east and northeast. The area is
currently vegetated with grass and weeds. The south and west portions
of the site are bordered by ditches. A large culvert is located at the
intersection of Regency Drive and Seneca Street. A large stockpile is
located at the southeast corner of the site and is approximately 100 feet
long, 25 feet wide and 5 to 10 feet in height. The northern part of the
property is bordered by an existing fence, and the eastern portion of
the property is bordered by the Pleasant Valley and Lake Canal, which
forms the east property line. A new elementary school is located to the
northwest, and a junior high school is currently under construction west
of the property. Open land is located to the north and east, and
residential areas are Located to the south.
LABORATORY TESTS AND EVALUATION
Samples obtained from the test borings were subjected to testing in
the laboratory to provide a sound basis for evaluating the physical
properties of the soils encountered. Moisture contents, dry unit
weights, unconfined compressive strenaths, water soluble sulfates, pH,
sulfides, laboratory resistivity, oxidation-reduction potential, swelling
potentials, and the Atterberg limits were determined. A summary of the
test results is included in Appendix B. Consolidation,
swell -consolidation and Hveem stabilometer characteristics were also
determined, and curves showing this data are included in Appendix B.
-2-
SOIL AND GROUND WATER CONDITIONS
The soil profile at the site consists of strata of materials arranged
in different combinations. In order of increasing depths, they are as
follows:
(1) Silty Topsoil: The majority of the area tested is overlain by a
six (6) inch layer of silty topsoil. The topsoil has been
penetrated by root growth and organic matter and should not
be used as a bearing soil or as a fill and/or backfill material.
It is recommended that the topsoil be stripped and stockpiled
for reuse in planted areas.
(2) Silty Clay: A layer of brown silty clay underlies the topsoil
and surface and extends to depths of one (1) to four and
one-half (4-1 /2) feet below the surface. The silty clay is
plastic, contains minor amounts of sand and traces of gravel
and exhibits moderate bearing characteristics in its dry to damp
natural condition. When wetted, the clay stratum exhibits
moderate to high swell potential.
(3) Sandy and/or Sandy Gravelly Silty Clay: This stratum
underlies the upper clays and extends to the bedrock below
and/or the depths explored:, The lower silty clay stratum is
red to tan, contains varying amounts of sand and gravel and
lenses of silty sand and gravel and is damp to moist in situ.
When wetted, the lower clay stratum exhibits slight to moderate
swell potential; and upon loading, consolidation occurs.
(4) Siltstone-Sandstone . Bedrock: The bedrock was encountered
below the upper clays in Borings 2 through 7 and 9 through 12
at depths of three (3) to fourteen and one-half (14-1/2) feet
below the surface and extends to greater depths. The bedrock
was encountered at relatively shallow depths of three (3) to
nine (9) feet in the southern third of the property in the area
-3-
of Borings 6 and 10 through 12. The; upper one and one-half
(1-1 /2) to two (2) feet of the bedrock is highly weathered;
however, the underlying siltstone interbedded with minor
amounts of sandstone is dense and exhibits very high bearing
characteristics. When wetted, the siltstone portion of the
bedrock stratum exhibits high swell potential.
(5) Ground Water: At the time of the investigation, free ground
water was encountered in Boring 2 at a depth of eleven (11 )
feet below the surface. No free ground water was encountered
in the remaining borings drilled at the site to the depths
explored. Water levels in this area are subject to change due
to seasonal variations, irrigation demands on and/or adjacent to
the site, and the volume of flow in the. Pleasant Valley and Lake
Canal located adjacent to the site. In addition, it is our
opinion that surface Water may percolate through the upper
subsoils and become trapped on the relatively impervious
bedrock stratum, forming a perched ground water condition.
GEOLOGY
The proposed subdivision is located in the Colorado Piedmont section
of the Great Plains physiographic province. The Colorado Piedmont,
formed during Late Tertiary and Early Quaternary time (approximately
sixty-five million (65,000,000) years ago), is a broad, erosional trench
which separates the Southern Rocky Mountains from the High Plains.
Structurally, the property lies along the western flank of the Denver
Basin. During the Late Mesozoic and Early Cenozoic Periods
(approximately seventy million (70,000,000) years ago), intense tectonic.
activity occurred, causing the uplifting of the Front Range and the
associated downwarping of the Denver Rasin to the east. Relatively flat
uplands and broad valleys characterize the present-day topography of the
Colorado Piedmont in this region. The site is underlain by the
Cretaceous Pierre Formation. The Pierre shale is overlain by alluvial
and colluvial clays and gravels of Pleistocene and/or Recent Age.
z2
Bedrock underlies the site at depths of three (3) to approximately
twenty (20) feet below the surface. The dip of the bedrock in this area
is slight and in an easterly direction. Seismicactivity in the area is
anticipated to be low; therefore, from a structural standpoint, the
property should be relatively stable. Due to the generally flat to gently
rolling nature of the property, geologic hazards due to mass movement,
such as landslides, mudflows, etc., are not anticipated on the property.
The site lies within the drainage basin of Mail Creek, which is a
tributary of Fossil Creek. Drainage of a tributary of Mail Creek is
directed along the southwest corner of the site, below Seneca Drive and
into two large concrete pipes just north of the its intersection with
Regency Drive. The 100 year flood plain of this intermittent tributary
should be established, and residential construction should be elevated
above or placed beyond the flood plain of this drainage..
RECOMMENDATIONS AND DISCUSSION
It is our understanding the site is to be developed for single-family
residential construction. Due to the topography of the site, minor site
grading of the area is anticipated. At the time of the site exploration,
the locations of the residential lots and streets were not known. The
test borings were placed to determine representative subsurface
conditions throughout the site. Recommendations for pavement
thicknesses of streets will be provided after the locations of the streets
are determined and traffic data can be obtained from the City of Fort
Collins. Pavement thicknesses for typical residential streets are
provided in this report.
Site Grading, Excavation and Utilities
Specifications pertaining to site grading are included below and in
Appendix C of this report. It is recommended that the upper six (6)
inches of topsoil penetrated by root growth and organic matter below
building, filled and paved areas he stripped and stockpiled for reuse in
planted areas. The upper six (6) inches of the subgrade below
-5-
building, paved and filled areas should be scarified and recompacted
between optimum moisture and two percent (2%) wet of optimum moisture
to a minimum of ninety-five percent (95%) of Standard ProctorDensity
ASTM D 698-78. (See Appendix C.) Finished subgrade below streets
and paved areas should be placed a minimum of three (3) feet above the
bedrock stratum, and this should be taken into account in the site
grading plan proposed for the site. If the finished street subgrade is
placed within three (3) feet of the bedrock, subdrains may be required
to intercept potential perched ground water. nue to the clayey nature
of the upper subsoils, unstable conditions may occur in the street
subgrade during construction and/or under proof_rolling. Should this
occur, stabilization may be required. The use of lime, geotextiles, pit
run, kiln dust or fly ash could be used to provide the proper
stabilization. Fill should consist of the on -site soils or imported
granular material approved by the geotechnical engineer. Fill should be
placed in uniform six (6) to eight (8) inch lifts and mechanically
compacted between optimum moisture and two percent (2%) wet of
optimum moisture to a minimum of ninety-five percent (95%) of Standard
Proctor Density ASTM D 698-78. The material stockpiled on -site should
be evaluated to determine if it is suitable for use as structural fill. If
it is determined the material is not suitable, it should be wasted from
the property or used in open and planted areas.
Bedrock encountered at the site may be used as fill material in
selected areas. Heavy-duty construction equipment equivalent to a track
mounted excavator having a gross weight of ninety thousand (90,000)
pounds or a D-8 tractor and ripper tooth may be needed to excavate the
firm bedrock. Bedrock used as fill should be broken into pieces less
than six (6) inches in diameter. Proper placement of the bedrock as fill
may be difficult, and a disc or other mixing equipment may be needed to
obtain uniform moisture and proper compaction. The bedrock should be
used in open and planted areas or in the Lower portion of fill below
paved areas.
In computing earthwork quantities, an estimated shrinkage factor
of eighteen percent (18%) to twenty-three percent (23%) may be used for
the on -site clays compacted to the above -recommended density. A
-6-