HomeMy WebLinkAboutFIRE STATION NO 10 MINOR SUBDIVISION - 35 90 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTr
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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
building.
Due to the swelling pressures exerted by the materials at subgrade
at the upper level, it is our opinion that the only positive solution for
construction of the slab at the upper level 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.
Subgrade below slabs on grade at the upper level should be prepared
in accordance with the recommendations discussed in the "Site Grading,
Excavation and Utilities" section of this report. If the subgrade below
slabs on grade at the upper level 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
designed for the imposed loadings and be reinforced with wire mesh
running .through the control joints. A floor drain system should be
designed for the garage slab to prevent the accumulation of water from
snow melt, wash water or other sources. The floor drain should empty
into a storm sewer, a sump and pump or other suitable drain outlet: In
addition, slabs on grade should be designed and constructed structurally
independent of bearing members.
-7-
To minimize and control shrinkage cracks which may develop in slabs
on grade, we suggest that control joints be placed every fifteen (15) to
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 the slab on grade not be poured until the building has been
enclosed and heat is available within the building area so that
slab -on -grade concrete is not placed on frozen ground. This will also
aid in proper curing of the slab concrete.
We further recommend that nonbearing partitions placed on floor
slabs at the upper level 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.
Parking and Driveway Areas
The required total thickness for the pavement structure is dependent
primarily upon the foundation soil or subgrade and upon traffic
conditions. Based on the soil conditions encountered at the site and the
type and volume of traffic assuming a fire truck having a maximum gross
weight of 64,000 pounds and using a group index of 13 as the criterion
for pavement design, the following minimum pavement thicknesses should
be provided for the pavement structure:
Passenger Car Parking
Asphalt Concrete 21"
Crushed Aggregate Base Course 8"
Total Pavement Thickness 10"
Asphalt Concrete 2"
Plant Mix Bituminous•Base Course 3"
Total Pavement Thickness 5"
-8-
Driveways and Truck Parking Areas
Asphalt Concrete 4"
Crushed Aggregate Base Course 8"
Select Subbase 10"
Total Pavement Thickness 22"
Asphalt Concrete 2"
Plant Mix Bituminous Base Course 8"
Total Pavement Thickness 10"
Subgrade below proposed paved areas should be prepared in accordance
with the recommendations discussed in the "Site Grading, Excavation and
Utilities'-' section. The surface of the subgrade should be hard,
uniform, smooth, and true to grade. To prevent the growth of weeds,
it is suggested that all subgrade under parking areas be treated with a
soil sterilant.
The select subbase should meet City of Fort Collins Class 1
specifications. The base course overlying the subgrade should consist
of a hard, durable, crushed rock or stone and filler and should have a
minimum "R" value of 80. The composite base course material should be
free from vegetable matter and lumps or balls of clay and should meet
the City of Fort Collins Class 5 or 6 Aggregate Base Course. The base
course should be placed on the subgrade at or near optimum moisture
and compacted to at least ninety-five percent (95%) of Standard Proctor
Density ASTM D 698-78. (See Appendix C.) It is important , that the
base course be shaped to grade so that proper drainage of the parking
area is obtained.
All asphalt concrete shall meet City of Fort Collins specifications and
shall be placed in accordance with these specifications.
A reasonable pavement alternate would be nonreinforced concrete
pavement. Using a modulus of subgrade reaction of one hundred (100)
pounds per square inch per inch, a design life of twenty (20) years,
and concrete with a modulus of rupture of six hundred (600) pounds per
square inch, the following minimum pavement thicknesses are
recommended:
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Passenger Car Parking
Nonreinforced Concrete - 5"
Driveways_ and Truck Parking Areas
Nonreinforced Concrete - 7"
Subgrade below the proposed pavement should be prepared in accordance
with the recommendations discussed in the "Site Grading, Excavation and
Utilities" section of this report.
Concrete used in the pavement should meet ASTM specifications,, and
aggregate should conform to ASTM C-33 specifications.. 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 suggested that
a minimum cement content of six (6) sacks be used for this .mix, It" is,
further recommended that laboratory mix designs be done to determine
the proper proportions of aggregate, cement, and water to meet this
requirement. It is essential that the concrete mix have a low
water -cement ratio, an adequate cement factor, and sufficient quantities
of entrained air. It is recommended that the subgrade be in a moist
condition at the time the concrete is placed. The pavement surface
should be free of depressions in which water may stand.
Catch basins and manhole castings should be separated from the
pavement with expansion joint material. The jointing plan should be
prepared by the contractor and/or architect and approved by the
geotechnical engineer prior to pavement. Longitudinal and transverse
joint spacing should be at regular ten (10) to thirteen (13) foot
intervals. Longitudinal and transverse contraction joints should have a
depth approximately equivalent to one-fourth (1/4) the pavement
thickness. The joints should be cut within twenty-four (24) hours of
pouring. Expansion joints should be full -depth and should only be used
to isolate fixed objects abutting or within the pavement area. Joint
openings wider than one-fourth (1/4) inch should be cleaned and sealed
before opening to traffic. A uniform, gritty final surface texture
should be provided. Curing should be obtained with uniform coverage
with white membrane curing 'compound or by seven-day coverage with
white polyethylene or waterproof paper. The completed pavement should
-10-
be closed to automobile traffic for three (3) days and to truck traffic for
seven (7) days. If paving is done during cold weather, cold weather
procedures should be used. The concrete should be protected from
freezing temperatures until it is at least ten (10) days old.
GENERAL RECOMMENDATIONS
0 Laboratory test results indicate that water soluble sulfates in
the soil are negligible, and a Type 1-11 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 structure on all
sides to give positive drainage. Ten percent (10%) for the first
ten (10) feet away from the structure is the suggested slope.
(3) Backfill placed around the interior and exterior perimeter of the
structure should be mechanically compacted in. uniform lifts.
Puddling should not be permitted as a method of compaction.
Interior backfill and exterior backfill below paved areas should
be compacted to a minimum of ninety-five percent (95%) of
Standard Proctor Density ASTM D 698-M (See Appendix C. )
Exterior backfill below planted areas should be compacted to a
minimum of ninety percent (90%) of Standard Proctor Density
ASTM D 698-78.
(4) Plumbing and utility trenches underlying slabs and paved areas
should be backfilled with an approved material compacted to at
least ninety-five percent (95%) of Standard Proctor Density
ASTM D 698-78. Puddling should not be permitted as a method
of compaction.
(5) Gutters and
downspouts
should be
designed to carry roof
runoff water
well beyond
the backfill
area.
-11-
(6) Underground sprinkling systems should be designed such that
piping is placed a minimum of five (5) feet outside the backfill
of the structure. Heads should be designed so that irrigation
water is not sprayed onto the foundation walls. These
recommendations should be taken into account in the landscape
planning.
(7) Plumbing under slabs should be eliminated wherever possible
since plumbing failures are quite frequently the source of free
water which may cause slab heave.
(8) Footing and/or grade beams sizes should be proportioned to
equalize the unit loads applied to the soil and thus minimize
differential settlements.
(9) It is recommended that compaction requirements specified herein
be verified in the field with density tests performed under the
direction of the geotechnical engineer.
(10) It is recommended that a registered professional engineer design
the substructure 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
structure or its location 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
-12-
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. be 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.
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APPENDIX C.
Suggested Minimum Specifications for Placement of Compacted
Earth Fill and/or Backfilis
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 backfill 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
disposed of by
suitable means prior to beginning preparation of the
subgrade. The
subgrade shall be scarified a minimum depth of six (6)
inches, moisture
conditioned as necessary and. compacted in a suitable
manner prior to
placement of fill material. Fill shall not be placed until
approval by the
geotechnical engineer or , his representative; and in no
case, shall fill
material be placed on frozen or unstable ground.
Subgrade which
is not stable may require the use of imported granular
material, geotex.tiles or other methods for stabilization as approved by the
geotechnical engineer.
FILL PLACEMENT
Fill material shall not be placed during unfavorable weather
conditions. Material proposed for use as fill shall be approved by the
geotechnical engineer or his representative prior to use. Proposed import
material shall be approved, by the geotechnical engineer or his
representative prior to hauling to the project site. Fill material shall be
C-2
uniformly mixed such as to preclude the formation of lenses of material
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
Empire Laboratories, Inc.
GEOTECHNICAL ENGINEERING 5 MATERIALS TESTING
February 9, 1990
Architectural Resource Group
205 South Meldrum
Fort Collins, Colorado 80521
Attention: Mr. Larry Trampe
Gentlemen:
CORPORATEOFFICE
P.O. Box 503 a 361 Na Howes
Fort Collins, Colorado 80522
(303)484-0359
FAX No. (303) 484-0454
We are pleased to submit our Report of a Geotechnical Investigation
prepared for the proposed Fire Station No. 10 to be located in south
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.
Ron L. Lindburg
Staff Engineer
Reviewed by:
Aa
Chester C. Smith, P.E.
President
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ER C.
�rF OF
nr:1i4:111a
scold OMces -
P.O. Box 16859 P.O. Box 1135 P.O. Box 1744 P.O. Box 5659
Colorado Springs, CO 80935 Longmont CO 80502 Greeley, CO 80632 Cheyenne, WY 82003
(719) 597-2116 (303) 776.3921 (303) 351-0460 (307) 632-9224
Member of Consulting Engineers Council
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 be made
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 1.556 (sand cone method) or ASTM D 2922, D
3011 (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
SCOPE
This report presents the results of a geotechnical evaluation
prepared for the proposed Fire Station No. 10 to be located at the
intersection of Vermont Drive and Timberline Road in south 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 substructure, (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 driveways
and parking areas to be constructed at the site.
SITE. EXPLORATION
The field exploration, carried out on January 31, 1990, consisted of
drilling, logging, and sampling six (6) test borings. The test borings
were located by Empire Laboratories, Inc. from existing curb lines 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
geotechnical engineer from Empire Laboratories, Inc. was present and
made continuous observations of the soils encountered.
-1-
SITE LOCATION AND DESCRIPTION
The proposed site is located at the southwest corner of the
intersection of Vermont Drive and Timberline Road in south Fort. Collins,
Colorado. More particularly, the site is described as a tract of land
situate situate in the East 1 /2 of Section 30, Township 7 North, Range
68 West of the Sixth P.M., Larimer County, Colorado..
The site consists of a relatively flat tract of land vegetated with
dense, low grass and weeds. The site exhibits generally poor surface
drainage characteristics. The property is bordered to the north by
Vermont Drive, to the east by Timberline Road and to the south by
vacant land. An entrance road to the Timberline Tech Center borders
the property to west.
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 strengths, water soluble sulfates,
swelling potentials, and the Atterberg limits were determined. A
summary of the test results is included in Appendix Be
Swell -consolidation characteristics were also determined, and curves
showing this data are included in Appendix B.
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:
A six (6) inch
layer of silty
topsoil was
encountered at
the surface of the
borings drilled
at the site.
The topsoil has
been penetrated
by root growth
and organic
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matter and should not be used as a bearing soil nor as a fill
and/or backfill material.
(2) Silty Clay: A layer of brown silty clay was encountered below
the topsoil and extends to the sandy silty clay below. The
silty clay is plastic and exhibits moderate bearing
characteristics. The damp upper portion of the clay stratum
exhibits moderate to high swell potential; while the moist
portions of the stratum exhibit slight swell potential. Upon
loading of the clay stratum, consolidation occurs.
(3) Sandy Silty Clay; This stratum was encountered at a depth of
seven (7) to eight and one-half (8-1/2) feet below the surface
and extends to the silty sand and gravel below or to the depths
explored. The sandy silty clay is plastic and exhibits low to
moderate bearing characteristics in its moist in situ condition.
When wetted, the clay stratum exhibits slight swell potential.
(4) Silty Sand and Gravel: The silty sand and gravel stratum was
encountered at a depth of twelve (12) to fourteen (14) feet
in Borings 3 and 4. The sand and gravel is poorly graded and
has generally moderate bearing characteristics.
(5) Ground Water: Free ground water was encountered at depth of
twelve and one-half (12=1 /2). to thirteen and one-half (13-1 /2)
feet below the surface in Borings 1, 2, 3 and 4 twenty-four
hours after drilling the site. Ground water levels in this area
are subject to change due to seasonal variations and irrigation
demands on and/or adjacent to the site.
RECOMMENDATIONS AND DISCUSSION
It is our understanding that a single -story, masonry structure with
slab -on -grade and full basement construction is proposed for the site.
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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 below building, filled and paved areas be stripped and
stockpiled for reuse in planted areas. The upper six (6) inches of
subgrade below should be scarified and recompacted two percent (2%)
wet of optimum moisture to at least ninety-five percent (95%) of Standard
Proctor Density ASTM D 698-78. (See Appendix C.) Additional fill
should consist of the on -.site soils or imported 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 to
two percent (2%) wet of optimum moisture to at least ninety-five percent
(95%) of Standard Proctor Density ASTM D 698-78.
All excavations should be dug on safe and stable slopes. It is
suggested that excavated slopes be on minimum grades of 1-1/2:1 or
flatter. 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.
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 building 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
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Standard Proctor Density ASTM D 698-78. Addition of moisture to
and/or drying of the subsoils may be needed for proper compaction.
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.
Fnt In`iat inn
In view of the loads transmitted by the proposed construction and
the soil conditions encountered at the site, it is recommended that the
structure be supported by conventional -type spread footings and/or
grade beams. All footings and/or grade beams should be founded on the
original, undisturbed soil. All exterior footings should be placed a
minimum of thirty (30) inches below finished grade for frost protection..
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 upper levels may
be designed for a maximum allowable bearing capacity of three thousand
(3000) pounds per square foot (dead load plus maximum Five load). To
counteract swelling pressures which will develop if the subsoils become
Wetted, all footings and/or grade beams at the upper level should be
designed for a minimum dead load of one thousand (1000) pounds per
square foot. Footings and/or grade beams founded at the basement level
may be designed for a maximum allowable bearing capacity of one
thousand two hundred fifty (1.250) pounds per square foot (dead load
plus maximum live load).
The predicted settlement under the above maximum loadings, as
determined by laboratory consolidation tests, should be less than
three -fourths (3/4) inch, generally considered to be within acceptable
tolerances.
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Basement, Dewatering System_ and Slabs on Grade
In view of the depth to ground water and/or bedrock encountered
at the site, it is our opinion the proposed basement construction is
feasible, provided the finished basement slab is placed a minimum of
three (3) feet above existing ground water or at elevation 88.5 or
above. If the finished basement slab is placed within three (3) feet of
existing ground water or below elevation 88.5; then it is recommended
that a complete dewatering system is designed and constructed for the
structure.
The dewatering 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 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 be a minimum of twelve (12) inches wide.
The top of the gravel backfill adjacent to foundation walls sho.uld 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 percent (90%) 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
system should empty into a sewer unde.rdrain 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.
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