Download - Manhole Tech Brochured
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PRECAST CONCRETE
MANHOLES
Sustainable Stormwater Solutions
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2 MANHOLE TECHNICAL NATIONAL PRECAST CONCRETE ASSOCIATION
Why Precast Concrete .................................................. 2
Sustainable Benets o Precast Concrete ....................3
LEED Properties o Precast Concrete...........................4
Case Study ..................................................................5
Installation Procedures .................................................6
Testing Procedures .......................................................7
NPCA Plant Certication ............................................... 8
Find a Manhole Producer ..............................................8
Design Notes ................................................................ 9
Additional Resources ................................................. 10
TABLE OF CONTENTS
National Precast Concrete AssociationWith nearly 1,000 member companies, NPCA serves as the
voice o the precast concrete industry in the United States
and Canada. The industry includes a diverse mix o companies,
rom small single-plant manuacturers to multinational
vertically integrated companies that operate in many sectors o
the construction industry. NPCA provides an array o services
to these manuacturers that include technical engineeringsupport, the industrys largest certication program, saety
programming, educational courses and a suite o print and
online publications. In addition to services to members,
NPCA provides specialized technical inormation to owners,
contractors, engineers and designers on precast concrete
products.
Copyright 2012 by National Precast Concrete Association
(NPCA); all rights reserved. No part o this manual may be
reproduced in any orm without permission in writing rom the
National Precast Concrete Association.
1320 City Center Dr., Suite 200, Carmel, IN 46032
800-366-7731 precast.org
WHY PRECASTCONCRETE?Installation is EasyPrecast concrete manholes have become the construction
industrys product o choice over cast-in-place concrete,
brick and other non-concrete products or many reasons, not
the least o which is ease o installation. Precast concrete
manholes can be easily installed on demand and immediately
backlled. There is no need to wait or concrete or mortar to
cure at the job site. The degree o soil compaction around the
manhole and remaining trenches is never a problem, making
installation aster and easier. Contractors are amiliar with how
to handle precast concrete manholes and can easily install
them. Standard sealants and fexible joints are readily available
and are vital to watertightness.
Were Talking Quality Here
Because precast concrete products typically are madein a controlled environment, they exhibit high quality and
uniormity. Variables aecting quality typically ound on a job
site temperature, curing conditions, material quality and
cratsmanship are nearly eliminated in a precast plant.
Rough, Tough and Long-LastingPrecast concrete strengthens with time, while other materials
can deteriorate, experience creep and stress relaxation,
ANATOMY OF
A MANHOLE
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3 MANHOLE TECHNICAL NATIONAL PRECAST CONCRETE ASSOCIATION
lose strength and/or defect as they age. The load-carrying
capacity o precast concrete is derived rom its own structural
qualities and does not rely on the strength or quality o
the surrounding backll materials. Studies have shown
that precast concrete products can provide a service lie inexcess o 100 years. For severe service conditions, additional
design options are available that can extend the lie o the
precast concrete product. This is extremely important when
calculating lie-cycle costs or a project.
Nasty Weather? No ProblemPrecast concrete increases eciency, because weather will
not delay production o the manholes. In addition, weather
conditions at the job site do not signicantly aect the
schedule, because less time is required to install precast
compared with other construction materials, such as cast-in
place concrete or brick.
Watertight Darn RightASTM C478, Standard Specication or Precast Concrete
Manhole Sections, species the proper manuacture o
quality, watertight precast concrete manholes. Standard
watertight sealants and gaskets are available that are specially
designed or use with precast concrete, making multiple-
seam precast concrete manholes very easy to construct.
Vacuum testing is an easy means o veriying water tightness,
either in the plant or in the eld, as detailed in ASTM C1244,
Test Method or Concrete Sewer Manholes by Negative Air
Pressure (Vacuum) Test Prior to Backll.
Will Sit Tight Without Tie-DownsWith a specic gravity o 2.40 and superior rictional
resistance, precast concrete manholes resist buoyant orces
better than all other manhole materials. Fiberglass has a
specic gravity o 1.86 and HDPE has a specic gravity o
0.97, requiring the use o tie downs and ultimately increasing
project costs and installation headaches. With the many
advantages over alternative products, precast concrete
SUSTAINABLE BENEFITSOF PRECAST CONCRETE
RecyclingPrecast plants reuse ormwork, in itsel a conservationist
practice. Osite casting signicantly reduces construction
waste that would otherwise be generated on the job site.
In addition, cementitious materials used in concrete oten
contain manuacturing byproducts such as fy ash and
blast urnace slag that would otherwise nd their way to
a landll. Wastewater at the plant can be recycled or use
in manuacturing. Steel used or concrete reinorcement is
typically comprised o 95% post-consumer recycled content.
Reduced Site ImpactSince precast concrete manholes are manuactured o site
and delivered on demand, there is a signicant reduction in
truck trac, dust, noise and debris rom ormwork associated
with poured-in-place products. Because precast concrete
manhole components are modular and standardized, they
are installed in a quicker ashion and also result in reduced
construction times and energy usage, less noise and ewer
emissions rom on-site equipment.
Regional Natural MaterialsThe cement used in concrete is made rom common
natural materials such as limestone and clay. Most
cement plants rely on nearby limestone quarries, keeping
transportation distances to a minimum. Aggregates used in
the manuacturing o precast concrete manholes are also
generally extracted and manuactured regionally.
DurabilityConcrete is a very strong and durable material, which is a
signicant sustainable attribute. It will not rust, rot or burn and
has a service lie o in excess o 100 years.
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Precast concrete manholes are a smart choice or projects
applying or LEED certication. Most o the credits shown also
qualiy or additional Innovation in Design points that are tied
to exemplary perormance o the credit listed.
SITE DEVELOPMENT: PROTECT OR
RESTORE HABITAT
(Sustainable Sites Credit 5.1)
Precast concrete manholes are plant cast and are delivered
to the site ready to set so they require very minimal site
disturbance to install.
STORMWATER DESIGN: QUANTITY
CONTROL
(Sustainable Sites Credits 6.1 and 6.2)
Most stormwater management plans will require manholes
in the design to properly handle the stormwater runo.
Precast concrete manholes unction as an integral part o
any stormwater system and can be counted on to perorm
exceptionally or many decades.
CONSTRUCTION WASTE MANAGEMENT:
DIVERT 50% (75%) FROM DISPOSAL
(Materials and Resources Credits 2.1 and 2.2)Precast concrete manholes are plant-cast and are delivered to
the site ready to set, creating minimal to zero amounts o on-
site water material.
RECYCLED CONTENT: 10% (20%) (POST-
CONSUMER PLUS PRE-CONSUMER)
(Materials and Resources Credit 4.1 and 4.2)
Precast concrete manholes may contain supplementary
cementitious materials such as fy ash and blast urnace slag,
adding to the projects recycled content goals.
REGIONAL MATERIALS: 10%
(20%) EXTRACTED, PROCESSED &
MANUFACTURED REGIONALLY
(Materials and Resources Credit 5.1 and 5.2)
The vast majority o materials that go into the manuacturing
o precast concrete manholes are available within a 500-mile
radius o the precast plant.
LEED PROPERTIES OF PRECAST CONCRETE
LEED or New Construction and Major Renovation 2009 Scorecard
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When city ocials in American Fork, Utah, approved
construction o a 175-acre commercial center, a primary
concern or the citys engineers was the environmental eect
it would have on a 45-acre wetland right next door.
PEPG Engineering project engineers designed a sophisticated
stormwater runo treatment system or its new commercial
center, which would be the home or big box stores like The
Home Depot, Wal-Mart, Kohls and a 12-screen Cinemark
Theater. Since the commercial centers runo would
wash straight into the protected Mitchell Hollow Wetland
Conservation area, the challenge was more than just a
regulatory annoyance; it was a legitimate environmental
concern.
Coexisting With ConservationTo avoid the problem o purging during high fows, engineers
specied a two-stage oil and sediment separator. The two-
stage unit includes a bypass or large storm events so that
when fows exceed capacity, water runs through the unit
without disturbing accumulated sediments and oil, keeping
pollutants out o downstream waters.
The system has another eature: a large storage capacity that
incorporates two 60-inch precast concrete manholes instead
o a smaller cast-in-place vault. Since the eectiveness o
most water-scrubbing devices relies on a strict schedule o
cleanup, the separation unit provides a big advantage to the
small towns public works department. On average, the systemrequires cleaning only once a year.
The system includes three components: A primary precast
concrete manhole set in line with the storm sewer pipe, the
separator unit and a second manhole or storage.
Installation is SimpleThe basic installation is simple: Dig, set two manholes, slip
the separation unit in place and backll. Ater the excavator
digs a hole, the utility contractor places one manhole structure
in line with the storm sewer pipe to act as a catch basin and
then to the right or let to act as an overfow storage structure.Since the unit comes in both right-handed and let-handed
congurations, it oers some fexibility around other utilities
and obstacles.
The primary manhole has an outlet large enough or the
separation unit to slip into place, with two pipes dropping into
the catch basin and two outlets. Secondary pipes connect
the unit to the storage manhole, and a reducer connects the
unit to the storm sewer pipe. Gravel backll supports all the
components. Ater manhole rames bring the structures to
nished grade, dirt backll and paving complete the installation.
Precast AdvantagesAccording to Jim Schaeer, project engineer or Ames
Construction, which built most o the utilities or the American
Fork Commercial Center, it took less than a day to install each
system. Its a good thing, given that the project required about
30 manholes. This contrasts sharply with the traditional cast-
in-place system, which can take ve to seven days or each
installation when allowing or curing beore backll.
Project ProfleProject Name: American Fork Commercial Center
Owner: AFCC Limited, Salt Lake City, Utah
Engineer: PEPG Engineering, Draper, Utah
Contractors: HE Davis & Sons, Spanish Fork, Utah Ames
Construction, Salt Lake City, Utah Geneva Rock Products, North
Orem, Utah
Precast Manuacturer: Amcor Precast (a division o Oldcastle
Precast Inc.), Ogden, Utah
CASE STUDY
A Precast Concrete Stormwater Solution
A precast concrete manhole-based stormwater systemprotects the wetlands next to this commercial developmentin American Fork, Utah.
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INSTALLATION PROCEDURES
Liting ApparatusUse approved liting slings that will adequately lit the weight
o the units and that conorm to OSHA standard 29 CFR
1910.184. The use o an approved or rated spreader bar is
preerred. When liting manhole bases and risers, make sure
the chain or cable lengths are long enough to prevent contact
with tongue-and-groove area, and are kept at appropriate liting
angles. Use wooden blocks between sling and manhole wall i
necessary.
Recommended Manhole BeddingUse a minimum o 6 inches o approved bedding material
compacted to 90% proctor in an area not less than the base
area, and preerably 6 inches beyond the outside radius o
the manhole base. The area under incoming and outgoing
pipes should be treated the same way to prevent shearing o
pipes. Local ground conditions may require additional bedding
thickness, according to the engineers recommendations.
Setting Manhole BaseSet the manhole base on graded bedding according to job
specications, making sure boots or pipe openings match
design elevations. Level the top o the manhole base in both
directions.
Pipe ConnectionsFollow the manuacturers recommendations or connections
and check with the manuacturer i precast inverts are
supplied.
Flexible Boot Connections Clean the pipe surace and
inside o boot. Insert the spring line o the pipe fush withthe inside o the manhole wall or as allowed by jurisdiction,
keeping the pipe centered in the connector. Install all take-
up clamps(s) in the groove(s) i provided at the receiving end
o the connector. Tighten the clamps to the recommended
torque, which will vary depending on size and manuacturers
specications. Any grouting that will inhibit the design/
fexibility o the connector should be avoided.
Compression Type Connector Cut a -inch bevel on the
end o the pipe to be inserted into the manhole. Clean the pipe
surace and inside area o the connector. Lubricate the inside
o the connector and exterior o area o the pipe being inserted
with an approved lubricant. Center the beveled end o the pipeinto the connector. Keeping the pipe level, push the pipe into
the connector until it is fush with the inside o the manhole
wall or as required by local specications.
Mortar Joint Locate the pipe into the opening to meet
elevations. Using non-shrink mortar, completely ll voids
around the pipe. Allow proper curing time beore backlling.
Pipe Stubs Any pipe stubs installed in the manhole must be
restrained rom movement to prevent blowout resulting rom
groundwater or any testing. A minimum o a 5-oot stub length
may be required.
Joint InstallationButyl Gasket Use only manuacturer-recommended sizes
or specic diameters. Clean and inspect all tongue-and-groove
suraces. Suraces should be ree rom all dust and debris.
On tongue-up manholes, place the butyl material next to the
vertical surace o the tongue. Wrap the material completely
around the unit overlapping each end. Knead the ends together
to orm a unied splice. Make sure all protective paper is
removed. Lower the bell end o next section making sure the
steps are aligned (i applicable) into the nal position. I the bell
is up, place butyl material next to the vertical surace o the
groove and ollow the above procedure.
Confned O-Ring Clean and inspect joint suraces. Lubricate
the joint surace liberally. Lubricate the O-ring gasket
thoroughly beore placing it into the conned groove space
provided. Run a smooth, round object between the gasket and
tongue around the entire circumerence several times. Lower
the lubricated end o the next section making sure steps are
aligned into nal position. Keep the sections level/plumb while
setting to prevent rolling the gasket and breaking the bell.
Oset and Pre-Lubricated Gaskets Install according to the
manuacturers specications.
Precast Lit Hole Sealing (ull penetration)Liting holes should be sealed by inserting a rubber plug orother approved material into the hole (i supplied) and/or lling
with non-shrink mortar rom both inside and outside.
Backfll Procedure you are vacuum testing, do the test beore backlling.
Detecting leaks at this time is easy and repairs are simple.
Distribute backll around the manhole in equal proportions to
prevent tipping. Compact the ll in lits, the same as with a
standard trench procedure. Backll material should be clean
and ree o large rocks.
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Vacuum testing is a quick, sae and practical way to validate
manhole system integrity. Manhole sections can be tested at
the precast concrete plant prior to delivery or on site prior to
backlling.
Many codes and specications require that a vacuum test be
perormed ater the manhole has been installed and backlled.
Testing ater backlling provides a degree o certainty that a
watertight system has been installed. However, the major
disadvantage is the act that no industry standards exist
or vacuum testing ater the structure has been backlled.
Secondly, it is oten dicult to determine the cause or locate
and repair a system breech once the manhole has been
backlled.
The resolution to this problem is to perorm a vacuum test
beore backlling and, i necessary, ater backlling.
ASTM C1244, Standard Test Method or Concrete Sewer
Manholes by the Negative Air Pressure (Vacuum) Test Prior
to Backll, has been developed to govern the proper vacuum
testing procedure or testing concrete manholes. ASTM C1244
clearly states that a vacuum test is intended to be used as
a preliminary test to enable the installer to demonstrate the
condition o the concrete manhole prior to backll.
When utilizing ASTM C1244, a vacuum o 10 inches Hg is
drawn on the manhole ater all lit holes are plugged, and pipes
entering the manhole are temporarily plugged and securely
braced. The time is measured or the vacuum to drop to 9
inches Hg. The manhole is acceptable i the measured time
meets or exceeds the values presented in Table 1 o ASTM
C1244. I the manhole ails the initial test, it may be repaired
by an approved method until a satisactory test is obtained.
For more details on vacuum testing, please visit preast.org.
TESTING PROCEDURES
Vacuum Test Validates System Integrity
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FIND A PRECASTCONCRETE MANHOLEPRODUCERWhether you need a custom project or standard product, visit
precast.org or call (800) 366-7731 to nd the precast concrete
manuacturers in your area. The Find a Producer button on
our home page leads to a powerul search engine that will link
you to the appropriate NPCA members based on your selection
criteria.
NPCA is happy to provide the data and support that you needto incorporate the latest precast concrete products into your
design. Check the Products & Ino section o our website to
nd inormation based on product lines. Or, contact NPCA
Technical Services directly either by email at [email protected]
or by phone at (800) 366-7731.
Want to reach the precast community, or connect with
engineers, architects, speciers and regulators who have in
interest in precast concrete? Join us on Facebook (acebook.
com/nationalprecast) and plug into the community. Its a daily
discussion o all things precast.
Certiy ExcellenceFrom start to nish, the NPCA Plant
Certication Program sets the highest
standards or plant acilities, production
operations and quality control procedures.
NPCA certied plants are dedicated to
manuacturing rst-class products. To maintain
their NPCA credentials, plants must pass
periodic, on-site certication inspections.
The NPCA Plant Certication Program enables
quality-conscious agencies, architects,
engineers and users to identiy and select
high-quality precast concrete manuacturers.
At no cost to speciers, NPCA certication
prequalies manuacturers as companies
capable o superior workmanship. You save
money, because you do not need to spend
valuable time and resources inspecting aplant to ensure that its products will meet
or exceed your expectations. You also save
time when you work with certied precast plants, because
products arrive on the job site ready or installation. Material
and labor costs are kept in check, because quality control
starts beore the work order reaches the precast plant.
The Certifcation ProcessTo become an NPCA certied plant, a precast concrete
production acility must exceed a level o excellence dened
by NPCA in accordance with relevant industry standards.Plant inspections are perormed by an engineer rom an
independent, nationally accredited rm, and all certication
applicants are graded on all critical aspects o plant operation.
A standard grading schedule is used or all inspections to
ensure uniormity. Inspections are perormed during actual
plant operation.
The NPCA Certifed PlantPrecast concrete plant operators committed to excellence
seek NPCA certication. Plants committed to quality
invest the time and resources necessary to meet the high
standards demanded by the construction industry. Staed
by experienced personnel, plants complying with NPCA
guidelines practice quality assurance at every step o the
production process. These guidelines require procedures and
products to be inspected during each phase o manuacturing
to ensure compliance with rigid industry requirements. As a
result, products rom NPCA certied plants are characterized
by high quality, uniormity and consistency. Each NPCA
certied plant is also required to maintain an active plant
saety program that meets or exceeds local, state, provincial
and ederal laws and the rules and regulations o the U.S.
NPCA PLANT CERTIFICATION
Occupational Saety and Health Administration (OSHA) and
Canadian Centre or Occupational Health and Saety.
NPCA guidelines require certied plants to maintain extensive
records to veriy that materials used in the manuacturing
process conorm to appropriate specications. Work orders,
product drawings, equipment calibration records, aggregate and
concrete test records, batching reports and product inspection
reports are also required as management tools and quality
assurance aids.
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MANHOLE DESIGN NOTES Applicablestandard:ASTMC478,StandardSpecicationforPrecastReinforcedConcreteManholeSections
Typicalsizes:48,60,72,84and96-inchdiameterswithothersizesavailable.
Diameterofthemanholeistypicallybasedonthemaximumpipesizeandtheminimumstructurallegbetweenpipe
holes.
Risersectionstypicallycomeinincrementsof12inches,upto48inches.
Transitionslabsmaybeusedtoreducethemanholediameteroveralargerbasesectiontominimizecosts.
Holesinprecastmanholeconcretesectionsforinuentandeffuentpipeconnectionscanbecastduringpouring,or
cored ater the product has cured. Holes may need to be gasketed with compression or fexible type connectors as
described in ASTM C923 and C1478.
Thebasemaybepouredmonolithicallyormayhaveaseparatebase.Aninvertorowchannelcanalsobepouredintothe
base section i required.
Weldedwirereinforcingorhoopsteeliscommonlyusedinprecastconcretemanholes.Theminimumtotalwall
reinorcing area required is 0.0025 times the internal diameter in inches per vertical oot as noted in ASTM C478.
Baseandtopslabsmusthaveaminimumreinforcementof0.12sq.in./ftineachdirectionfor6i-inchslabthickness.
Jointsinmanholesectionsaredesignedtoresistpassageofsolidsoruidswhiletightenoughtopassvacuumtestingif
required. Rubber gaskets and/or preormed mastic or butyl gaskets are used to seal the joint.
Stepsareinstalledduringthemanufacturingprocess,andmustconformtorequirementsoftheOccupationalSafetyand
Health Standards, U.S. Department o Labor. Standard loads are outlined in ASTM C478 and C497.
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ADDITIONAL RESOURCESASTM A48/A48M, Standard Specication or Gray Iron CastingsASTM A185 / A185M, Standard Specication or Steel Welded Wire Reinorcement, Plain, or Concrete
ASTM A496, Specication or Steel Wire, Deormed, or Concrete Reinorcement
ASTM A497/A497M, Standard Specication or Steel Welded Wire Reinorcement, Deormed, or Concrete
ASTM A536, Standard Specication or Ductile Iron Castings
ASTM A615/A615M, Standard Specication or Deormed and Plain Carbon-Steel Bars or Concrete Reinorcement
ASTM A884, Specication or Epoxy-Coated Steel Wire and Welded Wire Reinorcement
ASTM C443, Standard Specication or Joints or Concrete Pipe and Manholes, Using Rubber Gaskets
ASTM C478, Standard Specication or Precast Reinorced Concrete Manhole Sections
ASTM C497, Standard Test Methods or Concrete Pipe, Manhole Sections, or Tile
ASTM C923, Standard Specication or Resilient Connectors Between Reinorced Concrete Manhole Structures, Pipes, and
Laterals
ASTM C990, Standard Specication or Joints or Concrete Pipe, Manholes, and Precast Box Sections Using Preormed
Flexible Joint Sealants
ASTM C1244, Test Method or Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test Prior to Backll
ASTM C1478, Specication or Storm Drain Resilient Connectors Between Reinorced Concrete Storm Sewer Structures,
Pipes, and Laterals