MANHOLE AND PRECAST VAULT CONSTRUCTION

MANHOLE AND PRECAST VAULT CONSTRUCTION


PART 1 - GENERAL

1.1      THE REQUIREMENT

A. This Section covers the work necessary for the construction of manholes and precast vaults.  Manhole and vault details shall be as shown on the drawings.  This Section does not cover electrical manholes and vaults.

B. The  Contractor  shall  furnish  all  tools,  equipment,  materials,  and  supplies  and  shall perform all labor required to complete the work as indicated in the Contract Documents.

C. Manhole locations are fixed and cannot be moved or relocated from locations shown on the drawings to accommodate pipe manufacturing or laying.  If necessary, special lengths of pipe shall be provided to meet manhole location requirements.

D. Manholes and precast vaults shall be built without steps or ladders.  Flattop manholes shall only be used in locations specifically shown on the drawings.

E. Manhole and precast vault covers located in areas subject to vehicular traffic shall be designed for AASHTO H-20 loading.

F. All manholes connected to sewers 12 inches or larger shall have PVC liner.   New manholes shall be lined with ribbed PVC sheet, cast-in-place during manufacturing on precast shaft sections.    Concrete bases shall be lined in accordance with the Contract Documents.   Existing unlined manholes that are being repaired shall be lined in accordance with the Contract Documents.

G. Precast Manholes:  Precast manholes shall conform to the size, shape, form and details shown on the Contract Documents.  The precast cylinder units, precast concrete taper sections, and precast eccentric flat-top sections shall be designed and manufactured for AASHTO H-20 loading.   The Contractor shall submit shop drawings of all precast manholes. The minimum allowable steel shall be hoops of No. 4 wire cast into each unit sufficient for handling.  The Keylock joint between precast concrete shaft units, including the  joint  with  the  cast-in-place  concrete  base,  shall  be  filled  with  plastic  sealing compound conforming to Federal Specification SS-S-210A, to make a watertight joint. Once the shafting has settled, the outside of all joints shall then be sealed with a 6-inch- minimum wide joint wrap of EPDM base and butyl mastic except for the joint to the cast- in-place concrete base.    Sections of various heights shall be set perfectly plumb and used to bring the top of the manhole ring and cover to the required elevation.

H. Drop Manholes:  Drop manholes shall conform to the size, shape, form and details shown on the Contract Documents.   The drop inlet pipe shall be the same diameter as the intercepted sewer.

1.2      REFERENCE SPECIFICATIONS, CODES AND STANDARDS

A.         Comply  with  the  applicable  reference  specifications  as  specified  in  the  General Conditions.

B.         Comply with the current provisions of the following codes and standards.

1.         Commercial Standards

ASTM 48          Specification for Gray Iron Castings ASTM 33          Specification for Concrete Aggregates ASTM 150        Specification for Portland Cement

2.         Standard Specifications:  SSPWC Section 206 -3 Gray Iron Casting

3.         Federal Specification SS-S-210 A – Plastic Sealing Compound

1.3      SUBMITTALS

A.         Submittals shall be made in accordance with the General Conditions.

B. Shop Drawings:   The Contractor shall furnish complete shop drawings for all precast manhole sections, cast iron frames and covers, and appurtenances for review by the Engineer.

1.4      QUALITY ASSURANCE

A.         Comply  with  the  applicable  reference  specifications  as  specified  in  the  General
Conditions.

B. Inspection:   After installation, the Contractor shall demonstrate that all manholes have been properly installed, level, with tight joints, at the correct elevations and orientations, and that the backfilling has been carried out in accordance with the Contract Documents.

PART 2 - PRODUCTS

2.1      GRANULAR BASE

A. Granular  base  shall  conform  to  Section  02200.  The  thickness  of  the  granular  base material used to support concrete manhole bases shall be the same as the adjacent pipeline bedding.

2.2      CONCRETE

A. Ready-mixed, Conforming to ASTM 94, Alternate B:   The concrete class for manhole bases shall be 650-C-4000.  The concrete class for precast manhole and vault walls and top shall be 650-C-4000 and contain at least 6 sacks of cement per cubic yard. Maximum size of aggregate shall be 1.5 inches.  Slump shall be between 2 and 5 inches.

B.         All concrete, mortar, and grout used in the construction of manholes shall conform to
SSPWC Section 201. Mortar shall be Class C.

2.3      FORMS

A. Exterior exposed surfaces shall be plywood or other approved material.  Provide forms on all vertical surfaces.  Trench walls, large rock, or earth will not be approved as form material.

2.4      REINFORCING STEEL

A.         Conform to ASTM 615, Grade 60, deformed bars.

B. Reinforcement for poured-in-place concrete bases shall be #6 bars at 12-inches on center in each direction unless otherwise shown on the drawings.

C.         Reinforcement for precast sections shall conform to ASTM 478.

2.5      POURED-IN-PLACE MANHOLES

A. Poured-in-place type manholes may be used provided all details of construction are accepted by the Engineer.

2.6      PRECAST MANHOLE SECTIONS

A. Precast manhole sections shall be minimum 48 inches in diameter, conforming to ASTM C478.  Provide eccentric cones for all manholes.  Cones shall have same wall thickness and reinforcement as manhole section.  Top and bottom of all sections shall be parallel. Joints shall be Keylock with plastic sealing compound.

B. Prior to the delivery of any size of precast manhole section on the jobsite, yard tests will be conducted at the point of manufacture.   The precast sections to be tested will be selected at random from the stockpiled material, which is to be supplied for the job.  All test specimens will be mat tested, and shall meet the permeability test requirements of ASTM C14.

2.7      PRECAST BASE SECTIONS AND BASES

A. At the option of the Contractor, precast base sections or manhole bases may be used provided all details of construction are approved by the Engineer.  Base sections shall have the base slab integral with sidewalls.  Tie reinforcing steel to wall steel.

2.8      MANHOLE HOLE EXTENSIONS

A. Concrete grade rings for extensions shall be a maximum of 6 inches high and shall be approved by the Engineer before installation.

B. In general, manhole extensions will be used on all manholes in roads or streets or in other locations where a subsequent change in existing grade may be likely.  Extensions will be limited to a maximum height of 12 inches.   Finish grade for manhole covers in paved areas shall conform to finished ground or street surface level, unless otherwise directed by the Engineer.

2.9      MORTAR

A. Standard  premixed  mortar  conforming  to  ASTM C387  or  proportion  1 part  Portland cement to 2 parts clean, well-graded sand which will pass a 1/8-inch screen.  Admixtures may be used not exceeding the following percentages of weight of cement:   Hydrated lime, 10 percent; diatomaceous earth or other inert materials, 5 percent.  For the Keylock type joint, between grade rings, the consistency shall be such that excess mortar shall be forced out of the groove and support is not provided for the next precast manhole section to be placed.  Mortar mixed for longer than 30 minutes shall not be used.
2.10    PLASTIC SEALING COMPOUND

A. Preformed plastic sealing compound shall be 1-1/4-inch square beads, Kent-Seal No. 2 manufactured by Hamilton Kent Manufacturing Company, Kent, OH; Ram-Nek, manufactured by Henry Sealants, Houston, TX; or equal, meeting all requirements of Federal Specification SS-S-210A.

2.11    PRECAST CONCRETE VAULT

A. The  precast  concrete  vault  shall  be  precast  with  a  28-day,  4000-psi  minimum compressive  strength  concrete  and  designed  for  AASHTO H-20  loading.    Minimum dimensions are shown on the drawings.   Provide openings for pipes and grating as shown on the drawings.

2.12    MANHOLE FRAMES AND COVERS

A. Manhole frames and covers shall be fabricated of cast iron in the size and shape detailed on the drawings.  Castings shall be tough, close-grained gray iron, sound, smooth, clean, free from blisters, blowholes, shrinkage, cold shuts, and all defects, and shall conform to ASTM A 48, Class 30B.   Plane or grind bearing surfaces to ensure flat, true surfaces. Covers shall be true and seat within ring at all points.

B.         Frames shall have a minimum opening diameter of 36 inches.

C.         Manhole frame and cover sets of the type, size and quantity indicated on the Contract
Documents, shall be installed at the locations shown on the drawings.

D. Frames and covers shall be designed for H-20 loading.  Before leaving the foundry, all castings shall be thoroughly cleaned and subjected to a hammer inspection.  The interior surfaces of the manhole frame and cover shall be coated in the field with not less than 60 mils of coal-tar epoxy specified in Section 09800.

E. Each cover shall be ground or otherwise finished so that it will fit in its frame without rocking.  Frames and covers shall be shipped to the site in match-marked sets.  Covers shall have the word "SEWER" cast thereon in 3 inch high letters.  No other lettering shall appear on the top of the covers.

F.         Standard manhole frame and cover shall be Model A-1251 as manufactured by Alhambra
Foundry Co., Ltd., Model R-1739-A as manufactured by Neenah Foundry Co., or equal.

G. Certification:   When required by the Engineer, covers shall be tested by use of the Transverse Test and be able to sustain a minimum breaking load of 2200 pounds using a test bar measuring 1.2 inches in diameter and 21 inches long, with a distance between supports of 18 inches.   A laboratory certification containing transverse test results for each lot of castings shall be furnished by the foundry.

PART 3 - EXECUTION

3.1      EXCAVATION AND BACKFILL

A.         Conform to applicable portions of Section 02200.  Backfill around manholes shall be 1-1/2-sack cement sand slurry.

3.2      CONCRETE BASE

A. Manhole bases shall be constructed of Class 650-C-4000 concrete to the form and dimensions shown on the Contract Documents.

B. All concrete manhole bases shall be formed and poured on a granular base (6-inches minimum) having the same thickness as the bedding under the sewer on which the manhole base is being built. Place and thoroughly compact base with a mechanical or power vibrating tamper.

C. That portion of the base above the invert elevation of the sewer pipe shall be formed to provide a smooth channel section as indicated in the Contract Documents.  The radius of the channel shall be no less than the internal radius of the inlet pipe.  The forms shall be checked and approved by the Engineer for accuracy of dimensions and relative smoothness prior to pouring of the base.  If approved by the Engineer, free forming of bases may be allowed on pipelines 10 inches or smaller.  The concrete shall be vibrated while it is being poured into the form.  Channels shall vary uniformly in size and shape from inlet to outlet, if required.   The manhole base shall be poured as one monolithic pour.

D. Lateral connections, typically those 12 inches or smaller, with gas flaps where the main pipe size is less than 39 inches shall be recessed 12 inches from the main pipe to eliminate interference of the gas flap when cleaning the main pipe.

E. Construct concrete base in conformance with the details shown on the drawings.  Vibrate to densify the concrete and screed so that the first precast manhole section to be placed has a level, uniform bearing for the full circumference.

F. Form a Keylock joint in the base and install three beads of plastic sealing compound at the joint to assure watertight seal between base and manhole wall or place the first precast section of manhole hole in concrete base before concrete has set, if preferred. First section shall be properly located and plumb.

G. If material in bottom of trench is unsuitable for installation of the manhole, excavate below the flow line as directed by Engineer, and backfill to required grade with gravel.

3.3      PLACING PRECAST MANHOLE HOLE SECTIONS

A. Clean ends of sections of foreign materials.  Place two 1-1/4-inch square beads of plastic sealing compound completely around the groove of lower section.   One bead shall be centered on the outer shoulder and one at the outer corner in the groove.   Set next section in place.   In unlined manholes, fill remaining interior and exterior joint cavity completely with mortar of the proper consistency. Trowel interior and exterior surfaces smooth.  Unless noted otherwise, apply a 6” minimum width outside joint wrap, Rub’r-Nek by Henry Company, Seal Wrap by Sealing Systems, Inc., or equal, to all joints except the base section joint.

B. Prevent mortar from drying out and cure by applying an approved curing compound or comparable approved method.   Chip out and replace all cracked or defective mortar. Completed manhole shall be rigid and watertight.

3.4      MANHOLE INVERT

A. Construct manhole inverts in conformance with details shown on the drawings, and with smooth transitions to ensure an unobstructed flow through the manhole.   Remove all sharp edges or rough sections, which tend to obstruct flow.  Where a full section of pipe is laid through a manhole, saw cut and break out the top section as indicated and cover exposed edge of pipe completely with mortar.  Trowel all mortar surfaces smooth.

3.5      FLEXIBLE JOINTS

A. Furnish and install 2 each – 2-foot long pipe joints from all manhole walls.   Lay pipes entering manhole holes on firmly compacted granular base to undisturbed earth.  Base materials shall be as previously specified.

3.6      PERMANENT PLUGS

A.         Clean  interior  contact  surfaces  of  all  pipes  to  be  cut  off  or  abandoned  as  shown.
Construct concrete plugs or factory-made stoppers at the end at of all pipes 18 inches or less in diameter.  Minimum length of concrete plugs shall be 8 inches.  For pipe 21 inches and larger, the plugs may be constructed of common brick or concrete block.  Plaster the exposed face of block or brick plugs with mortar.   All plugs shall be watertight and capable of withstanding all internal and external pressures without leakage.

3.7      MANHOLE EXTENSIONS

A. Install extensions in conformance with the details shown on the drawings, and to height determined by the Engineer.   Seal grade ring joints with mortar as required for final leveling.  Seal remaining exterior joints and interior joints of unlined manholes with mortar Extensions shall be watertight.

B.         Repair lining per Subsection 3.17.

3.8      MANHOLE FRAMES AND COVERS

A. Install frames and covers on top of manhole to positively prevent all infiltration of surface or groundwater into manholes.  Frames shall be set in mortar on top of grade rings in unlined manholes.  Set frames so that tops of covers are flush with surface of adjoining pavement unless otherwise shown or directed.

B. The elevation at which manhole frames and covers are to be set shall be as directed by the Engineer in the field.   Covers shall be installed flush with traveled pavement and shoulders, 1/10-foot above the surface between the traveled way and the roadside ditch, and 18-inches above the surface in the roadside ditch, where applicable.   Flush installations are flush to 1/8-inch maximum height.

C. The frames and covers shall be cleaned of all foreign materials and to a fine appearance and fit.   All costs for installing manhole frame and cover sets in place as described herein, including all necessary concrete work, shall be included in the applicable contract price.

3.9      MANHOLE COLLARS

A. Construct a 12-inch wide Class B concrete collar around the exterior perimeter of the manhole frame and grade rings.

B.         The concrete collar shall extend down to the eccentric cone or flat-top.

C. Collars shall have a reinforcement hoop of #4 bar at the top and bottom with 3-inch clearance to earth.

3.10    MANHOLE OVER EXISTING SEWERS

A. Construct manhole over existing operating sewer lines at locations shown.   Perform necessary excavation as specified above, break into existing line, and construct manhole.

B. Maintain flow through existing sewer lines at all times, and protect new concrete and mortar work for a period of 7 days after concrete has been placed.  Advise Engineer of plans  for  diverting  sewage  flow  and  obtain  Engineer’s  approval  before  starting. Engineer’s approval will not relieve Contractor of responsibility for maintaining adequate capacity for flow at all times and adequately protecting new and existing work.

C. Construct the new base under the existing sewer and the precast sections as specified herein.

D. Break out the existing pipe within the new manhole, cover the edges with mortar, and trowel smooth.

3.11    CONNECTION TO EXISTING MANHOLE

A.         To use an existing stub, insure that lateral enters the stub at the slope of ¼-inch per foot.
Remove the plug and install new pipe in the socket.  Install gas flap inside manhole if none exists.

B. If no usable stub exists, core drill through the manhole base to make a hole 2 inches larger than the pipe bell and at the designated slope so that the pipe crown elevations match in the manhole. If the new lateral is 12 inches or smaller and the main pipe is less than 39 inches, cut a channel in the bench so that the gas flap will be recessed 12 inches from the main channel. Install the PVC turnback, position the pipe in the hole, and grout in place.  Repair the PVC liner and attach the turn back.

For  laterals  that are not at  the  proper  elevation, create a drop manhole only upon approval of the Engineer.  Penetrating the manhole riser wall directly for a lateral is not acceptable.

3.12    SPECIAL MANHOLES

A. Construct special manhole in conformance with applicable parts of these Specifications and as shown on the drawings.

3.13    PRECAST CONCRETE VAULT

A. Install precast concrete vault at the locations shown on the drawings.  Provide necessary excavation and backfill as specified herein.

3.14    VACUUM TESTING

A. Vacuum testing shall be performed for all manholes per ASTM C1224 unless otherwise noted.

3.15    MANHOLE REPAIR

A.         General

1. The Contractor shall perform all concrete, mortar, gunite, grout and lining repair; installation of new liner, frame and cover; adjustment to grade; and paving as necessary for a complete repair of manholes as indicated on the Contract Documents.   All work shall be performed without restriction or interruption of sewer flows.   Detailed plans shall be submitted by the Contractor prior to the beginning of construction, showing the type of any proposed or required bypass systems to be used.

2. It is the responsibility of the Contractor to take adequate measures to ensure that no debris is allowed to enter the sewer.   If at any time debris does enter the sewer, the Contractor shall clean the sewer to a point downstream as determined by and to the satisfaction of the Engineer.   All costs for cleaning the sewer to remove the debris that was allowed to enter the sewer shall be borne by the Contractor.  Existing rings and covers shown to be replaced shall be broken and disposed of by the Contractor in the presence of the Engineer.

B. Surface  Preparation:     All  interior  surfaces  shall  be  water  blasted  to  remove  all deteriorated brick, concrete, or any existing coating until a solid structure of brick or concrete is exposed.   All grease and attached residue shall be removed during the surface  preparation.    Water  blasting  shall  be  performed  with  a  high-pressure  water blaster with an adjustable pressure range of 5,000 to 8,000 psi.   Debris from water blasting shall not be allowed to enter the sewer.

C. Leak Stoppage:  Prior to the application of the mortar-leveling course for any liner, the Contractor shall stop all leaks in the structure.  The method for stopping the leaks shall be  the  Contractor’s option  as  approved  by  the  Engineer.    The  Owner  shall  not  be responsible for any method or procedure that fails to stop leaks.

D.         Mortar Application

1. Preparation of the existing surfaces shall be approved by the Engineer before application of the mortar-leveling course.   Mortar or gunite shall be applied to remove all surface irregularities and to provide a smooth surface on which to apply the liner.  All surfaces shall be as dry as possible prior to the installation of the liner.

2. A   mortar-leveling   course   shall   be   required   on   all   brick   manholes.      A mortar-leveling course is not required on precast concrete manholes unless indicated otherwise.

3.16    MANHOLE LINING

A.         PVC Liner

1.         PVC liner for new manholes shall be furnished and installed according to Section
06620, Plastic Liner for Concrete Surfaces and as described herein.

2. All T-lock ribs shall be oriented vertically.  Field joints in liner between precast concrete sections shall not be made until the joint mortar has been allowed to cure at least 48 hours.

3. Plastic liner for existing manholes and repairs shall be plain sheet and shall be attached to the structure.   All areas of repair shall be spark tested by the Contractor in the presence of the Engineer.  All areas of repair shall be patched by the Contractor to the satisfaction of the Engineer.

4. The liner must be continuous, seamless, free from any holes or defects, and completely  bonded  to  the  existing  structure,  and  have  returns  at  joints  with unlined surfaces.

B.         Polyurethane Lining

1. The selected polyurethane lining material shall be approved by the Engineer prior to beginning the application.   Once the coating formulation has been accepted and approved by the Engineer, it shall not be changed except by authority of the Engineer.

2. The lining shall be high build, corrosion and abrasion resistant, 100 percent polyurethane coating.   The lining shall be capable of application to 250 mils thickness in one continuous coat.  The lining system shall employ a 100 percent solids epoxy primer capable of bonding to damp concrete.

3. The coating material shall be recommended by the manufacturer for use with the following solutions and substances as specified in Section 06620, Plastic Liner for Concrete Surfaces.

4. The lining shall be colored white or cream.   The complete coating shall be impermeable to sewer gases and liquids, and shall be nonconducive to bacteria or fungus growth.   The lining shall be capable of being repaired at any time during its life with high-build, 100 percent solids, hand patching kits.

5. All interior surfaces of polyurethane-lined manholes, including grade rings and shelves, shall be coated unless indicated otherwise.  The coating shall be applied to a minimum thickness of 125 mils or as noted on the Contract Documents. Application of the lining shall be as specified by the lining manufacturer.

6.         The coating shall be continuous, seamless, and free from any holes or defects.

7. The coating Contractor shall spark test the completed lining per the applicable sections of Section 06620, Plastic Liner for Concrete Surfaces in the presence of the Resident Project Representative.   All holidays shall be repaired to the satisfaction of the Resident Project Representative and retested.

8.         Contractor shall furnish two plugs to permit measurement of the lining thickness.

9. Only those workers trained by and licensed as installers by the manufacturer shall be used.

10. The  Contractor  shall  take  all  necessary  precautions  to  prevent  the  installed coating from being damaged by equipment used in or taken through the work.

11. Upon completion of the work, all tools and excess material shall be removed and the structure shall be left in a clean and presentable condition.

12. All personnel working in the area shall wear personal protective air support equipment as recommended by the coating manufacturer.

END OF SECTION