Residential
Commercial

Manholes

 

Item No.  506
Manholes
506.1  Description
This item shall govern construction of manholes, complete in place, and the materials used therein, including excavation, installation, backfilling and surface restoration.  It shall also include furnishing and installing rings, covers, and appurtenances, as well as any pumping and drainage necessary to complete the work.  Wastewater manholes shall be ‘acceptance tested’ by the Contractor.
The Contractor shall submit descriptive information and evidence that the materials and equipment the Contractor proposes for incorporation in the Work are of the kind and quality that satisfies the specified functions and quality as specified or presented in the Drawings.  The New Braunfels Utilities Standard Products Lists (SPLs) form a part of the Specifications for the Work.  Contractors may, when appropriate, elect to use products from the SPL; however, submittal to the Engineer or designated representative hall still be required.  If the Contractor elects to use any materials from these lists, each product shall be completely and clearly identified by its corresponding SPL number, when making the product submittal.  This will expedite the review process in which the Engineer or designated representative decide whether the products meet the Contract requirements and the specific use foreseen by the Engineer or designated representative in the design of this engineered Project. 
 Items contained in the SPL cannot be substituted for items shown on the Drawings, or called for in the specifications, or specified in the Bidding Requirements, Contract Forms and Conditions of Contract, unless approved by the Engineer or designated representative. The Standard Product List current at the time of plan approval will govern.
506.2  Submittals
The submittal requirements of this specification item include:
A.    Type, size and manufacturer of manhole (diameter of water or wastewater manhole), structure (precast, cast in place; Standard, Tee, etc), and materials and equipment to be furnished (brick, concrete, seals, rings, covers, etc.)
B.    Aggregate types, gradations and physical characteristics for the Portland cement concrete mix.
C.    Proposed proportioning of materials for the mortar mix.
D.    Proposed Acceptance testing procedure and associated test equipment and materials Type structures and proposed adjustment technique (lowering, raising, lateral displacement).
E.    Proposed product for coating the interior surface of new and/or existing wastewater manholes.
Submittal of test Records is required and shall include as a minimum the following items.  The test records shall also be included as part of the Project records turned in with the acceptance package.
 
Name of the manhole manufacturer
Interior surface coating type and application method for Wastewater Manholes
Model and manufacturer of vacuum tester
Date tested/date re-tested
Passed/failed and state what was done to correct the problem
Test Method Used
Location/station of manhole
Precast/cast-in- place bottom
Any repairs made to the joints.
506.3  Materials and Components
A.  Concrete and Cement Stabilized Sand
All concrete shall conform to Standard Specification Item No. 403, "Concrete for Structures”.  The cast in place concrete shall be Class A, and the precast concrete manhole base sections, riser sections and appurtenances shall conform to the requirements of ASTM C478/C478M, “Standard Specification for Precast Reinforced Concrete Manhole” with Class I concrete.  All interior surfaces of wastewater manholes shall receive a coating by an application method acceptable to the Engineer or designated representative or shall be otherwise acceptably protected from the acidic effects of municipal wastewater.  Concrete for backfill of over-excavated areas shall be Class A or Class J as indicated on the Drawings.  Cement stabilized sand for bedding or backfilling, when indicated or required on the Drawings, shall contain 2 bags of Portland Cement per cubic yard.   The sand shall meet the requirements for "Fine Aggregate" in Standard Specification Item No. 403, "Concrete For Structures".
B.  Mortar
The mortar shall be composed of one part Portland cement, one part masonry cement (or 1/4 part hydrated lime), and sand equal to 2-1/2 to 3 times the sum of the volumes of the cements and lime used.  The sand shall meet the requirements for "Fine Aggregate" as given in Standard Specification Item No. 403 "Concrete For Structures".
C.  Reinforcement 
The reinforcing steel shall conform to the requirements of Standard Specification Item No. 406, “Reinforcing Steel”.  Secondary, non-structural steel in cast-in-place stormwater manholes may be replaced by collated fibrillated polypropylene fibers, if approved by the Engineer or designated representative.
D.  Brick
The brick for ring adjustment courses and for stormwater manholes shall be of first quality, sound, hard burned, perfectly shaped brick conforming to the requirements of ASTM C 62, Grade SW, or concrete brick meeting the requirements of ASTM C 55, Grade N-1.
E.  Rings and Covers
Rings and covers shall conform to the requirements of Standard Specification Item No. 503, “Frames, Grates, Rings and Covers”. 
1.  Replacement Rings and Covers, 24 in. Diameter Lids.
 This ring and cover shall be used for the replacement of broken rings and covers, minor manhole adjustment, or as otherwise directed by the Engineer or designated representative.
2.  Rings and Covers, 32 in. Diameter Lids.
This ring and cover shall be used for all new manhole construction, except as otherwise directed by the Engineer or designated representative.
F.  Bulkheads.
Bulkheads shall meet the requirements of Standard Specification Item No. 507 “Bulkheads”
G.  Precast Base Sections, Riser Sections, and Cones.
Precast concrete base sections, riser sections, and cones shall conform to the requirements of ASTM C 478.  The width of the invert shall be specifically sized for the connecting pipes.  Inverts shall be “U” shaped with a minimum depth of three fourths of the largest pipe diameter.  The invert shall have a minimum difference of 0.10 feet between the inlet and outlet.  Where lines enter the manhole up to 24 inches above the flowline of the outlet, the invert shall be filleted to prevent splashing and solids deposition.  A drop pipe shall be provided for a sewer entering a manhole at more than 24 inches above the flowline of the outlet.
 Joints for wastewater base sections, riser sections, and cones shall conform to the requirements of ASTM C 443.  Precast bases for 48 inch inside diameter manholes shall have preformed inverts.  Inserts acceptable to the Engineer or designated representative shall be embedded in the concrete wall of the manhole sections to facilitate handling; however, through-wall holes for lifting will not be permitted.  Any voids between the pipe and boot shall be filled to the springline with a product recommended by the manhole manufacturer to prevent solids collection.
H.  Precast Junction Boxes.
Precast junction boxes shall be allowed only where indicated on the Drawings or acceptable to the Engineer or designated representative.  Joints for wastewater junction boxes shall conform to the requirements of ASTM C 443.
I.    Pipe-to-Manhole/Junction Box Assemblies
Precast bases and precast junction boxes shall have flexible, resilient and non-corrosive boot connectors or ring waterstops acceptable to the Engineer or designated representative conforming to the requirements of ASTM C 923 on all wastewater pipe connections. 
J.   Precast Flat-Slab Transition/Junction Box Lids.
Precast slab transitions and lids shall be designed to safely resist pressures resulting from loads which might result from any combination of forces imposed by an HS-20 loading as defined by the American Association of State Highway and Transportation Officials (AASHTO).  The joints of precast slab transitions and of lids for wastewater applications shall conform to the requirements of ASTM C443.
K.  Precast-Prefabricated Tee Manholes.
Tee manholes shall be allowed only where indicated on the Drawings or as directed by the Engineer or designated representative.  The main pipe section shall conform to the requirements of New Braunfels Utilities Standard Specification Item No. 510, “Pipe”.  The vertical manhole portion (tee) above the main pipe shall conform to the requirements of the precast components.  
The manhole tee shall have a minimum inside diameter of 48 inches and shall rise vertically centered or tangent to the main pipe, as indicated on the Drawings or as directed by the Engineer or designated representative.  An access hole less than 48-inches in diameter shall be cut into the main pipe to allow a ledge for support of access ladders.  Unless otherwise specified on the Drawings, the main pipe portion of the tee manhole shall be paid subsidiary to the unit tee manhole price.
L.   Precast Grade Rings 
Rings shall be reinforced Class A or I concrete.
1.  Precast Grade Rings, 24-1/2 inches Inside Diameter:
This adjustment ring shall be used only for adjusting existing manholes with 24 inch lids and for Wastewater Access Device.  Inside to outside diameter dimension of ring shall be 6 inches with a thickness of 3 inches to 6 inches.
2.  Precast Grade Rings, 35 inches Inside Diameter: 
This adjustment ring shall be used for all new manhole construction with 32 inches lids.  Inside to outside diameter dimension of ring shall be 6 inches with a thickness of 4 inches to 6 inches.
M.  New Manhole Construction and Minor Manhole Adjustment: 
New manhole construction and minor manhole adjustments shall be performed as indicated on Standard Detail 533, “New Manhole Construction and Minor Manhole Adjustment”, and shall consist of adding precast reinforced concrete rings to adjust the manhole to final grade.
For new manhole construction, the maximum vertical allowable ring adjustment, including the depth of the ring casting, shall be limited to 18 inches.  For adjustments of existing manholes that fall within the limits of overlay and street reconstruction projects, the maximum vertical allowable, including the depth of the ring casting, shall be limited to two feet.  All other existing manholes shall have a maximum allowable ring adjustment, including the depth of the ring casting, of one foot.  Any adjustment that will exceed these requirements shall be accomplished as indicated on Standard Detail 321, "Major Manhole Adjustment" and as described below in subsection (N).  All manholes not located in paved areas shall have bolted covers.
N.  Major Manhole Adjustment:  
Any adjustment that exceeds the requirements of subsection (M) Minor Manhole Adjustments, shall be accomplished as indicated on Standard Detail 321, “Major Manhole Adjustment”, and shall consist of any combination of removing the concrete rings, and/or the manhole cone section, and/or the straight riser section of the manhole in order to bring the manhole to final grade.  All manholes not located in paved areas shall have bolted covers.
O. Waterproofing Joint Materials.
O-rings and wedge seals for the joints of all wastewater manholes, and for stormwater manholes when indicated on the Drawings, shall conform to the requirements of ASTM C443.  Cold applied preformed plastic gaskets for stormwater manholes shall be as specified in Standard Specification Item No. 510, “Pipe”.  The connections between reinforced concrete wastewater manhole structures and pipes shall meet the requirements of ASTM C923.
P.   Interior Surface Coatings for Wastewater Manholes
The interior surfaces of all wastewater manholes shall be coated with a product as specified on the Drawings, designated in writing by the Engineer or designated representative or included on the approved Standard Products List (SPL).
Q.  Abandonment of Existing Manholes
When designated on the Drawings for abandonment, existing manholes shall be removed to a level not less than four feet below grade. The inlets and outlets shall be securely plugged and the structure filled with material in accordance with Standard Detail 340 or as directed by the Engineer or designated representative.
506.4 Construction
All manholes shall have a minimum inside diameter of 48 inches.  Manhole base section or junction box dimension shall be appropriately increased to accommodate all converging pipe.  A minimum horizontal clearance of 12 inches shall be maintained between adjacent pipes.  Pipe ends within the base section or junction box walls shall not be relied upon to support overlying manhole dead and live load weights.  All wastewater branch connections to new or existing mains shall be made at manholes with the influent pipe crown installed at the elevation of the effluent pipe crown.  Where lines enter the manhole up to 24 inches above the flowline of the outlet, the invert shall be sloped upward to receive the flow, thus preventing splashing or solids deposition. Where the springline of an influent pipe is 24 inches  or more above the springline of the effluent pipe, a drop manhole shall be used.  Construction of extensions to existing systems shall require placement of bulkheads at locations indicated or directed by the Engineer or designated representative.  Unless otherwise indicated on the Drawings; wastewater manholes shall have concentric cones, except on manholes over large mains where an eccentric cone shall be situated to provide access to an invert ledge.  Eccentric cones may be used where conflicts with other utilities dictate.  Flat-slab tops may be used where clearance problems exist [see 506.3(J) above].
 
Manholes shall be founded at the established elevations on uniformly stable subgrade.  Unstable subgrade shall be over-excavated a minimum of 12 inches (and replaced with a material acceptable to the Engineer or designated representative.  Precast base units shall be founded and leveled on a 6 inch coarse aggregate bedding.  A pipe section with a prefabricated tee manhole and half the length of the adjoining pipe sections on each side shall be founded on a minimum of 6 inch unreinforced Class A concrete (Standard Specification Item No. 403, “Concrete For Structures).  The cast-in-place concrete cradle shall be placed against undisturbed trench walls up to the pipe's springline.
All adjustments shall be completed prior to the placement of the final surface.
Manhole components to be reused shall be carefully removed and the contact areas shall be cleaned of all mortar, concrete, grease and sealing compounds.  Any items broken in the process of removal and cleaning shall be replaced in kind by the Contractor at its expense.
If the adjustment involves lowering the top of a manhole, a sufficient depth of precast concrete rings or brick courses shall be removed to permit reconstruction.  The mortar shall be cleaned from the top surface remaining in place and from all brick or concrete rings to be reused and the manhole rebuilt to the required elevation.  The manhole ring and cover shall then be installed with the top surface conforming to the proposed grade.
If the adjustment involves raising the elevation of the top of the manhole in accordance with 506.3 (M), "New Manhole Construction and Minor Manhole Adjustment", the top of brick or concrete ring shall be cleaned and built up vertically to the new elevation, using new or salvaged concrete rings or bricks and the ring and cover installed with the top surface conforming to the proposed grade.
Cast-in-place foundations shall have a minimum depth of 12 inches at the invert flowline. The widths of all manhole inverts shall be specifically sized for the connecting pipes.  Inverts shall be “U” shaped with a minimum depth of three fourths of the largest pipe diameter.  The invert shall have a minimum fall of 0.10 of a foot between the inlet and outlet.  The lowermost riser section may be set in the Portland cement concrete, while still green, after which the foundation shall be cured a minimum of 24 hours prior to proceeding with construction of the manhole up to 12 feet in depth.  The foundation shall be cured an additional 24 hours prior to continuing construction above the 12 foot level.  Manhole depth shall be measured from the invert flowline to the finish surface elevation.  
Wastewater manholes having cast in place foundations may be constructed over existing wastewater pipes, except polyvinyl chloride (PVC), and the top half of the pipe removed to facilitate invert construction.  The manhole bottom shall rise from the springline elevation of the pipe, approximately one inch for each 12 inches of run (8%).  Wastewater manholes with lines larger than 18 inches shall require precast bases; manholes constructed over in-service mains however, may be built on cast-in-place foundations if the flow cannot be interrupted.  Precast and cast-in-place wastewater junction boxes shall be allowed only where indicated on the Drawings or acceptable to the Engineer or designated representative.  The floors of stormwater manholes also, shall rise outwardly from the springline on a slope of 1:12 (8%).
Wastewater lines, except reinforced concrete pipe, set in cast-in-place foundations, shall require a waterstop seal or gasket acceptable to the Engineer or designated representative around the outside perimeter of the pipe.  It shall be approximately centered under the manhole section wall.
Cast-in-place stormwater manholes, junction boxes and flat-slab transitions shall be reinforced, Class A concrete (Standard Specification Item No. 403, "Concrete for Structures").  All structural concrete work shall conform to Standard Specification Item No. 410, “Concrete Structures”.  Forms will be required for all cast-in-place walls above the foundation.  Where the surrounding material can be trimmed to a smooth vertical face, outside forms may be omitted.
Backfilling for manholes shall conform to the density requirements of Special Specification Item No. 510, “Pipe”.  Manhole construction in roadways may be staged to facilitate base construction.  Manholes constructed to interim elevations shall be covered with steel plates of sufficient thickness to support vehicular traffic.  Steel plates on wastewater manholes shall be set in mortar to minimize inflow.  Manholes shall be completed to finish elevation prior to placement of the roadway's finish surface.  The excavation for completion of manhole construction shall be backfilled with cement stabilized sand with 2 sacks of cement per cubic yard up to the bottom of Portland Cement pavement slabs or to within 2 inches of finish elevation of asphaltic concrete pavements.  The cement stabilized sand shall be a minimum of 12 inches thick. 
After rings and covers are set to grade, the inside and outside of the concrete rings shall be wiped with mortar so placed as to form a durable water-tight joint smooth and even with the manhole cone section.  No grouting shall be performed when the atmospheric temperature is at or below 40°F (5oC), and when necessary, because of a sudden drop in temperature, joints shall be protected against freezing for at least 24 hours.
506.5  Acceptance Testing of Wastewater Manholes:
Manholes shall be tested separately and independently of the wastewater lines.  
A .  Test by the Vacuum Method:
A vacuum test shall be performed by the Contractor prior to backfilling those manholes that fall within the right-of-way that require detouring of vehicular traffic.  A second vacuum test will not be required after backfilling and compaction is complete unless there is evidence that the manhole has been damaged or disturbed subsequent to the initial vacuum test.
For manhole installations which do not require detouring of vehicular traffic, the vacuum method is recommended and may be used by the Contractor prior to backfilling the manhole to insure proper installation so that defects may be located and repaired; however, a vacuum test shall be performed after backfilling, and compaction are complete.  Testing after backfill and compaction are complete will be the basis for acceptance of the manhole.
1.  Equipment: 
a)   The manhole vacuum tester shall be a device approved for use by the Engineer or designated representative.
b)   Pipe sealing plugs shall have a load resisting capacity equal to or greater than that required for the size of the connected pipe to be sealed.
 
2    Procedures - applicable to new 4'-0" diameter manholes.
a)   Manhole section interiors shall be carefully inspected; units found to have through-wall lift holes, or any penetration of the interior surface by inserts provided to facilitate handling, will not be accepted.  Coating shall be applied after the testing unless coating is applied before installation or unless it is applied at the factory.  All lift holes and exterior joints shall be plugged with an acceptable non-shrink grout.  No grout shall be placed in horizontal joints.
b)   After cleaning the interior surfaces of the manhole, the Contractor shall place and inflate pneumatic plugs in all of the connecting pipes to isolate the manhole; sealing pressure within the plugs shall be as recommended by the plug manufacturer.  Plugs and the ends of pipes connected by flexible boots-shall be blocked to prevent their movement during the vacuum test. 
c).  The vacuum test head shall be placed on the top of the cone section or, inside of the top of the manhole cone section, and the compression seal band inflated to the pressure recommended by its manufacturer.  The vacuum pump shall be connected to the outlet port with the valve open.  When a vacuum of 10 inches of mercury [(-5 psig) has been attained, the valve shall be closed and the time noted.  Tampering with the test equipment will not be allowed.
d)  The manhole shall have passed the test if the vacuum does not drop below 9 inches of mercury [(-4.5 psig) within three (3) minutes of the time the valve was closed.  The actual vacuum shall be recorded at the end of the three (3) minutes during which the valve was closed.
e). When the standard vacuum test cannot be performed because of design or material constraints (examples: T-Type manholes, T-Lock Liners, or other reasons acceptable to the Engineer or designated representative), testing of individual joints shall be performed as directed by the Engineer or designated representative.
 B.  Test by the Exfiltration Method: 
At the discretion of the Engineer or designated representative, the Contractor may substitute the Exfiltration Method of testing for the Vacuum test described in Section 506.5. A above.  This method may only be used when ground water is not present.  If ground water is present a Vacuum Test shall be used unless otherwise directed by the Engineer or designated representative.  All backfilling and compaction shall be completed prior to the commencement of testing.
The procedures for the test shall include the following:
1.     Manhole section interiors shall be carefully inspected; units found to have through-wall lift holes, or any penetration of the interior surface by inserts provided to facilitate handling, will not be accepted.  Coating shall be applied after the testing unless coating is applied before field assembly, or at the factory.  All lift holes and exterior joints shall be plugged with an acceptable non-shrink grout.  No grout shall be placed in horizontal joints.
2.     After cleaning the interior surface of the manhole, the Contractor shall place and inflate pneumatic plugs in all of the connecting pipes to isolate the manhole; sealing pressure within the plugs shall be as recommended by the plug manufacturer. 
3.     Concrete manholes shall be filled with water or otherwise thoroughly wetted for a period of 24 hours prior to testing.
4.     At the start of the test, the manhole shall be filled to the top with water.  The test time shall be 1 hour (60 minutes).  The Construction Inspector must be present for observation during the entire time of the test.  Permissible loss of water in the 1 hour test time is 0.025 gallons per diameter foot, per foot of manhole depth. For a 4 foot diameter manhole, this quantity converts to a maximum permissible drop in the water level (from the top of the manhole cone) of 0.05 inches per foot of manhole depth or 0.5 inches for a 10 foot deep manhole.
C.  Failure to Pass the Test - Records of Tests.
If the manhole fails to pass the initial test method as described in (A) Test by the Vacuum Method and, if allowed, (B) Test by the Exfiltration Method, or if visible groundwater leakage into the manhole is observed, the Contractor shall locate the leak, if necessary by disassembly of the manhole.  The Contractor shall check the gaskets and replace them if necessary.  The Contractor may re-lubricate the joints and re-assemble the manhole, or the Contractor may install an acceptable exterior joint sealing product on all joints and then retest the manhole.  If any manhole fails the vacuum and/or exfiltration test twice, the Contractor shall consider replacing that manhole.  If the Contractor chooses to attempt to repair that manhole, the manhole must be retested until it passes.  In no case shall cold applied preformed plastic gaskets be used for repair.  Records of all manhole testing shall be made available to the Engineer or designated representative at the close of each working day, or as otherwise directed by the Engineer or designated representative.  Any damaged or visually defective products, or any products out of acceptable tolerance shall be removed from the site.
D. Inspection.
The Engineer or designated representative shall make a visual inspection of each manhole after it has passed the testing requirements and is considered to be in its final condition.  The inspection shall determine the completeness of the manhole; any defects shall be corrected to the satisfaction of Engineer or designated representative.
506.6 Measurement:
All junction boxes and manholes of the type indicated shall be measured as units complete in place.
New manholes constructed to interim elevations to facilitate stage construction shall be measured as one unit regardless of the number of interim elevations constructed.  All labor, materials and other expenses necessary for the stage construction shall be considered subsidiary to the completed unit.  Abandonment of existing manholes shall be considered subsidiary to the completed unit, unless separate Pay Item is indicated on the Drawings and identified in Standard Contract Bid Form.
 
506.7 Payment:
Payment for completed junction boxes and manholes of the type indicated shall be made at the unit bid price for each.  The unit bid price shall include all labor, equipment, materials, time and incidentals necessary to complete the work. When indicated in the Drawings, abandonment of existing manholes shall be made at the unit price for abandonment.
 
Pay Item:                                  New Manhole Construction, ___ Dia.                  Per Each
Pay Item:                                  Special Manhole, ___ Dia.                                   Per Each
Pay Item:                                  Drop Manhole, ___ Dia.                                       Per Each
Pay Item:                                  Centered Tee Manhole, __ Dia. x ___ Dia.         Per Each
Pay Item:                                  Tangent Tee Manhole, ___ Dia. x ___ Dia.         Per Each
Pay Item:                                  Junction Box, ___ Ft x ___ Ft                              Per Each
Pay Item:                                  Major Manhole Adjustment, ___ Dia.                   Per Each
Pay Item:                                  Minor Manhole Adjustment, ___ Dia.                   Per Each
Pay Item:                                  Abandonment of existing Manholes:                   Per Each
 
End