Furnish all labor, materials, equipment and incidentals necessary for the installation of sanitary sewer manholes and frames.
A. 
The manholes shall be constructed of precast reinforced concrete manhole sections. The sections shall be a minimum of four feet in diameter and shall conform to the requirements of "Specifications for Precast Reinforced Concrete Manhole Sections," ASTM 0478.
B. 
Manhole bases shall be constructed of precast reinforced concrete. Manhole bottoms shall have a bottom at least six inches thick. The walls shall extend a minimum of six inches above the top of the highest in-flowing sewer. There shall be a minimum of five inches between the invert of lowest outfalling sewer and floor of the precast base to provide for the construction of a brick invert and bench wall within the manhole.
C. 
Openings in manhole bases of pipe connections shall utilize a flexible neoprene boot mechanically clamped to the manhole and to the pipe to provide a watertight seal which will accommodate pipe movements up to two inches radially or 22º angularily in any direction. Gaskets shall conform to requirements of ASTM C-443.
D. 
The top section shall be an eccentric conical section with thickened upper walls with the smallest inside diameter equal to 30 inches, to receive the manhole, frame and cover.
E. 
O-ring gasket for joints between manhole sections shall conform to ASTM C-443 or as specified in the drawings.
F. 
The exterior surface of all sanitary manholes shall be given two coats of coal tar epoxy such as koppers 300-M, Rust-Oleum 93-7908, or approved equal.
G. 
All castings for manhole covers and frames shall be Class 30 conforming to the ASTM Standard Specification for Gray Iron Castings, designation A48. Allowances shall be made in the patterns so that specified thickness shall not be reduced. All lids which "rock" and do not lie solid after construction is finished shall be rejected and shall be replaced by adequate lids. No plugging, burning-in, or fillings will be allowed. Covers shall fit the frames in any position.
H. 
All frames and covers shall have an H-20 (eight-ton) loading rating. The total weight of each frame and cover shall be less than 400 pounds. The opening inside diameter shall be 30 inches, and the minimum total height shall be six inches.
I. 
The cover shall have the letter "S" or the word "Sewer" in three-inch letters cast into the top surface.
J. 
The brick shall be sound, hard, and uniformly burned, consistent in shape and size, and of compact texture. Bricks shall comply with ASTM Serial Designation C32, Grade MS.
K. 
Cement mortar for manholes shall consist of one part of portland cement Type II and two parts of fine sand with water added to produce the proper consistency for the type of joint.
L. 
Nonshrinking mortar for pointing and sealing manholes shall be equal to "water plug" as manufactured by Standard Drywall Products.
A. 
All manholes shall be constructed at the locations and to the elevations and dimensions shown on the drawings. Precast reinforced concrete sections shall be set vertical with sections in true alignment. Any deviations from plans must be approved by the Town's Engineer prior to installation.
B. 
Crushed stone; base to be level.
(1) 
Crushed stone shall be placed as specified in § A175-22 herein and shall be placed 12 inches below the base of the structure. (Twelve inches of sand shall be used in areas comprised of ledge.)
(2) 
The select material below the base shall be perfectly level through the limits of the structure prior to setting it. If the base is not level, it shall be removed from the trench and the material will be regraded and recompacted using equipment. Lifting one side of the base and manually placing material underneath it will not be permitted.
C. 
Pipes entering precast sections of manholes shall be set securely in the precast opening at the correct line and grade.
D. 
The joints between concrete manhole sections shall be sealed with neoprene gaskets or by other approved means to ensure watertightness of the joints. In addition to the gaskets, both the inner and outer walls at the joints shall be mortared by an approved mortar mix.
E. 
During manhole construction, all groundwater shall be kept away from newly grouted pipe and rings or freshly laid brickwork until cement has properly set and until a watertight job is obtained. Manholes which admit groundwater after completion shall not be accepted.
F. 
All manhole frames and grates shall be set flush to existing or proposed pavement as directed by the Engineer. Frames shall be set concentric with the top of the precast section on a maximum of five courses of brick in a full bed of mortar so that the space between the top of the manhole section and bottom flange of the frame shall be completely filled and made watertight. Place a ring of mortar extending to the outer edge of the concrete section as indicated on the drawings.
G. 
Manholes shall have a brick-lined invert with shelves constructed to conform to the size of the pipe and flow. At changes in direction, the invert shall be laid out in curves of the longest radius possible, tangent to the center line of the sewer pipes. Underlayment of invert and shelf shall consist of brick masonry. Shelves shall be constructed to the elevation of the highest pipe crown and slope toward the flow channel at a minimum of one inch per foot.
A. 
All sanitary sewer manholes shall be vacuum tested. Initial test pressure shall be 10 inches Hg. Table 3 contains the specified allowances for four-foot and six-foot diameter manholes. If the pressure drop exceeds one inch prior to the allowable time, the unit shall be repaired and retested.
Table 3
Specification Time for One-Inch Hg Drop
Manhole Depth
(feet)
Test Time
(minutes)
0 to 10
2
10 to 15
2 1/2
Greater than 15
3