Township of Boonton, NJ Manholes

Excavation and backfill. Excavation and backfill for manholes shall include the removal and replacing of all materials necessary for the proper construction of manholes. Excavation and backfill shall conform to the requirements for such work covered in Article IV of this Part 2.

Construction. Manholes shall conform with the typical manhole detail accompanying these specifications. Manholes shall be circular, with an inside diameter of four feet at the bottom. The walls shall be brought up vertically to approximately two feet from the top, shall then gradually decrease the diameter of the manhole and shall be of proper dimension to receive the manhole frame and cover.

Walls.

(1)

Manhole walls may be constructed of precast portland cement concrete block of proper radius, conforming to the New Jersey State Highway Standard Specification of 1961 (5.3.2), and shall be as made by the Multiplex Concrete Company or an approved equal.

(2)

All joints between blocks shall be completely filled with cement mortar consisting of one part portland cement and two parts sand. Joints shall be made to produce a smooth and uniform surface. The outside and inside surface of each manhole shall be plastered 1/2 inch thick and troweled smooth with cement mortar of the same consistency. The outside plastered surface shall be painted with one seal coat of coal tar or asphalt. The manhole may be made of poured concrete, subject to approval by the Engineer.

Manhole bottom. Upon completion for excavation of the standard manhole, six inches of crushed stone will be placed prior to placement of the concrete. Manhole bottoms shall be 1.3.5 concrete of dimensions as shown on the drawing. Concrete channels shall be formed in the bottom with a cross section of the exact shape of the sewer invert as indicated on the drawing. Channels shall have a minimum depth of 2/3 the sewer diameter, shall slope to the outlet and shall have as smooth a surface as possible. Where stubs at manholes are herein specified, channels shall be formed to connect with stubs. The surfaces of the bottom shall slope one inch to the channels.

Precast manholes. The contractor's attention is directed to the fact that primary specifications under this item are for manholes to be constructed of solid concrete block units; however, precast pipe sections specially designed for manhole construction shall be permitted. Manholes shall conform with the standard manhole details as shown on the standard detail and shall consist of a Class 3500 precast concrete base and precast barrel and eccentric cone sections. Precast manhole sections shall be tongue-and-groove-type, circular and conical reinforced concrete pipe units. They shall conform with the requirements of ASTM Specifications C-76-60T, Class IV, except wherein such specifications cannot be applied to conical sections. Lifting holes will not be permitted. Manhole steps as described herein shall be cast in. No exposed reinforcing steel shall be allowed on any face of precast manhole sections. A groove shall be formed in the precast base to receive the tongue of the manhole barrel. Joints shall be tongue and groove and be provided with a continuous rubber ring gasket, free from pits or other imperfections. When installed, the ring shall be enclosed and compressed continuously on all sides.

Brick collars. When necessary to bring the manhole frame to proper grade, brick collars will be used. Brick collars shall be laid to the thickness and dimensions shown on the drawings. All brick shall be thoroughly wet before laying and shall be laid in a full bed and joint of mortar. Joints shall be 1/4 inch on the interior face and shall be struck smooth with the interior face. Bricks shall be laid as headers with joints broken between courses, and the finished collar shall be plastered on the outside with cement mortar as shown and shall be painted with two coats of thick bituminous waterproof material.

Steps. Each manhole shall have aluminum steps, projecting six inches into the manhole, and shall extend through the wall. The steps shall be of the type called for on the manhole details.

Cover and frame. The manholes shall have a cover and frame as specified on the details. Frames shall be well bedded in mortar, making a watertight joint, and shall be adjusted so that the rim is approximately 1/4 inch above finished grade. The cover and frame shall have a shop coat of asphaltic pitch and shall have a field coat of similar paint after the frame is set in final position.

Watertightness. Each manhole shall be absolutely watertight. Manholes that are not watertight will not be accepted. Plastering on top of defective joints to correct leaky conditions will not be permitted. The connection of the sewer pipe to the manhole barrel shall be thoroughly sealed with nonshrinking mortar and, when mortar has set, shall be thoroughly painted with two coats of asphaltic waterproof material suitable for application on a wet or damp surface.