(A) (1) Requirements. Manholes shall be sound, watertight structures, constructed as shown on the standard plans, or on the plans in the case of special structures. The type of manhole and its location is to be shown on the plans. The manhole shall be constructed to the rim elevations shown on the plans. The design, the specification and the name of the manufacturer shall be submitted to the District for approval prior to the purchase of any precast manhole units. Manholes shall be constructed without steps.
(2) Installation. Manholes shall be installed at the end of each line exceeding 150 feet; at all changes in grade, size or alignment; at all line intersections; and at distances not greater than 200 feet for curved sewers, and 400 feet for straight runs. Reverse curves between manholes are not permitted.
(3) Types of manholes. Types of manholes include the following.
(a) Brick manholes are not authorized or accepted. Brick manholes shall be replaced or lined per current District Standards when new connections are made.
(b) Standard manholes, consisting of base, riser and top, are precast reinforced concrete manholes with concentric cones, and are 48 inches in diameter for main sewers and trunk sewers.
(c) Siphon manholes shall be reinforced, cast-in-place concrete manholes.
(d) Cast-in-place concrete manholes shall be 48 inches in diameter and constructed in accordance with division (B)(4) below.
(e) Metering manholes are precast 48 inch diameter (minimum) manholes.
(B) (1) Manhole channels.
(a) Sanitary sewer pipe shall have a joint or coupling not more than two feet and not less than one foot beyond the outside wall of the manhole. Where sewer lines pass through manholes, the piping shall be laid as a whole pipe, and, after the manhole floor and walls have set, the top half of the piping inside the manhole shall be cut off and the sides mortared to form a smooth channel as shown on the standard plans.
(b) Channels through siphon manholes shall be formed or constructed to provide a channel width equal to the I.D. of the pipe from the center of the pipe to the manhole floor and shall be checked with a template.
(2) Manhole throat. See standard detail for maximum depth of manhole throat.
(3) Manhole base block. The base block shall be poured using Class “A” concrete and in accordance with the design shown on the standard plans. No precast base blocks shall be approved or accepted by the District.
(a) The concrete pour shall be made only on dry, firm undisturbed ground or on “rock ballast” placed on undisturbed ground. If the pour is on filled ground, the ground shall be compacted to a 95% relative compaction per ASTM D-1557 “Modified Proctor”. The concrete shall be placed with a continuous pour deposited in such a manner that segregation of material does not occur. Once deposited, the concrete shall be consolidated with mechanical vibrators so as to secure a dense watertight mass.
(b) An approved metal form ring shall be used so that a level keyed slot is formed in the fresh concrete to receive the precast manhole shaft section.
(c) For connection to an existing sewer main, the top half of the sewer pipe shall be removed to within one inch longitudinally of the inside wall of the manhole and the cut finished with mortar as specified by the Engineer.
(d) The width of opening at the top of base block shall be the inside diameter of the pipes in the manhole.
(e) In angle point manholes and in junction manholes, the pipes shall be joined by smooth curves, warped to conform to the lower half of the pipe. In all cases, the upper portion of the manhole channel from the mid-point of the pipes in the manhole to the top of the base block shall be constructed vertically.
(f) When the manhole channel is not completed in the original pour, it shall be finished smooth by use of mortar with per § 33.136. Before application of the mortar, the existing concrete surface shall be thoroughly cleaned and roughened to secure a firm bond. All channels shall be troweled smooth so that a smooth uninterrupted surface is achieved. The top of the base block shall be troweled to slope towards the channel at an approximate slope of one inch in six inches.
(4) Cast-in-place manholes. Cast-in-place manholes shall only be used if required by the District.
(5) Manhole shaft and base block. The manhole shaft shall be composed of precast concrete sections.
(a) Precast concrete sections shall be in accordance with the standard plans and shall conform to the requirements of ASTM Designation C-478 except that Type II or Type V Portland Cement shall be used. The cone section shall be concentric unless eccentric is allowed by the Engineer.
(b) The taper section shall be a maximum of three feet in height and taper concentrically from a 48-inch inside diameter to a 24-inch inside diameter.
(c) Unless otherwise directed by the Engineer, manholes to be installed in all proposed city and/or county streets and paved public easements will be constructed with standard cone section per standard detail sheets. In these cases, the grade rings and cast rings shall be installed after the street section has been completed. The 48-inch diameter rings shall be furnished in one-, two-, three- or four-foot sections.
(d) Joints between precast sections shall have a “Ram-Nek” flexible plastic gasket installed between the tongue and groove joint to make a watertight joint. After the shaft is in place, the joint shall be trimmed smooth with a sharp tool on the inside of the manhole.
(e) Manhole sections will be ordered without steps. Precast manhole base blocks are not allowed unless approved, in writing, by the District Engineer. When allowed by the Engineer for standard manholes, they shall have a standard pipe bell cast into the base block. Rubber boot type connections are prohibited.
(6) Drop connections.
(a) When a drop connection is shown on the plans, it shall be included as part of the manhole construction. The drop shall be made with approved fittings inside the manhole shaft as shown on the standard plans.
(b) After the manhole shaft is in place, the upper pipe run shall be constructed through the precast wall. The hole between the pipe and the precast section shall be mortared to a watertight condition.
(7) Manhole castings. Manhole frame and cover shall be composite frame and lids manufactured by GMI Composites, Inc. as shown on the standard plans of these specifications or approved equal. Cast-iron lids may only be used when directed by the District.
(a) The surface to be protected shall be clean.
(b) The manhole frame and cover shall be permanently set when so authorized by the Engineer.
(c) The frame shall be centered on the manhole shaft and laid on mortar to final grade. The mortar shall be neatly struck.
(d) The manhole cover shall bear the lettering “Sanitary Sewer”.
(8) Manhole collar. Unless otherwise specified by the Engineer, a concrete collar shall be poured around the frame and shaft so as to securely anchor the frame to the shaft. (See the standard plans.)
(9) Waterproofing manholes. See standard detail for waterproofing requirements upon completion of the manhole.
(10) Manhole liners or other methods approved by Engineer.
(a) All trunk manholes and drop manholes shall be lined with 65 mil thickness PVC liner embedded into the manhole concrete at time of pour. Standard manholes shall be lined where required by the Engineer. Liner shall be T-lock as manufactured by Ameron or approved equal. Liner shall extend from the casting to the top of the bench wall shelf.
(b) Joints in liner shall be heat welded with strips of PVC, same thickness as liner. Liner and joints shall be spark tested in the presence of the Engineer. Spark testing shall be performed at minimum 15,000 volts with a Tinker and Razor Holiday Detector or approved equal. Any holidays or pinholes shall be patched by thermal welding strips over the pinhole, and the area patched shall be retested. The manhole will not be accepted until it is holiday and pinhole free.
(11) Adjusting or repairing manholes.
(a) For repair of existing brick or cast-in-place concrete manholes, the repair or adjustment may be made utilizing precast elements upon approval by the District. Existing, undamaged frames and covers may be reinstalled unless otherwise directed by the District.
(b) Cast iron extension rings may be used for adjusting manhole covers to grade only where cast-iron manholes are existing and where the completed manhole throat will not exceed 12 inches. Adjustments shall be made by removing the upper portion of the manhole down to the first barrel section or equivalent. Precast concrete barrels and cone sections shall then be utilized to reconstruct the upper portion of the manhole in accordance with the standard detail.
(c) The channels in the base of the manhole shall be protected by a 48-inch or 60-inch diameter “umbrella” type shield prior to any work being done on the manhole. The “umbrella” shall be carefully removed, allowing no debris to fall or remain in the manhole when the repair has been completed.
(12) Connections to existing manholes.
(a) New connections to existing manholes wherein stubs have not been provided shall be made by core drilling through the walls and base, or by another acceptable method, in the presence of and as directed by the District Engineer. Sewer pipe shall be furnished and installed in manholes at the locations and in conformance with the approved plans.
(b) All stubs shall be plugged with stoppers at locations as shown on the plans. Where new construction starts at the stub of an existing manhole, the contractor shall plug the opening into the manhole prior to removing the plug or stopper from the stub. Said plug shall remain in place until the District Engineer approves the removal.
(Ord. 2019-02, passed 4-25-2019)