CHAPTER 7
STRUCTURES
Section 3701. (previously 3058). Manhole Construction.
(a) Manholes. The contractor shall construct manholes at the points and of the type shown on the improvement plans. All manholes shall be watertight structures with concentric cones and precast reinforced barrel sections conforming to Standard Drawing No. 13. Manholes shall have a 48-inch interior diameter for all sewers except that 60-inch interior diameter manholes are required for all trunk sewers 21 inches or larger in diameter.
(b) Manhole Bases. Concrete for the base shall be Class 2 concrete. Manhole base shall be cast in place and shall be placed on firm, undisturbed ground. If water or soft soils are present, a minimum of eight inches of three-quarter-inch crushed rock bedding shall be placed. Internal vibrators will be required for consolidation of concrete on all poured manhole bases. An impression ring shall be placed in the “wet” concrete to produce a depression for a precast manhole section. Where possible the pipe will be laid through the manhole and the top broken out to springline after the concrete in the base has set. Precast manhole base is not acceptable without written acceptance by the District, and shall not be altered in any way once delivered on site. A CVSan inspector must be notified in advance and must be present when the manhole base is poured. The manhole base shall consist of one continuous concrete pour. Water stops are required for all new manholes.
(c) Precast Manhole Sections. Precast manhole sections, conforming to Section 3209 of this Code, shall be the standard manholes for the District. Joints between concrete manhole sections and other parts including base shall be completely filled with preformed plastic joint material such as Ram-Nek. Cement mortar shall be applied at the inside and outside wall of the joint. Trim mortar smooth for interior and exterior joints. For locations with groundwater, apply external concrete joint tape wrap, Rub’R Nek six inches wide by Henry Company. Maximum allowable distance from the top of cone section to the top of manhole frame shall be 12 inches.
The interior and exterior surface of the precast manhole sections shall be coated with a concrete sealant material: Tegraproof, Xypex, bituminous material, or other cement waterproofing material approved by the District.
(d) Manhole Steps. Shall be installed only if specified or directed to by the authorized District representative.
(e) Castings. Castings shall conform to the shape, weights and dimensions shown in Standard Drawing No. 11, and Section 3203 of this Code. The frame shall be accurately set to the street grade or ground surface. Covers shall fit snugly and shall not “rock” in the frames. In paved and unpaved areas, unless specified by the authorized District representative, a concrete collar shall be poured around the frame, adjusting ring and cone as shown on Standard Drawing No. 13.
(Added, §1, Ord. 35, 04-06-59)
(Amended, §1, Ord. 52, 08-05-75)
(Amended, §2, Ord. 76, 02-12-85)
(Amended, §1, Ord. 133, 01-07-03)
(Amended, §1, Ord. 138, 07-01-05)
(Amended, §1, Ord. 150, 07-01-09)
(Amended, §1, Ord. 162, 07-01-14)
(Amended, §1, Ord. 169, 05-03-16)
(Amended, §1, Ord. 174, 11-07-17)
(Amended, §1, Ord. 183, 09-03-19)
Section 3702. (previously 3060). Manhole Protection.
Particular care must be taken to protect the manhole from damage and to keep rock, dirt and/or debris from getting into the sewer. After the sewer pipe through the manhole has been broken out and channel finished, a false bottom shall be placed over channel whenever construction work is performed at the manhole. A temporary metal plate cover, of adequate strength, close-fitting and well-secured, shall be placed over the manhole opening until the frame and cover are permanently installed, as shown in Standard Drawing No. 22.
(Added, §1, Ord. 35, 04-06-59)
(Amended, §1, Ord. 150, 07-01-09)
(Amended, §1, Ord. 162, 07-01-14)
(Amended, §1, Ord. 169, 05-03-16)
(Amended, §1, Ord. 183, 09-03-19)
Section 3703. (previously 3094). Manhole Vacuum Testing.
All sewer manholes shall be vacuum tested prior to backfill. Vacuum test procedures and requirements shall be as follows:
(a) After completion of the manhole barrels and prior to grade ring installation, all openings in the manhole are sealed with plugs and a rubber ring “donut” type plug inserted inside the opening of the cone.
(b) The vacuum test shall be performed in accordance with Standard Test Method for Concrete Sewer Manholes by Negative Air Pressure (Vacuum) Test Prior to Backfill, ASTM Designation C 1244-05a. A small vacuum pump shall be attached to a hose connected to the plug and 10 inches mercury (Hg) of vacuum applied. The vacuum line shall be closed and the vacuum pump shut down. The time shall be measured for the vacuum to drop to nine inches mercury. The manhole is acceptable if the time for the vacuum reading to drop from 10 inches Hg to nine inches Hg meets or exceeds the values listed in subsection (c) of this section. The manhole must maintain vacuum such that no greater than one inch Hg of vacuum is lost during the specified test period.
(c) The specified test period is as follows:
|
Manhole Depth (feet) |
Test Period Based On Manhole Size (seconds) |
||
|---|---|---|---|
|
48-Inch Diameter |
60-Inch Diameter |
72-Inch Diameter |
|
|
Up to 8 |
20 |
26 |
33 |
|
10 |
25 |
33 |
41 |
|
12 |
30 |
39 |
49 |
|
14 |
35 |
46 |
57 |
|
16 |
40 |
52 |
67 |
|
18 |
45 |
59 |
73 |
|
20 |
50 |
65 |
81 |
|
22 |
55 |
72 |
89 |
(d) Manholes that fail the test shall be patched as required and retested.
(e) A vacuum regulator shall be provided on the vacuum pump such that no greater than 10.5 inches Hg can be applied to the manhole during the test. All manholes that do not meet the leakage test or are unsatisfactory from visual inspection shall be repaired or replaced to the satisfaction of the District Inspection Staff.
(Added, §5, Ord. 119, 06-03-98)
(Amended, §1, Ord. 126, 02-01-00)
(Amended, §1, Ord. 133, 01-07-03)
(Amended, §1, Ord. 138, 07-01-05)
(Amended, §1, Ord. 150, 07-01-09)
(Amended, §1, Ord. 162, 07-01-14)
(Amended, §1, Ord. 169, 05-03-16)