Chapter 5.80
MANHOLES
Sections:
5.80.040 Precast manhole construction.
5.80.050 Adjusting or repairing manholes.
5.80.060 Temporary covers and plugs for structures.
5.80.010 Description.
Manholes shall be installed at locations shown on the plans and in accordance with the following provisions, the special provisions and the standard drawings. [Ord. 2014-2 (Att. § 16-01).]
5.80.020 Precast manholes.
All precast manhole sections shall conform to ASTM C-478, except that Type II modified Portland cement shall be used. The design, the specifications and the name of the manufacturer of any precast manhole units shall be submitted to the District for approval prior to purchase. All precast manhole sections shall be vacuum tested at the factory prior to shipment and shall bear a stamp that the precast manhole section has passed the vacuum testing requirements specified in SD5MCC 5.80.070. [Ord. 2014-2 (Att. § 16-02).]
5.80.030 Manhole channels.
Where sewer lines pass through manholes, construction shall conform to the applicable standard drawings. Pipe shall be used as a form for the channel if the proper positions of the flexible joints can be maintained. Whether pipe or channel forms are used, after the manhole base concrete has taken a set, the channel shall be checked with the proper template. All channels shall be finished smooth with a steel trowel. [Ord. 2014-2 (Att. § 16-03).]
5.80.040 Precast manhole construction.
An approved form ring conforming to the dimensions of the precast barrel section joint shall be used to form a joint groove in the manhole base prior to setting the first barrel section. The concrete base shall be sufficiently cured to the satisfaction of the District before the first barrel section is set. All joint surfaces of precast sections and the manhole base shall be thoroughly clean prior to setting precast sections. These various sections shall be set in a Ram-Nek sealing gasket, or equal, and installed in accordance with the manufacturer’s recommendations.
Handling of barrel sections after the sealing gasket has been affixed shall be carefully controlled to avoid bumping the gasket and thus displacing it or covering it with dirt or other foreign materials. Any gaskets so disturbed shall be removed and replaced if damaged and repositioned if displaced. Care shall be taken to properly align the manhole section with the previously set section before it is lowered into position.
Use of precast manhole bases is not permitted. [Ord. 2014-2 (Att. § 16-04).]
5.80.050 Adjusting or repairing manholes.
All workmanship and materials shall conform to these standard specifications and to the standard drawings of the District. In the case of existing brick or cast-in-place concrete manholes, repair or adjustment in kind or with precast elements may be permitted upon approval of the District. Standard undamaged frames and covers shall be reinstalled unless otherwise directed by the District. Where the completed manhole throat will exceed 12 inches, adjustment shall be made by removing the upper portion of the manhole down to the first barrel section. Precast concrete barrel and cone sections shall be used to reconstruct the upper portion of the manhole in accordance with the standard drawings. The frame and cover shall be set to conform to the requirements of the individual location.
Before any work is started on adjusting or repairing a manhole, the channel inside the manhole base shall be covered with a temporary debris cover, consisting of plywood and canvas. This temporary debris cover shall be kept in place during all work, and upon completion, the canvas and the plywood shall be carefully removed from the manhole interior allowing no debris to fall or to remain in the manhole. [Ord. 2014-2 (Att. § 16-05).]
5.80.060 Temporary covers and plugs for structures.
The District must have accessibility to manholes to allow maintenance of the system at all times. In streets, avenues, intersections, lanes, any public thoroughfares involving automobile traffic, buses, trucks, etc., the permanent manhole casting and cover shall be installed on all actively used sewers and sewer mains, including manholes, where live laterals and/or the main sewer is being used. The permanent manhole, casting and cover shall be brought to the grade of the temporary asphalt. The manhole, frame and cover shall at a later date be set to grade to match the permanent grade when the final paving is being done.
Temporary steel plate covers of approved design shall only be used on inactive sewer lines during the construction in subdivisions or other areas not subject to active vehicular traffic where final grades for unfinished roadbeds have not been determined, or where approved or ordered by the District. If the sewer being constructed is actively used, the contractor shall install the permanent manhole frame and cover so the District can have access to the sewer for maintenance.
A temporary debris cover, as described in SD5MCC 5.80.050, shall be placed over the base of any existing manhole prior to beginning any adjustment or repair work. [Ord. 2014-2 (Att. § 16-06).]
5.80.070 Manhole testing.
All manholes shall be watertight. All manholes shall be successfully tested either with clean water or by vacuum testing.
(1) Water Testing of Manholes. When a manhole is to be water tested the inlet and outlet sewers shall be plugged and the water shall be brought up above the cone section so that the water level is at least three feet above the level of ground water outside the manhole. Manholes shall be watertight with zero leakage of water as tested over a 15-minute period. The contractor shall repair any and all leaks into the manhole noted during conditions of high ground water.
(2) Vacuum Testing of Manholes.
(a) Sanitary sewer manholes may be vacuum tested in lieu of water testing. Vacuum testing of manholes shall be performed twice, first prior to backfilling and then again after backfilling.
(b) Vacuum testing of manholes shall conform to the standard set forth in ASTM C-1244-93, Standard Test Method for Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test.
(c) The District representative shall be notified a minimum of two working days prior to the testing of the manholes.
(d) The contractor shall be responsible to perform the tests. The District’s representative shall be present during all tests.
(e) The contractor shall document the tests and submit this documentation to the District.
(f) Manholes shall be prepared for vacuum testing as follows:
(i) All lift holes shall be plugged.
(ii) All pipes entering the manhole shall be temporarily plugged, taking care to securely brace the pipes and plugs to prevent them from being drawn into the manhole.
(g) Vacuum testing of manholes shall be conducted as follows:
(i) The test head shall be placed at the top of the manhole in accordance with the manufacturer’s recommendations.
(ii) A vacuum of 10 inches of mercury shall be drawn on the manhole, the valve on the vacuum line of the test head closed, and the vacuum pump shut off. The time shall be measured for the vacuum to drop to nine inches of mercury.
(iii) The manhole shall pass if the time for the vacuum readings to drop from 10 inches of mercury to nine inches of mercury meets or exceeds the values indicated in Table 1.
(iv) If the manhole fails the initial test the leaks shall be located and the necessary repairs made by an approved method. The manhole shall then be retested until a satisfactory test is obtained.
(h) If the vacuum test fails, or 10 inches mercury vacuum cannot be obtained, the following procedure shall be followed to locate the leaks.
(i) Shut off vacuum pump.
(ii) Remove vacuum test plate from manhole.
(iii) Then, using a two-gallon hand pump sprayer (like a garden sprayer), spray the interior surface of the manhole with a soap and water mixture.
(iv) Begin testing.
(v) After 30 seconds, stop vacuum and remove vacuum test plate once again.
(vi) Check the inside of manhole for soapy bubbles, indicating the areas that leak.
|
Manhole Depth – Feet |
Manhole Diameter – Inches |
||
|---|---|---|---|
|
48" |
60" |
72" |
|
|
4' |
10 sec. |
13 sec. |
16 sec. |
|
8' |
20 sec. |
26 sec. |
32 sec. |
|
12' |
30 sec. |
39 sec. |
48 sec. |
|
16' |
40 sec. |
52 sec. |
64 sec. |
|
20' |
50 sec. |
65 sec. |
80 sec. |
|
24' |
60 sec. |
78 sec. |
96 sec. |
|
* |
5.0 sec. |
6.5 sec. |
8.0 sec. |
*Add “T” times for each additional two feet depth.
(The values listed above have been extrapolated from ASTM designation C-924-85.)
[Ord. 2014-2 (Att. § 16-07).]