ORD 537 9/25/2001ORDINANCE NO. 53%
AN ORDINANCE AMENDING ORDINANCE NUMBER 464 (THE ORDINANCE), TITLED
"SUBDIVISION ORDINANCE", "CONSTRUCTION STANDARDS", APPENDIX B, SECTION B.
SANITARY SEWER SYSTEM, SUB -SECTION 2) "STANDARDS", PARAGRAPH "h."
"MANHOLES".
This section of the Ordinance shall be changed to read as follows:
h. Manholes
1. LOCATION
Manholes shall be spaced no more than four hundred (400') feet apart accept as required for
change of direction and shall be constructed in accordance with the City Of Cibolo Standard
Specifications as follows:
2. DESCRIPTION:
This item shall govern the construction of standard sanitary sewer manholes complete in
place and the materials therein, including manhole rings and covers. All plans, materials
and specifications shall be in accordance with the Texas Natural Resource Conservation
Commissions rules to include: 30 TAC 313.5, and design criteria for sewerage systems 30
TAC 317.1, 30 TAC 317.2, 31 TAC 317.3 and 30 TAC 317.13, or any revisions thereto as
applicable. All manholes shall be watertight.
a. Types: Unless approved by the City, standard sanitary sewer manholes shall be
constructed on influent or effluent pipes less than twenty four (24") inches in
diameter with precast reinforced concrete manhole sections or be monolithically
poured concrete manholes. A standard sanitary sewer manhole shall be a single
maintenance entrance cylindrical structure having a uniform internal diameter of
four feet (4'), five feet (S) or six feet (6) structure to the bottom of the diameter
adjustment section or cone. The base of the structure shall include the load
bearing portion beneath and exterior of the structure, invert channels and the fill
or bench portions adjacent to the lower sewer pipes within the structure. The
maximum vertical height of the diameter adjustment section or cone shall be
thirty-six inches (36"). Adjustment or throat rings may be used for elevation
adjustment of the manhole ring and cover. Manhole ring concrete encasement
shall be provided to attach the ring and cover to the diameter adjustment section
or cone, when required by the City.
3. MATERIALS:
a. Precast Reinforced Concrete Manhole Sections: Precast reinforced concrete
manhole sections shall conform to the requirements of ASTM Designation C-
478.
b. Monolithically Poured Concrete Manholes: A minimum of two and a maximum
of six throat rings shall be used at each manhole for adjustability. All concrete
for manholes shall conform to the provisions of "Concrete (Class "A")," of the
City governing specifications. All reinforcing steel shall conform to the
provisions of "Reinforcing Steel," of the City Specifications.
c. Mortar: Mortar shall be composed of one (1) part Portland Cement, two (2)
parts sand and sufficient water to produce a workable mixture. When used to
plaster manholes, it may be composed of one (1) part cement to three (3) parts
sand. Lime up to ten percent (10%) maybe used.
d. Manhole Rings and Covers: Standard manhole rings and covers shall be cast
iron. Covers shall contain no holes or openings. Lifting bars with slots cast
into the covers shall be provided for lifting purposes.
Watertight manhole rings and covers shall be cast iron and shall contain no
holes or openings except as required for bolts. Lifting with slots adequate for
pick insertion and cast into the covers shall be provided for lifting purposes.
Covers shall seat on a minimum 5/16 inch diameter rubber ring conforming to
the material requirements of ASTM Designation C443. The rubber gasket
shall rest in a groove cast in the ring. A minimum of four (4), 5/8 inch
diameter, stainless steel, hex head bolts shall be provided for each cover. The
four (4) boltholes in the covers shall be evenly spaced and provided with a
minimum 1-1/2 inch diameter counter sink for the bolt heads. On the fastened
and bolted position, the bolt heads shall not extend beyond the surface or the
cover. Gaskets of a size and material as approved by the City shall be provided
for the bolts to insure air and water tightness. Alignment marks shall be
provided on watertight rings and covers for proper bolt alignment.
The finished frames and covers shall have the bearing surfaces machined
ground and sets of rings and covers shall be marked in such a way that they can
be matched for assembly in the field. All covers shall have the words "Sanitary
Sewer" cast thereon.
e. Throat Rings: Adjustment throat rings shall be reinforced concrete rings having
a maximum thickness of two inches (2"). The internal diameter shall not be les:
than twenty-four inches (24"), and the width shall be a minimum of five inches
(5").
4. CONSTRUCTION: Manholes shall be constructed of materials and workmanship as
prescribed by these specifications.
a. Footings or bases of manholes shall be a minimum of six inches (6") in depth
below the bottom of the pipe.
b. All invert channels shall be constructed and shaped accurately so as to be
smooth, uniform and cause minimum resistance to flow. The bench shall be
finished smooth with a slope of one-half inch (1/2") per foot from the manhole
walls to the edges of the invert. The top half of all sewer pipes within the invert
channel or bench zone shall be removed flush to the inside manhole walls.
c. Joints on sewer pipes shall not be cast or constructed within the wall sections of
manholes.
I Concrete cradles shall not be required for new pre -cast manholes. Concrete
cradles shall be provided for all influent and effluent pipes on new monolithic
manhole and sewer pipe systems. Concrete cradles shall extend beyond the
outside walls of the manhole a minimum of thirty-six inches (36"). On new
monolithic sewer manhole and pipe systems and new pipe systems connecting to
existing manholes, pipes entering a manhole above the lowest sewer shall
project two inches (2") from the inside wall. Such pipes shall be installed with a
joint a minimum of six inches (6") and a maximum of eighteen inches (18")
from the outside manhole wall. A concrete cradle shall be provided for the pipe
extending from the manhole wall a minimum distance of thirty-six inches (36").
e. Voids between exterior pipe walls and manhole walls at all pipe connections in
manholes shall be filled with a nonshrink grout, concrete or mortar, as approved
by the City and inspected prior to backfilling.
f. Where connections to existing manholes are required, the adjacent pipe bedding
shall be prepared to proper grade, the existing manhole neatly cut and the new
pipe inserted so that the end is projecting two inches (2") from the inside wall.
The invert shall then be reshaped to properly channel new flows. Debris of any
kind shall be kept out of new or existing manholes or mains.
g. Monolithically Poured Concrete Manholes: The wall thickness of the manhole
shall not be less than six inches (P). The structure shall be poured in a manner
to produce dense, compacted walls free of honeycomb surfaces throughout the
pour. The base shall be poured monolithically with the walls to the manhole.
1. Concrete: All concrete shall conform to the provisions of "Concrete
(Class A)," of the City Specifications.
2. Reinforcing Steel: All reinforcing steel shall conform to provisions of
"Reinforcing Steel," of the City Specifications.
3. Membrane Curing Compound: All membrane curing compound shall
conform to the provisions of Membrane Curing," of the City
Specifications.
4. Base Diameter: The minimum base diameter shall be eight inches (8")
greater than the outside diameter of the manhole.
5. Cold Joints: A cold joint will be allowed should the manhole invert
depth exceed twelve (12') feet. One joint will be allowed per each 12
feet (12) of depth and that joint shall be approved by the City.
6. Backfill: No backfill shall be placed around the manhole until 24 hours
after the pour has been completed.
h. Throat rings shall be mortared between all bearing surfaces sufficient to provide
a minimum, in place, mortar thickness of one-quarter inch (1/4"). No more than
six throat rings may be used on any manhole.
i. Manhole Rine Encasement: All manhole rings shall be encased with
nonreinforced concrete as shown on the plan details or as approved by the City.
5. TESTING:
1. Concrete for manhole ring encasements shall conform to the provisions
of "Concrete (Class B)," minimum. Manhole ring encasement shall
extend six inches (6") below the top of the cone and have a minimum
width when measured at the manhole ring of one (I') foot. The surface
of the encasement shall be four and one-half inches (4-1/2") below the
top of the manhole ring.
2. Where manholes are constructed in existing streets and where directed
by the City, the exterior exposed surfaces of the ring, mortar; throat
rings and manhole surface shall be coated with a one-eighth inch (1/8")
minimum thickness of mastic or plastic prior to placement of concrete.
a. Hydrostatic Testing: Hydrostatic testing shall be conducted by plugging with
approved plugs all influent and effluent pipes in the manhole and filling the
manhole to the top of the manhole cone with water. Additional water may be
added over a 24-hour period to compensate for absorption and evaporate losses.
At the conclusion of the 24-hour saturation period the manhole shall be filled to
the top of the manhole cone and observed. A loss within a 30 min. period shall
be considered an unsuccessful test.
b. Vacuum Testm* R:
1. General. Manholes shall be tested after installation and prior to
backfilling with all connections (existing and/or proposed) in place.
Lift holes shall be plugged with an approved non -shrink grout prior to
testing. Drop connections and gas sealing connections shall be installed
prior to testing.
2. Test Procedure. The lines entering the manhole shall be temporarily
plugged with the plugs braced to prevent them from being drawn into
the manhole. The plugs shall be installed in the lines beyond drop
connections, gas sealing connections, etc. The test head shall be
inflated in accordance with the manufacturer's recommendations. A
vacuum of 10 inches of mercury shall be drawn, and the vacuum pump
will be turned off. With the valve closed, the level vacuum shall be
read after the required test time. If the drop in the level is less than I
inch of mercury (final vacuum greater than 9 inches of mercury), the
manhole will have passed the vacuum test. The required test time is
determined from Table 852-1.
3. Acceptance. Manholes will be accepted with relation to vacuum test
requirements if they meet the criteria above. Any manhole which fails
the initial test must be repaired with a non -shrink grout or other suitable
material based on the material the manhole is constructed of. Manholes
shall be repaired on the exterior surface only prior to backfilling. The
manhole shall be retested as described above until a successful test is
made. After a successful test, the temporary plugs will be removed.
4. Repairs to existing manholes. Any existing manhole which fails to pass
the vacuum test shall be closely examined by the City and the
Contractor to determine if the manhole can be repaired. Thereafter, the
Contractor shall either repair or remove and replace the manhole as
directed. The manhole shall then be
re -tested. The Owner may elect to simply remove and replace the
existing manhole with a new manhole.
PASSED, APPROVED AND ADOPTED THE 25"' DAY OF SEPTEMBER 2001.
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Charles Ruppert
Mayor
ATTEST:
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vonn�riffin
C ty Secretary