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shall make a continuous and uniform manhole, compatible
with the tolerances given in
14.7
.
14.6.1 Joints are designed to perform in axial compression;
therefore, shear or load testing of the joint is not required.
14.7
Permissible Variations:
14.7.1
Internal Diameter—
The internal diameter of risers
and conical tops shall not vary more than 1 %.
14.7.2
Wall Thickness—
The wall thickness of risers and
conical tops shall be not less than that prescribed in the design
by more than 5 % or
6
5 mm, whichever is greater. A wall
thickness greater than that prescribed in the design shall not be
cause for rejection.
14.7.3
Height of Two Opposite Sides—
Variations in laying
heights of two opposite sides of risers or conical tops shall be
not more than 16 mm.
14.7.4
Height of Section—
The underrun in height of a riser
or conical top shall be not more than 20 mm/m of height with
a maximum of 13 mm in any one section.
14.7.5
Position of Reinforcement—
For risers or conical tops
with a 100-mm wall thickness or less, the maximum variation
in the position of reinforcement from that prescribed in
14.5
and
14.6
shall be
6
10 % of the wall thickness or
6
6 mm,
whichever is greater. For sections with a wall thickness greater
than 100 mm, the maximum variation in shall be
6
10 % of the
wall thickness or
6
16 mm, whichever is the lesser. In no case,
however, shall the cover over the reinforcement be less than 19
mm. The preceding minimum cover limitation does not apply
to the mating surfaces of the joint.
14.7.6
Area of Reinforcement—
Steel reinforcement areas
that are 0.1 mm
2
/linear m less than called for by design shall be
considered as meeting the required steel reinforcement area.
14.8
Rejection:
14.8.1 Risers and conical tops shall be subject to rejection
for failure to conform to any of the specification requirements.
In addition, an individual riser or conical top shall be subject to
rejection because of any of the following:
14.8.1.1 Fractures or cracks passing through the wall, ex-
cept for a single end crack that does not exceed the depth of the
joint.
14.8.1.2 Defects that indicate mixing and molding not in
compliance with
7.1
or surface defects indicating honey-
combed or open texture that would adversely affect the
function of the riser or conical top.
14.8.1.3 The planes of the ends are not perpendicular to the
longitudinal axis of the riser or conical top, within the limits of
permissible variations prescribed in
14.7
.
14.8.1.4 Damaged or cracked ends, where such damage
would prevent making a satisfactory joint.
14.8.1.5 Any continuous crack having a surface width of 0.3
mm, or more and extending for a length of 300 mm or more,
regardless of position in the wall.
15. Base Sections
15.1
Scope—
This section covers three types of precast
concrete base sections manufactured for use in the construction
of manholes used in sewer, drainage, and water works. The
three types of base sections are (
1
) a base with riser wall and
base slab cast monolithically as a single unit with or without
benching, (
2
) a base consisting of a riser section with a
secondary poured integral base slab, with or without benching,
and (
3
) a two-piece base consisting of a separate precast base
slab and a riser section with a sealed joint between the two. The
riser portions of the base section shall meet all the requirements
of Section
14
.
15.2
Acceptance:
15.2.1 Acceptability of base sections covered by this speci-
fication shall be determined by the results of such tests of
materials as are required by Section
4
; by compressive strength
tests on concrete cores or concrete cylinders required by
Section
8
; and by inspection of the finished product, including
amount and placement of reinforcement as prescribed by
15.4
and
15.7
, to determine conformance with the design prescribed
under this specification and its freedom from defects.
15.2.2 Unless otherwise designated by the owner at the time
of, or before, placing an order, two separate and alternate
methods of acceptance are permitted for the three types of base
sections manufacturer designs prescribed in
15.1
, in addition to
test of materials and inspection required in
15.2.1
.
15.2.2.1
Acceptance on the Basis of Proof-of-Design Test—
Acceptance of base section or base slab prescribed in
15.1
on
the basis of the results of a proof-of-design test performed in
accordance with
15.5.1
in place of submission of design
calculations and detail drawings.
15.2.2.2
Acceptance on the Basis of Rational Design—
Acceptance of base sections prescribed in
15.1
on the basis of
design calculations by rational method and detail drawings.
15.3
Design:
15.3.1 When acceptance is in accordance with
15.2.2.2
, the
basis of the rational design shall be the appropriate sections of
the latest edition of ACI 318.
15.3.2 Base slabs or integral floors shall have a minimum
thickness of 150 mm for risers up to and including 1200 mm in
diameter and 200 mm for larger diameters.
15.3.2.1 When a base section is precast monolithically with
a benched invert, the minimum concrete thickness from the
invert to the bottom of the integral base section shall be 100
mm.
15.3.3 Benched inverts cast either monolithically with the
base section or as a secondary casting in a cured base section
shall have the following minimum dimensions:
15.3.3.1 Minimum slope of 40 mm/m from the channel to
the inside diameter (ID) of manhole wall for the benching.
15.3.3.2 Minimum channel invert depth of one-half the pipe
ID.
15.3.3.3 When a channel is cast in a cured base section, the
minimum concrete thickness under the invert shall be 50 mm.
15.3.3.4 Width of channel at top of benching shall be a
minimum of the pipe ID.
15.3.3.5 Invert shall provide a positive flow between inlet to
outlet pipes.
15.3.3.6 The minimum channel centerline radius shall be
the pipe ID.
15.4
Reinforcement:
C478M − 15
7
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