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1.0
General
This section shall outline the scope of work, materials and equipment
required for the rehabilitation of existing sanitary sewer manholes,
eliminating infiltration and restoring structural integrity from within
the existing manhole.
2.0
Sequence
of Events
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A.
Clean surface by high-pressure water blasting. |
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B.
Eliminate all active infiltration prior to form setup. |
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C.
Internal Forming System set-up. |
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D.
Placement of High Strength Ready Mixed Concrete. |
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E.
Adequate curing. |
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F.
Form removal and inspection |
3.0
Equipment
A ABS Plastic interior forming system for placing a
new structurally sound wall within a existing manhole which conforms to
the inside dimensions and irregular shapes.
(See specifications for Forming System.)
4.0
Rehabilitation Procedure
This specification shall govern all work necessary
to rehabilitate an existing manhole.
4.1
Interior Manhole Rehabilitation
The floor and interior walls of the manhole shall
be thoroughly cleaned and made free of all foreign materials including
dirt, grit, roots, grease, sludge and all debris or material that may be
attached to the wall or bottom of the manhole.
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A.
High pressure water blasting with a minimum of 3000psi to clean and
free all foreign
material within the manhole. |
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B.
When grease and oil are present, a diluted muriatic acid wash shall
be used integrally
with
the high pressure cleaning water. |
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C.
All loose or defective brick, ledges, steps and protruding ledges
with may interfere with
the
liner placement shall be removed to provide adequate spacing between the
wall and
liner
forms.
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4.2
Sealing
Active Leaks
All
active leaks shall be stopped using an approved rapid setting non-shrink,
expansive cement, or other approved products.
4.3
Invert
Repair
4.4
Concrete
Liner Mix
The concrete liner mix shall be Type I or II Portland cement with
pea-gravel or ½ inch minus coarse aggregate with fiber reinforcement,
producing an average compressive strength of 4500 psi when fully cured.
The liner mix shall be placed with a two to three inch slump. Other
additives may be added to assist in placement or necessary due to weather
conditions.
4.5
Interior
Liner Form Installation
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4.5.1
Measure the inside diameter of the manhole to be rehabilitated.
This will determine the appropriate adjustable liner knockouts (three sizes)
that are to be used. These knockout adjust the liner panels from 36” to
42” I.D. which after the liner mix is placed, will give a new 3”
concrete liner in a existing 42” to 48” diameter manhole. Note: One
liner ring consists of 3 liner panels and 3 adjustable knockouts. The
height of each liner panel is 15” in height.
( Small diameter liner panel sets are available which adjusts
from 32” to 38”) |
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4.5.2
The liner rings can be places flat on the existing bench of
manholes or can be set up on 2x4 legs for height adjustment. Spillage of
the concrete liner mix on bench when set up on 2x4 legs can be used to
rework bench if invert and benches have not yet been rehabilitated prior
to liner form placement. Once set up has been determined, the liner panels
are passed through the manhole casting and assembled inside using form
pins. Liner rings are stacked one upon another and secured to each other
using 11/2” C-clamps. Proceed upward, securing each liner ring, until
the bottom of the existing cone section is reached. The 24” liner cone
is assembled with the correct knockouts to match liner rings and secured
to the uppermost ring. |
4.6
Liner Mix Placement
After a pouring cone is positioned over the liner cone section, the
4500 psi pea-gravel liner mix is now ready to be placed. As the liner mix
builds up on the pouring cone, evenly distribute the mix, by hand, around
the liner rings from bottom to top of the structure.
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4.6.1
The liner mix shall be carefully vibrated, using an electric
vibrator with a 1” head, to ensure a new consolidated interior wall
free of honeycomb and voids. Carefully vibrate from bottom to top in
such a manner as to prevent segregation of the cement from the
aggregate.
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4.6.2
If 2x4 legs were used in the setup, enter the structure at this
time and float out the liner mix,
creating a
smooth transition from the bottom liner ring to the invert. Any liner
mix, which may have entered the
invert, shall be removed now. |
4.7
Curing
Curing
takes place once the manhole cover is replaced. It is important that the
cover is replaced within a few minutes after completion to avoid moisture
loss in the manhole due to sunlight and winds. The liner mix will
sufficiently cure within 2 to 4 hours, weather permitting. This minimum
time is needed, as not to cause damage to the new interior wall when the
liner rings are disassembled and removed from the structure.
4.8
Liner Form Removal and Inspection
If 2x4 legs were used in the setup, remove the legs as soon as the
liner mix has made its initial set. Starting from the liner cone and
proceeded downward, remove the form pins and lightly pry the knockouts
from the panel sections. Next, remove each panel section and pass each
carefully back through the casting.
4.8.1
Upon completion, the liner forms shall be wiped clean and
made ready for the next manhole. Also, at this time, the job site shall be
cleaned and excess material or debris be properly disposed of.
The
Interior Forming System by ICM is an economical method to control
infiltration and repair structurally defective manholes. The entire
process can be completed within 2 to 3 man hours without interruption of
sewer flows through the invert or at elevated points of entry. |
