This method utilizes preformed Polypropylene (PP) liner segments, welded into sections and inserted into existing concrete or brick sanitary sewer structures, either for rehabilitation or retrofit applications.
Option 1 requires excavation and removal of existing manhole cast iron frame with lid, chimney and corbel-cone (or flat slab top); insertion of the prefabricated Polypropylene (PP) liner sections and installation of a new precast F.R.P. or HDPE / PP lined corbel-cone (or flat slab top).
Option 2 does not require the removal of the frame with lid. The Polypropylene (PP) liner segments can then be lowered into the existing structure where they shall be welded together into sections in situ.
POLYPROPYLENE (PP) LINER MATERIAL:
The prefabricated Polypropylene (PP) liner sections shall be composed of 100% polypropylene with a minimum thickness of ¼"(6 mm). The sections shall be non load bearing components which are resistant to the chemical environment normally found in the waste water collection system to which they will be exposed. The outer surface of the liner shall have ribs molded in opposing directions on the vertical axis and waterstop turnbacks on the horizontal axis to lock the liner into the grout upon hardening .
The prefabricated Polypropylene (PP) liner sections diameter shall fit into the existing structure such that a minimum of 2.5 " (63 mm) annular space is available for “grouting” the liner to the existing concrete structure. The assembled prefabricated Polypropylene (PP) liner sections shall conform to the height of the corresponding manhole structure. Pipe connections shall accurately accommodate all existing inlets, outlets, drops and cleanouts and are to be “plumbed” through monolithically attached “Factory” installed pipe stubs. Watertight flexible rubber repair couplers and / or rubber boot seals are to be used as noted in the drawings or as directed by the engineer.
The contractor shall measure the existing manhole prior to installation to determine critical dimensions including (but not limited to) structure diameter, height, pipe connection elevation, type, size and pipe angle location. The contractor shall be responsible for liner installation and fit.
The contractor shall be responsible for the field welding of all PP manhole liner joints.
GENERAL: Excavate an area around top of existing manhole of sufficient width and depth to facilitate the removal of manhole frame, chimney, corbel-cone (or flat slab top).
PREPARATION OF EXISTING STRUCTURE : Clean all interior manhole surfaces by means of pressure washing/sandblasting to remove all scale, loose material, laitance, grease, sludge, organic material etc. Remove all loose or unsound concrete and mortar. Remove all protuberances – steps, hardware, brick (lift stations – pumps, plumbing and controls) that will interfere with liner installation. If necessary, use approved cleaners to remove grease, oil, and other matter that may prevent an acceptable bond between existing manhole wall and polypropylene liner. The interior surface should be tested for pH to insure all acid contamination has been removed. All other structural repairs deemed necessary shall be performed. Active leaks (infiltration) shall be stopped with hydraulic cement/mortar, injectable grout (or other approved materials).
NOTE: It may be necessary to plug sewer lines or cover invert to prevent extraneous materials from entering sewer lines. “By-pass” diversion pumping may be required to maintain sewage flow.
MORTAR BENCHING / CHANNEL INVERT AND LIFT STATION FILLET
All required remedial work is to be performed per the governing utility specifications to insure watertight pipe connections and proper sewage flow. The benching or fillet shall be leveled or modified to insure proper bedding and vertical alignment of the Polypropylene (PP) liner sections within the vertical shaft of the existing manhole or lift station. The mortar benching shall be raised to a level just above the crown of main channel inlet to accommodate the proper installation of the Polypropylene (PP) l iner sections.
MORTAR BENCHING SEAL A “bedding ring” of quick setting grout mixture shall be placed on the benching to achieve a good bottom seal in order to prevent loss of grout from annular space between riser sleeve liner and interior manhole wall. Polypropylene (PP) liner sections shall be lowered into “bedding ring” on prepared mortar benching. Allow sufficient cure of grout “bedding ring” before proceeding.
* IMPORTANT NOTE : Care must be given to insure proper vertical alignment of Polypropylene (PP) liner sections to maintain proper annular space orientation for full height of new liner assembly with existing structure. If existing structure is “out-of-plumb” a miter cut adjustment must be made at the bottom end of the first riser liner section.
A six to twelve inch height pour of high strength, non-shrink flowable/pumpable cementatious grout shall be placed above the initial bottom seal in the annular space between the liner and interior structure wall to facilitate bonding of the PP liner section(s) to the existing concrete structure.
** IMPORTANT NOTE: Polypropylene (PP) liner section interior must be fully supported during grout placement with expandable support ring fixture, inflatable rubber bladder or bracing / shoring forms to maintain proper riser liner geometry. Allow sufficient cure of grout before disturbing support fixture to avoid bulging or deflection of Polypropylene (PP) liner sections.
If existing structure has had extensive corrosion and structural deterioration / reduction of wall thickness, the governing utility may require inserting wire mesh or rebar reinforcement in annular space.
Deep manholes / lift stations may require multiple Polypropylene (PP) l iner sections which shall be assembled, sealed / welded, supported and grouted in stages as described previously in this specification. The Polypropylene (PP) liner sections shall be constructed to the prescribed height with the top of the “final” riser section having a level mortar “butt type” joint to allow for installation of either a new lined precast corbel-cone (PP or F.R.P.) or F.R.P. lined precast flat slab top.
The new lined precast corbel-cone / flat slab top shall have an I.D. corresponding to the I.D. of the Polypropylene (PP) liner sections. The internal flange joint between “final” Polypropylene (PP) liner and lined precast corbel-cone (or lined precast top slab) shall be sealed by hot air extrusion field welding.
An HDPE convertible collar shall be installed on top of the lined corbel-cone /flat slab top with masonry grade adjustment (brick courses, field poured concrete or precast grade rings) for setting cast iron frame. The Convertible Collar shall be inserted through compression seal gasket mounted in the lined corbel-cone / flat slab top with appropriate GU Convertible Collar gasket flange design.
The lined corbel / flat slab top having appropriate access way ID design and cast iron frame shall be sealed with approved preformed butyl strips. The manhole / lift station frame and lid shall be set to accurately conform to the finished ground or pavement grade as shown on the drawings or as directed by the engineer. Non-shrink mortar shall be used for installation of corbel-cone (flat slab top), masonry grade adjustment and cast iron frame in customary manner for proper structural assembly and to prevent ground water infiltration.
Interior surfaces of liner shall be completely free from pinholes, cracks, pits or defects, which are detrimental to the intended use of the liner. No Polypropylene (PP) liner sections shall have holes or openings, which will permit the passage of liquid or gases through the liner wall to the mortar/ concrete. There shall be no exposed mortar / concrete through inside liner surface to include (but not limited to) riser section joints, adjustment liner section joints, pipe penetrations and cast iron frame. All mechanical anchor attachments through liner surfaces must be sealed with an elastomeric sealant approved by the Polypropylene (PP) liner manufacturer.
There is no correlation between vacuum (air) and hydrostatic tests (see ASTM C1244-93).
Vacuum testing coupled with hydrostatic pressure (elevated ground water conditions) provides unreliable test results. Due to this inaccuracy Predl GU or GU companies shall bear no responsibility in the event of concrete manhole joint failure or failure due to poor integrity of the precast concrete.