Manhole Installation

Installation Instructions

Fiberglass manholes must be installed according to these instructions. Local codes may apply and should be consulted as applicable in manhole installation. Fiberglass manholes require a proper concrete foundation, good backfill and proper handling to prevent manhole damage and insure long term corrosion resistant service.

1- Installation  instructions: for use with pipe up to 900 mm outside diameter with 1,200 mm manhole, or 700 mm outside diameter with 1,000 mm manhole.

1.1. Selecting Height

Height of manhole required is 300 mm less than distance from bottom of pipe to finish grade. This will allow sufficient clearance for at least one course of brick (or one concrete ring) to adjust ring and cover to finish grade.

1.2. Handling

Do not drop or impact manhole. If manhole must be rolled, insure that ground is smooth and free of rocks, debris, etc. Lift manhole with two slings on spreader bar in horizontal position or by use of 10 cm x 10 cm timber. inserted through top access hole, as shown, for vertical positioning. The timber shall be 250 mm longer than the manway diameter.

1.3. Site Preparation

Excavation at manhole location should be at least wide enough to accommodate the slab specified and to provide working room around manhole. Slab should be at least 1.8 m x 1.8 m square or 1.8 m in diameter. All pipes connected to the manhole should have a flexible joint within one pipe diameter beyond the connection.

1.4. Flowline Cut outs

Pipe cut outs at the flowline are made in manhole barrel prior to setting manhole in place over pipe in trench. Quarter marks have been provided on barrel to facilitate alignment of cut outs. The size of the flow line cut out is determined as follows: 

• Max. single cut out size is 950 mm diameter for 1,200 mm manhole and 750 mm for 1,000 mm manhole.
• Sum of all cut out diameters not to exceed 1,900 mm for 1,200 mm manhole, and 1,500 mm for 1,000 mm manhole.
• Minimum circumferential distance between any two cut­outs is 300 mm.
• Height of cut out shall be sufficient to insure that top of manhole when set in place will be below finish grade, to allow for final adjustment of chimney and ring and cover.
• Height of cut out should be deep enough to insure that a minimum of 100 mm of manhole base will penetrate con­crete slab.
• Use gasoline or electric power saw with a masonry blade (carborundum or equal) for making cuts to manhole. Make cut out to conform as closely as possible to pipe O.D. plus 15 mm. Ncie: Cutouts for drop manholes to accommodate laterals should be made in accordance with Section 3.1. Flowline cut outs.

1.5. Installation Procedure

• With cut outs made, position manhole so that it may be set in place with backhoe or other lifting device.
• Pour ready mix concrete in excavation to form slab at least 150 mm thick x 1.8 m square.
• Lower manhole in place until top of cut out gently rests upon pipe.
• Plumb manhole and work concrete around manhole and over the pipe, forming a tight seal at least 150 mm high.
• There must be a minimum 50 mm thick concrete bearing surface beneath bottom edge of manhole.

2. Installation instructions: for use with pipe larger than 900 mm/700 mm outside diameter.

Note: Handling and site preparation procedures are similar to Section 1. Please read previous instructions thoroughly.

2.1. Selecting Height

Height of manhole required is 300 mm less than distance from top of pipe to finish grade. This will allow sufficient clearance for at least one course of brick (or one concrete ring) to adjust ring and cover to finish grade.

2.2. Rigid Pipe (concrete, clay, etc.)

 

• Embedment

Embedment and backfill material beneath and around pipe and manhole shall be pea gravel, crushed stone or crushed gravel per ASTM C33 gradation 67 (grain size 3/a in. to 3/6 in.). A minimum of 150 mm of embedment material must be placed in bottom of trench, under pipe. Width of embedment and backfill should be 300 mm to 450 mm wider than pipe. Backfill trench around pipe to within 150 mm of top of pipe. Use of wood forms cut to shape of pipe will help contain backfill material in position under manhole.

• Installation Procedure

Suspend manhole over pipe and stabilize in plumb position. Pour concrete slab over embedment material and around manhole and pipe to a depth of at least 150 mm above manhole barrel. Total thickness of slab must be at least 300 mm. Slab should be 1.8 m in diameter or 1.8 m square minimum. Work concrete around manhole to form tight seal.

• Backfilling and Finishing

Do not backfill until concrete base has hardened suffi­ciently to provide adequate support for manhole and back­fill material. Backfilling procedure and material depend on native soil conditions and manhole height; refer to following instructions for backfilling and finishing procedure.

2.3. Flexible Pipe (Steel, fiberglass, PVC, etil)

• Concrete Base

Pour concrete slab base at least 150 mm thick. Slab should be at least 1.8 meters long and at least 300 mm wider than pipe O.D. Lay pipe into wet slab, insuring mini­mum of 150 mm thickness under pipe. Pipe should have flexible joint (such as coupling) within one pipe diameter on both sides of manhole.

• Installation Procedure

Suspend manhole over pipe and stabilize in plumb posi­tion. Do not allow manhole to rest directly on pipe. Build forms necessary to contain concrete poured around pipe and barrel of manhole. Pour concrete to a depth of at least 150 mm above manhole barrel. Resulting concrete block should be of same length and width as bottom slab and have a height of at least 300 mm greater than O.D. of pipe.

• Backfilling and Finishing

Do not backfill until concrete has hardened sufficiently to provide adequate support for manhole and backfill material. Backfilling procedure and material depend on native soil conditions and manhole height; refer to following instructions for backfilling and finishing procedure.

3. Details for backfilling and finishing-all pipe sizes.

 

Inverts and Laterals

The invert should be formed in accordance with standard procedures. There is no difference between Amiantit and other manholes in this procedure in the event that one or more laterals are to be fled into manhole, standard drops should tie used. No cut out large than 300 mm in size should be used for a drop. No cut ow for a drop of any size should be placed in manhole greater than 4 meters from the surface without consulting Amiantit Fiberglass. Use gasoline or electric power saw with a masonry blade (carborundum or equal) for making cuts. Make cut outs to All conform as closely as possible to pipe O.D.

Finishing Manhole to Grade

Construct chimney on flat shoulder of manhole using brick and mortar or precast con­crete rings. Use chimney for ring support. Do not in any case place cast iron ring directly on Amiantit Manhole. Do not load manhole except on flat shoulder.

Backfilling

In each of the following cases, care should be taken to avoid uneven backfill loads on manholes. Prevent equipment and backfill material from impacting manhole. Be careful that sides of excavation do not slough off, causing load concentration on side of manhole. Do not permit ground­water or surface runoff to accumulate in open excavation around manhole which has not been completely backfilled.

 A) Stable Soils Bearing capacity greater than 9.8 tons per sq. meter. Backfill around manhole with native soil to the flat brick ledge at top of reducer section; insure that large soil lumps, rocks, concrete, etc. over 50 mm in size are not present in backfill. Backfill should be placed evenly around manhole in 300 mm maximum lifts. 

B) Unstable Soils and High Water Tables Bearing capacity less than 9.8 tons per sq. meter. In unstable soils, such as expansive clay, quick sand or marsh, and/or where water table may be less than 1.5 m from finish grade, backfill must be stable soil or sand, and must be com­pacted. A minimum 600 mm surround of sand or select backfill must be placed in 300 mm maximum lifts adjacent to the manhole and compacted to 85% Standard Proctor Density up to flat brick ledge. 

C) Manholes greater than 6 meters in height All such manholes have to be installed as in 3B above for Unstable Soils and High Water Tables.

4. Manhole Re Excavation Procedure:

• Manholes may be re excavated for installation of laterals. However, care must be taken to avoid damage to manhole.
• Start excavation approximately 3 meters from manhole center line. Dig toward both sides of manhole at 600 mm depth. Stop digging when bucket is about 600 mm from manhole (leave 600 mm of soil around manhole; soil will slough into excavation when hole is 1.5 meters deep.)
• After both sides of manhole have been excavated 600 mm deep, reposition backhoe 90° to first setup. Repeat step (A), digging to 1.2 meters depth.
•  Continue working around manhole until excavation is sufficiently deep, all the while observing these rules.

1. Dig from outside of hole toward manhole.
2. Do not get bucket closer than 600 mm from manhole.
3. Do not push soil toward manhole with bucket.
4. Do not dig directly toward manhole only at sides. Rotate backhoe position 90° to excavate other sides
5. Do not permit groundwater or surface runoff to accumulate in open excavation around manhole which is not completely soil supported. 

5. Modifications

Field repairs to Amiantit manholes should not be attempted prior to consultation with an Amiantit Fiberglass or designated representative. Installation of Steps Amiantit Fiberglass manholes are supplied without steps or ladders. However, if a particular application calls for steps, they can be installed on the lob site by either bolting through the manhole wall (sealing with silicone caulking) or bonding a ladder to the wall with Fiberglass lay-ups. 

6. Environments

(except sanitary sewers) All manholes except those installed in sanitary sewers must be installed in environments approved in advance by a duly authorized representative of Amiantit Fiberglass Industries Ltd. Any loss resulting from installation in an environment not approved by Amiantit Fiberglass shall not be the responsibility of Amiantit Fiberglass Industries Ltd.