CONCRETE PIPES INSTALLATION SOME IMPORTANT STEPS AS A GUIDE FOR INSTALLATION

It neither replace nor supersede project specifications or contract documents

 

TRENCH EXCAVATION :

The most important excavation limitations are trench width and depth. As excavation progresses, trench grades should be continuously checked against the elevations established in the pipeline profile. Improper trench depths can result in high or low spots in the line, which may adversely affect the hydraulic capacity of the sewer or culvert and require correction or additional maintenance after the line is completed.

The backfill load transmitted to the pipe is directly dependent on the trench width. To determine the backfill load, the designer assumes a certain trench width and then selects a pipe strength capable of withstanding this load. If the constructed trench width exceeds the width assumed in design, the pipe could be overloaded and possibly structurally distressed. Because the backfill loads and pipe strength requirements are a function of the trench width, maximum trench widths are usually established in the plans or standard drawings. Where maximum trench widths are not indicated in any of the construction contract documents, trench widths should be as narrow as possible, with side clearance adequate enough to insure proper piping installation and compaction of backfill material at the sides of the pipeline. The following trench widths can be used as a general guide for circular concrete pipe:

Trench Width for Concrete Pipes

NOTES:

1. The dimensions shown on the drawing must be strictly adhered to.

2. To avoid accidental slips the trench should preferably be lined with trench sheeting. The sheeting being withdrawn progressively as the work advances before backfilling is placed. any soft area on local hard spot in the bottom should be well dug out and the bottom level restored in well tamped granular material.

BEDDING

1. Selected free-draining compactable granular material such as gravel or crushed stone of approximately 10mm size well tamped under and alongside the pipe.

2. Uniform compactable material free from tree roots,vegetable matters, clay lumps, etc.well tamped by hand in 75-150mm layers.

3. Uniform compactable materials as (2) but lightly tamped by hands.

4. Normal backfill in accordance with General Specifications.

WORKMANSHIPS

All aspects of workmanships shall comply with the ‘‘GENERAL SPECIFICAIONS FOR ROADS AND BRIDGE CONSTRUCTION’’ issued by the Ministry of Communications, Kingdom of Saudi Arabia and its addendum and special specifications.

REMARKS:

1. INFORMATION SHOWN ARE FOR REFERENCE ONLY.

2. FOR EACH PROJECT THE RELEVANT DESIGN SHALL PREVAILE.

 


BEDDING

The bedding is the cushion material between the pipes and the foundation. Its function is to ensure uniform support for the pipeline both with regard to grade and hardness. A bedding specification must form part of any pipe laying specification as it influences the pipe strength required.

The best bedding material is granular and uniformly graded which assists in handling and spreading. It only needs sufficient compaction to ensure that laying tolerances are maintained when pipes are laid and backfilled. Holes (recesses) in bedding must be provided for the protruding socket to ensure uniform support of the barrel and hard point supports must be avoided.

 


LAYING THE PIPES

Before handling the pipes check their mass and make sure the handling equipment is of adequate strength. Pipe laying usually progresses in an upstream direction with spigots pointing downstream having been inserted into the socket. Doing it this way restrains the joints from opening up as a result of pipeline movement and joint surfaces are protected against entry of foreign matter.

To ensure pipes are laid to correct grade within specified tolerances some installers will opt to lay pipes on timber, brick or stone supports. Such supports if placed on a hard foundation can result in damage to the pipes on account of the point load (concentrated reaction) they impose on the pipe when backfilled. Such supports must be removed before backfilling. The desire to achieve tight laying tolerances for line and grade must not result in the uniform support of the pipe being compromised or sacrificed.

Rubber ring jointed pipes must be laid with joint gaps between the pipes to ensure that the lines are able to deflect without damage to the pipes. The rolling ring must be assembled dry and without the use of lubricant whereas the skid ring type requires lubricant. All flexible gasket materials not cemented to the pipe, including joint lubrication compounds, should be stored in a cool dry place to be distributed as needed. Rubber gaskets and preformed or bulk mastics should be kept clean, away from oil, grease, and excessive heat and out of the direct rays of the sun.

JOINTING

Before jointing clean and inspect all joint surfaces. Dirt dust and foreign matter must be removed from the spigot and socket, pipes with damaged joints must be repaired or discarded, rolling rubber rings must be clean and dry - damaged rings must not be used.

Place the rubber ring on the spigot and ensure the ring is free of kinks and twists and is uniformly tensioned. To ensure this happens lift the ring away from the circumference of the pipe at several places, each time letting it spring back. The spigot is then offered to the socket with uniform contact for 360 degrees to the socket lead in. The pipe is then pushed home. Up to DN600 pipes can usually be barred home and a block of wood should be placed near the invert (to prevent steel to concrete contact) and protect the socket.

 

 

CURVED ALIGNMENT

Changes in direction of sewer lines are usually accomplished at manhole structures, while grade and alignment changes in concrete pipe sewers can be incorporated into the line through the use of deflected straight pipe, radius pipe or specials. Since manufacturing and installation feasibility are dependent on the particular method used to negotiate a curve, it is important to establish the method prior to trench excavation. For deflected straight pipe the joint of each pipe section is opened up on one side while the other side remains in the home position. The difference between the home and opened joint space is generally designated as the pull. The maximum permissible pull must be limited to that opening which will provide satisfactory joint performance. This varies for different joint configurations and is shown at the pipe manufacturer’s catalogue / shop drawings.

BACKFILLING

The most important point about backfilling is to realize that the compaction loads/ construction vehicle loads will in most cases be the most severe load to which the pipe is subjected. Make sure the designer has allowed for this.

1. Avoid damaging the pipes by direct impact. Keep heavy rocks and other such material out of the fill adjacent to the pipe and the embedment zone.

2. Bring up the fill on both sides together to ensure pipeline alignment is maintained. Use a hand held compactor to do this.

3. Avoid running heavy construction equipment over the pipes in an uncontrolled manner.

4. Ensure the detail of the backfill is clearly understood and the grade of installation is nominated on the drawings. Do not use construction vehicles that were not allowed for in the design. Make sure the designer has nominated construction vehicles. If a non-specified vehicle is to be used check that it’s OK , with the designer prior to installation.

5. Ensure that the pipe is compacted with a pedestrian roller to the requisite level over the top of the pipe prior to bringing on compaction and construction loads.

6. If the backfill procedure is to be varied from design then seek approval from designer.