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Laying and Jointing of Precast Concrete Pipes

What is the process of Laying and Jointing Precast Concrete Pipes?

Here is an Engineer direction about supply and laying of precast concrete pipes , including pipe-jointing material, in those structures where the installation of R.C. pipes is as required in the site situation.

The pipes are reinforced concrete non-pressure pipe to be furnished in accordance with the reinforced concrete pipes Class NP2 and Class NP3 of IS 458.  The pipe diameter to be used in each location is shown on the Drawings or is as specified by the Engineer.  The class of reinforced concrete pipes is as indicated in the Drawings.

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Materials forPrecast Concrete Pipes

The material used in the manufacture of reinforced concrete pipes is conformed to the following requirements:

A.   Cement: In accordance OPC  cement.

B.   Water: In accordance with water section.

C.  Additives: All concrete used for the manufacture of pipes contain entrainment of not more than 2.5 percent of air, by volume, in the concrete as discharged from the mixer.  Calcium chloride is not used except when approved by the Engineer.

D.  Aggregates: Fine and coarse aggregates for concrete shall be in accordance with Section17, except that other grading may be used.  The maximum size of coarse aggregate for each size of pipe shall be the largest size compatible with a satisfactory placing of the concrete.

E.         Reinforcement Steel: In accordance with the specification.

Precast Concrete Pipes Installation

During manufacturing, transporting, storing, and laying of concrete pipes, the pipes shall not be dropped or handled in a way that might crack the wall or otherwise cause damage. 

The pipes shall not be moved until after the specified curing period.  Any length of pipe that, in the opinion of the Employer’s Representative, is damaged beyond repair, shall be removed from the site of the work and replaced by the Contractor at his own expense.

Trench Excavation

The trench for laying precast concrete pipes shall be carefully excavated to required lines and levels shown on the drawings or to such other lines and levels as the Employer’s Representative may direct.

The sides of excavations shall be supported where necessary to ensure their stability; if for any reason, portions or a trench whether supported or unsupported should give way, the Contractor shall excavate and remove at no extra cost of the Employer, such disturbed ground until the trench is to the satisfaction of the Employer’s Representative.

The thickness and shape of foundations shall be as indicated on the drawings or as directed by the Employer’s Representative, according to soil conditions. 

If soft material is encountered such materials shall be excavated and removed, or if the trench bottom is unstable the invert of the trench shall be excavated below the level specified and brought up to the required level by suitable fill materials thoroughly consolidated to at least the same degree of compaction as the undisturbed material as directed by the Employer’s Representative.

Bedding of Precast Concrete Pipese

Excavation of pipe trench shall be done to the grade and line shown on the Drawings.  The pipe shall be supported firmly throughout its entire length.

Bedding of reinforced concrete pipes shall conform to the requirement given below for compacted earth cradle or concrete cradle, whichever is called for on the Drawings or otherwise directed by the Employer’s Representative.

If the type of bedding is not shown, compacted earth cradle shall be provided.

A.   Compacted earth cradle: shall be constructed by bending the pipe in a shallow trench cut in compacted earth layers to a depth of not less than 10 cm and shall be accurately shaped by a template to fit the lower pipe exterior for the specified embedment.

B.         Concrete cradle: a concrete cradle for pipe shall consist of a continuous concrete cradle constructed of Class C concrete in conformity with the details shown on the Drawings and requirements of Section.

Laying ofPrecast Concrete Pipes

The method of lowering the pipes into the trench and laying them in position shall be such as to prevent dirt from entering the pipe and couplings and to prevent damage to the pipe.  Before and during execution of the joints all surfaces shall be clean and free of mud, oil or grease.  The pipe shall be aligned straight with ends squared, and the joining of pipe sections shall be such as to produce watertight joints.

Joints and Collars and Pipe Bend Joint

A.    Joints

Pipe joints shall conform to the type as shown on the Pipe Installation Drawing.

If the joint of pipe is not indicated on the section and plan of the structures required, flush joint shall be provided. Cement mortar used in jointing shall be 1 part of cement and 2 parts of sand, conforming to the requirements of Section

B.    Collar and Pipe Bend Joint

The collars and pipe bend joints shall be constructed where shown on the Drawings, and the concrete shall conform to concrete Class A in Section 17 and reinforcement steel shall conform to Section.

Water Testing

Where required by the Engineer, sections of pipeline shall be tested for leakage, before backfilling.

Backfill

As each unit of the pipe is laid, sufficient backfill material shall be tamped about the pipe to hold it rigidly in place until the joints are completed.  After the joints have been completed, the backfilling shall be completed as hereinafter specified. 

Loads up to the design loading will not be permitted to travel over the pipes until backfill and embankment material has been placed to a minimum thickness of at least 0.50 m over the top of the pipe. 

This minimum cover requirement is not always adequate during construction when equipment heavier than design traffic loads are routed over or close to the installed culverts.  The Contractor shall be responsible for providing the additional cover necessary to avoid damage to the pipes due to such loads.

Measurement  ofPrecast Concrete Pipes

Measurement for direct payment of furnishing and laying the precast pipes will be made along the centreline from end to end of the pipe in place and no allowance will be made for the lap of joints.

The Contract Unit Prices covering the supply and laying of pipes shall include the entire cost of furnishing the pipes and all materials for joints and lean concrete bedding if needed, the cost of all labor and equipment required for transporting, laying, jointing and bedding the pipes.

The supplying and laying of pipes of each diameter will be paid per linear meter of pipe actually laid, while the excavation and backfilling shall be paid per cubic meter, at the appropriate Contract Unit Prices.

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