Buried

—————-

Installation of Buried FRP Pipes with Reka Coupling Jointing System

In general the followings provide two commonly used onshore installation methods and several for offshore installation.

Installation Type1

  • Open required trench and level its bottom according to project plan & profile drawings.
  • Provide the pipeline with at least 100 mm thickness of bedding using type B of soil as described in table 1 with minimum compaction of 85%.
  • Lay down the pipes and connect them according to the provided handling and installation procedure.
  • Backfill the pipe zone up to minimum of 300mm above pipe crown using aforesaid backfilling material.
  • For non-pressure (PN<1 bar) part of pipeline the requirement of compacting of soil over the pipe crown does not compulsory and also native soil may provide adequate strength to form soil-pipe mechanism. Using native soil to fill the pipe zone is only allowed following Farassan’s written approval.

Installation Type2

This method is used when trench wall is strong enough to support pipe in terms of not allowing any ovality. The steps are more or less similar to type 1 while there are few changes in backfilling the FRP pipeline.

  • Open required trench and level its bottom according to project plan & profile drawings.
  • Provide pipe with at least 100 mm thickness of bedding using type B of soil as described in table 2 with minimum compaction of 85%.
  • Backfill pipe zone up to level of 60% of pipe diameter using the specified backfill material and compact to the required relative compaction level.
  • Use approved native soil to backfill from 60% of diameter upward with a relative necessary compaction to achieve a minimum soil modulus of 1.4MPa.
Note: Installation type 2 is not applicable to small diameter pipes.
Note: Installation type 2 is not suitable for high traffic load conditions.
Alternate installations to accommodate a specific field condition include wider trenches, sheet piles, soil stabilization, use of geotextiles and etc. is to be consulted with engineering department of Farassan©.

As FRP pipe  of Faratec™ can be installed in a number of different situations including above ground, sub-aqueous, trench less and sloped applications, then more specifications, detail and planning may be required, therefore it is strongly recommended to contact engineering team of Farassan for consultation.

Trenching

The trench must be wide enough to permit placement and use of compaction equipment. Also depth of trench depends on pipeline profile drawn according to design requirements. In general speaking width of “2A+DN” shown on Fig 10 is approximately 1.5 times DN.
A typical trench detail for FRP pipe shall be as the followings,

The trench must be wide enough to permit placement and use of compaction equipment. Also depth of trench depends on pipeline profile drawn according to design requirements. In general speaking width of “2A+DN” shown on Fig 3 is approximately 1.5 times DN.
A typical trench detail for FRP pipe shall be as the followings,
Where rock, soft, loose, unstable or highly expansive soils are encountered in trench’s bottom, it may be necessary to increase the depth of bedding layer to achieve adequate longitudinal support. Minimum depth of trench shall be according to several parameters such as pipe diameter, level of underground water table, traffic load, pipe stiffness, working pressure of pipeline and etc. Please consult engineering team in this regard.

Bedding

As FRP pipes are flexible so bedding should be properly done not to loose this flexibility and also not to extend it to failure of pipeline system. Choosing right material for bedding with right compaction shall be according to geotechnical study of field. In a very common practice, bedding forms of minimum 100 mm thickness of the same material considered for initial backfilling with at least 85% of compaction. It is suggested to provide Farassan’s engineering team with final and approved revision of geotechnical report so best technical and economical solution for satisfactory backfill underground pipelines. Following table gives general information about initial backfill materials.

Trench bottom should be over excavated at each joint location to ensure that the pipe has a continuous support and does not rest on the coupling.
Suitable materials for use as bedding material or for the pipe zone to 300 mm above the pipe are preferably materials of categories SC1 and SC2. The degree of compaction should reflect the static requirements. Do not drop stones larger than 200 mm on the 300 mm layer from a height greater than 2 meters. The backfill above the pipe zone may be made with excavated material with a maximum particle size of 300 mm. When the water table is above the trench bottom, the water level must be lowered to at least to the trench bottom prior to the preparation of the bedding. If the ground water cannot be maintained below the bed, filter cloth should be used to surround the bed and the pipe zone to prevent migration. In this case gravel or crushed stone should be used as bedding and backfill material.

Fig 5 - Proper Hunch Backfill
Table 2 - Initial Backfill Material – Refer to AWWA M45 for more detail
Table 2 - Initial Backfill Material – Refer to AWWA M45 for more detail
Fig 4 - General Correct Bedding
Fig 4 - General Correct Bedding
Table 1- Initial Backfill Material
Table 1- Initial Backfill Material
Table 3 - Compacting above FRP pipe
Table 3 - Compacting above FRP pipe

High Water Level / Flood Plainsand Buoyant Forces

Installing FRP pipeline in an area with high level of underground water or in flood plains, buoyant forcesand floatation shall be considered and pipeline shall be well supported not to loose stability as a result of those forces. To keep pipeline in a safe range, following table provides minimum coverage height of soil according to pipe diameters.

To prevent flotation in situations like concrete encasement in order to restraint pipes against movement usually done by strapping over the pipe to a base slab or other anchors. Minimum strap properties is width of 25 mm and strong enough to bear the buoyant forces. Following table gives maximum strap spacing according to pipe diameters.

In case concrete encasement maximum clearance between pipe’s bottoms to top of bedding is given in the following table according to pipe stiffness. Note that, it is recommended to consult Farassan’s engineering team for proper details.

Table 6 - Maximum Lift * Recommended to consult Farassan’s engineering department for all specific situations
Table 6 - Maximum Lift * Recommended to consult Farassan’s engineering department for all specific situations
Table 4- Minimum soil height on empty pipe * Recommended to consult Farassan’s engineering department for all specific situations
Table 4- Minimum soil height on empty pipe * Recommended to consult Farassan’s engineering department for all specific situations
Fig - 6 Pipe Anchoring
Fig - 6 Pipe Anchoring

Thrust Forces

In pressurized (working pressure above 1 bar) pipelines inevitable unbalanced forces develop at each and ever direction change, which is so called Thrust Forces. In order to preserve pipeline’s stability and reduce the risk of jointing system displacement, thrust blocks shall restrain these thrust forces. Nozzle connections with less than 300 mm of diameter and headers with diameter of bigger than 3 times of nozzle diameter are exceptional and no need for thrust blocks on them. Traditionally, thrust blocks are designed as rigid reinforced concrete structures in which angular deflection and misalignment at joints close to them shall be avoided during installation. Note that Bi-Axial pipes as explained before are designed to withstand thrust forces by its body structure so in case of using this class of Fiberglass reinforced polymer (GRP) of Faratec™ the pipeline has no longer requires thrust blocks at any point. In general connecting FRP pipes to rigid structures such as thrust blocks causes stress increase at points where FRP pipe enters and leaves the structure, therefore not only aforementioned angular deflection and misalignment must be avoided, also actions must be taken to stop or reduce development of such stresses. There are two options for those purposes as described in Fig 7 and 8 below.

Fig 7-Option 1 for connecting FRP pipe to rigid structure Use of coupling and sort piece
Fig 7-Option 1 for connecting FRP pipe to rigid structure Use of coupling and sort piece
Fig 8 - Option 2 for connecting FRP pipe to rigid structure Use of Rubber and sort piece
Fig 8 - Option 2 for connecting FRP pipe to rigid structure Use of Rubber and sort piece
Diametrical Deflection

Faratec™ Uni-Axial pipe that works perfectly with flexible jointing system of Reka Coupling is suggested for this project. Initial allowable vertical pipe deflection for installed pipe is 3% and 5% of pipe diameter for pipe diameter of less than or equal 300 mm and greater than 300 mm respectively. Pipes with initial deflection exceeding the values above shall be installed.

Where Actual ID is calculated from the following equation measuring diameters of pipe not yet installed laying loose on a proper surface.

Horizontal & Vertical ID
Horizontal & Vertical ID
Installation of GRP pipe