The basic requirements are to trench, place straight joints of pipe to span the road whilst maintaining the flow of traffic by plotting the trench or providing a temporary diversion road. Work on this type of crossing will be done ahead of the mainline section(s) to allow tie-in welding to be done immediately the relevant tie-in crew reaches each crossing. Crossing will be done by open-cut and thrust boring.
Open cut Methode
- For open-cut crossings, the crossing pipe shall be laid in the prepared ditch assuring specified minimum cover. Pipe shall be bedded in clean sand, free of rocks and organic matter, extending 180 mm radially from the outside surface of the pipe.
- For open-cut track crossing, the remainder of the ditch backfill shall consist of material similar to the existing track backfill. It shall be placed in maximum lifts of 180 mm and compacted sufficiently to minimize any settlement of the travel surface through the ditch cut.
- Proper warning signal shall be installed and maintained in accordance with the regulations issued by the concerned authorities.
- Temporary by-pass shall be constructed in order to ensure the continuity and safety of traffic
- Trenched installation would be done with excavator or any other suitable method.
- Crossing shall be designed as ancased using pipe of the same design factor as the adjacent class location and through the concrete box culvert on pile found. The minimum depth of cover shall be 2.0 meters below the road and its adjacent ditches.
Thrust Boring Methode
Prior to the construction of a pipeline crossing, arrangement should be made with the authorized agent of the facilities to be crossed.
Supply equipment, tools, material and labour in order to perform crossing work
Prepare, propose and affirm crossing method for each crossing regarding the nature of crossing.
Accomplish crossing work base on related drawing and specification. The work at crossing include, but not limited to :
Supply equipment, tools, material and labour in order to perform crossing work
Prepare, propose and affirm crossing method for each crossing regarding the nature of crossing.
Accomplish crossing work base on related drawing and specification. The work at crossing include, but not limited to :
- Necessary clearing
- Grading and trenching to the required depth and widths.
- Installation and testing of pipe.
- Temporary facilities.
- Restoration of the disturbed structure or obstacle to the original conditions.
- Installation of protective works such as concrete weighting, etc
- Perform crossing for fibre optic cable where applicable as per standard detail.
Supply equipment, tools, material and labour in order to support ThrustBoring work:
- Transport pipe material to crossing point.
- Fabricate steel pipe string and hydrostatic test.
- Fabricate pulling head.
- Position steel pipe string on pipe rollers.
Crossing of hard surfaced (asphalt, bitumen, concrete) or public roads shall be designed to permit installation by boring without disturbance to the road surface.
In approaches to crossing, bending of pipe shall be minimized as much as possible by gradually deepening the trench.
The depth of cover shall conform to the requirements at the authority having jurisdiction but shall not be less than 1.2 m at any point in the road reserve.
Crossings of paved roads and railroads shall be installed by thrust boring. Casing shall be used for safety pipeline 6”.
The angle of intersection between a pipeline crossing and the road crossed shall be as near to 90 degrees as practicable. In no case should it be less than 30 degrees.
8.2 Trenching
Trenching Pre-construction checks.
Prior to trenching the Foreman completes the Trenching Preconstruction checklist whilst completing the following check:
- The foreman checks that the alignment is clearly surveyed and installs any trench markings by measuring from the trench centreline offset pegs previously installed by surveyor.
- Temporary access around the trench for local transportation and other requirements including traffic safety signs are provided,.
- The foreman checks document for underground services and locates them by hand digging.
Trenching Operation
The Foreman ensures that the following requirements are satisfied:
- The trench is the required width and depth, and is configured in accordance with the minimum allowable roping radius of the pipe.
- Locations requiring extra width or depth are properly and safety trenched in accordance with accepted practice.
- The material excavated shall be stored clear of the crossing.
Tie-In Welds
- Tie-in welds will occur at both sides of the road crossing and will be done by the mainline tie-in crew(s).
- The alignment and gap set-up of the ends is considerably more difficult to achieve than for production welds, because the overlapped pipes require accurate cutting to form a one weld tie-in or an additional pipe length has to be cut where there is a gap between strings to form a two weld tie-in.
- Localized enlargement of the trench (bell hole) will be provided to allow adequate welder access. Shoring will be installed where necessary to ensure safe working conditions in the bell hole.
- An external applied line-up clamp is used to hold the ends for welding after cutting the sizes. Actual welding procedure is essentially the same as for production welds except that the external clamp is released when 50% or more of the root bead has been deposited and there is no pipe movement until the weld is complete.
Lowering-in
Preconstruction Checks
Prior to the lowering-in operation the Foreman completes the Lowering-in Preconstruction
Checklist whilst performing the following checks:
- Ensures he has up to date copies of Alignment Sheets, and all necessary permits covering R.O.W. access.
- Inspection of trench for the section being lowered to ensure that any loose rocks, sticks or other debris that may have fallen into the trench are removed and where required bedding material has been placed correctly to protect the pipe corrosion protection coating.
- Dewatering of the trench has been adequately carried out where necessary.
- That the holiday detector is calibrated and set at the correct voltage.
- That all field joint coating and repairs have been carried out in accordance with the relevant procedures.
Lowering-in Operation
On completion of the preconstruction checks the lowering-in operation commences as follows:
- The pipe is picked up at the starting point using side booms or cranes fitted with appropriate lifting belts.
- The holiday detector is attached to the pipe in a manner that provides full coverage of the pipe circumference and enables the detector to move along the pipe at the prescribed speed and the pipe string is electrically earthed.
- Immediately prior to lowering-in the pipe is holiday tested in accordance with the specified voltage and any defects detected are repaired in accordance with the relevant procedures and retested.
- The pipe is then lowered gently into the trench. Careful attention is paid to ensure the pipe is in the centre of the trench and rests on the bottom of the trench.
- External force shall not be applied to force the pipe to the bottom of the trench. Should the pipe not rest completely on the bottom of the trench, then the pipe shall be supported with sand bags before backfill
Backfill
Backfill Preconstruction Checks
The Construction Superintendent is responsible for ensuring that backfill is installed correctly.
Notwithstanding this, the Foreman does not use any material he considers unsuitable.
Prior to commencing backfill in an area the Foreman performs the following checks and completes the Backfill Preconstruction Checklist:
- Ensures that he has the necessary Permits on the R.O.W. at all times.
- Ensures that backfill material is free of any material that could damage the coating of the pipe and in accordance with the relevant Authorities requirements for road base materials.
- Ensures suitable padding material is available where required.
- Checks the location of any cathodic protection (C.P.) test point leads to make sure backfilling can take place without damaging the leads.
- Checks for sand bags supporting the pipe and ensures they are 'knifed' immediately before backfilling commences.
- Checks that the As-Built Traceability Survey has been completed for the next section to be backfilled.
Backfill Operations
Backfill operations will generally be performed using suitable material in the steps listed below.
Note that due to the variations in local conditions along the pipe alignment, the Foreman will use his discretion in applying the methods described here.
- Places padding material to surround and cover the pipe to a depth of 150 mm above the top of the pipe where required.
- Carefully place material into trench with excavator or front end loader progressively backfilling until sufficient cover over the pipe has been achieved to provide a working zone for the first stage compaction.
- Selected road backfill material will be placed in increments of approximately 150 mm and compacted with a plate or vibrating roller compactor in accordance the local Authority requirements.
- Place concrete slabs (during the backfill process) in accordance with the drawings where required.
- Marker tape is installed during the backfill process at road crossings where required.
- Caution is exercised around cathodic protection cables to ensure that no damage is caused.
Use of Backfill Checklist
The Foreman prepares one Backfill Checklist for each day's operation. At the start of the day the Foreman fills out the planned work for that day. The Foreman then carries out the preconstruction checks, completes and signs the form.
The remaining items are signed off at the completion of the day's work. The checklist is then forwarded to the Construction Superintendent.
Inspection And Test Report
Inspection would be performed by QC Inspector to ensure that the whole activities of road crossing is in accordance with project specification. The inspection shall be cover but not limited to:
- Check bottom of ditch, deep of pipeline to the surface of road and length of crossing pipe against reference drawing.
- Check distance of pipeline to other structure, cable or any foreign pipe minimum clearance is 500 mm).
- If additional backfill material beyond that available from trench excavation is required, borrow soil shall be furnished (check borrow soil from debris, foreign material).
- Ensure backfilling is compacted up to 90% of maximum dry density for road crossing.
- The Construction Superintendent completes a Daily Progress Report for each day's operation at the end of the day's work.
