CABLE TRENCH EXCAVATION FOR POWER CABLE: UNDERGROUND PROJECT
The exact location of each trench should be selected and approved by the Engineer before cable trench excavation for power cable of any underground cable project.
Trenches should be kept as straight as possible and each trench shall be excavated to an approved formation and dimensions and shall have vertical sides which would be timbered where necessary so as to avoid subsidence and damage.
It’s important to excavate up to depth of at least 100 mm below the base of cable laying. The bottom of each trench should be firm and of smooth contour. Where trenches pass from a foot way to a roadway or at other positions where a change of level is necessary, the bottom of the trench shall rise or fall gradually. Minimum width shall be at least 600 mm for a single cable. For multiple cables, the trench width would be determined from the minimum separation specified and diameter of cables and approved by the qualified Engineer.
The servicer should take reasonable precautions to prevent damage to the highway or ground surface from a slip or breaking away of the sides of the trench. The rate of rise or fall should be take in consideration.
It should be deal with and dispose of water so as to prevent any risk of the cables and other materials to be laid in the trenches being affected detrimentally. Necessary to provide facility of all pumps and appliances required and should carry out the necessary pumping and bailing.
It’s need to consider the provision be made during excavation for reasonable access of persons and vehicles to property or places adjacent to the route. This provision shall be maintained until restoration has been completed.
Before each excavation is commenced the contractor shall make written or documented application to the Engineer prior to starting work attaching with application a dimensioned sketch detailing and positioning the proposed excavation. No work may be commenced until the appropriate authority has issued a “Permit to Excavate” in accordance with the Letter of Application.
When the excavation for trenches have been accurately executed, notice shall be given by the contractor to the authority Engineer, Laying of cables or building of structures would not be started until the contractor has obtained the authority Engineer’s sanction to proceed with the work.
After any cable has been laid and until the whole of the cables to be laid in the trench have been covered with their protective covers shall be used in the trench or placed in such a position that they may fall into the trench. Rollers must be used during the laying of cables, ensure there is no any sharp projecting parts liable to damage the cables.
After complete back filling it would be clear and level the works so that the finished reinstated ground level shall be the same as that which pertained prior to commencement of the works.
Cable Damages During Excavation & Installation
The servicer must take all reasonability and precautions to avoid any damage to buried services, existing surface and other encumbrances land, property, roads, fences, walls, gates any kind of public or private property or environmental issues, and must ensure that the work is adequately supervised, so that unavoidable damage is reduced to the minimum. The work servicer will be liable for all damage arising by or in consequence of the works and should pay compensation. After complete the installation job, of course remove all spoil and surplus material from sites.
Consider the following facts that often damage the cable during excavation and installation:
Consider existing underground power line, communication line, gas line, water line and many more utility services hidden underground;
Consider any metallic or sharp object may be hidden in any place;
Handle and shift the cable drum carefully to avoid cable damage;
Use proper jack to lift the cable drum;
Use sufficient roller to pull the cable, special bend roller must used in curved trench;
Remove stone, chips, or any foreign materials from trench before cable pulling, cover up by sand as soon as cable cable pulling completed;
Don’t apply too much tension to pull the cable;
Take special care at road crossing point during cable pulling;
Don’t ignore any suspicious or theft possibility.
Thrust Boring, Heading and Tunnels for Cable Trenches
It’s often to face road crossing, rail line crossing, drains and canal crossing during trench excavation for power cable installation. These crossing should followed some especial roles and conditions as per international and local codes.
Work on thrust boring headings or tunnels shall be carried out as an adequate instruction. It should take all reasonable steps to ascertain the position of all sewers, drains, pipes and structures and these must be recorded on a drawing showing the cross section and levels or the proposed works before operations are commences.
Thrust boring just a blind job, so must be ensure there are no any utility services or not affected during carry out this job. Especially cable crossing a rail line, thrust boring is necessary.
Obstructions for Cable Trenches Excavation
When in the course of the contractor works obstructions are encountered which necessitate diversions of or alteration to other underground works or alterations to buildings or foundations or when conditions necessitate the adoption of a special form of trench the contractor shall immediately notify the authority engineer further work shall not proceed until written instruction have been obtained from the authority.
Excavated Materials for Cable Trenches
The material excavated from each trench shall be placed so as to prevent nuisance or damage. Where this is not possible, the excavated material shall be removed from the site and returned for refilling the trench on completion of laying. Surplus material shall be disposed in adequate way that will not harmful.
Disposing any level of hazardous materials should follow the local or international hazard disposal rules.
Cable markers of an approved type shall be provided along the route of buried cables as required to reinstatement is being carried out. Markers shall be installed vertically over each cable at maximum 50m intervals or any requirement at all road crossings and joint positions.
Cable route and joints marking can reduce the operation and maintenance time during any fault occur, as well as help to future plan for other utility company visible the existing cable route.
Protective Cover for Cables
To protect the installed cable from any damages, protective covers shall be made of RC slab each 75 mm thick, 300 mm wide and length as required or any especial measurement and protecting materials .
Warning also be put along the trench over the protective slab that will ensure warning, there are power cables just bellow.