What is base preparation?
Getting the excavated hole ready to take a base can — trimmed, clean and dry, with a firm level bed, a way for water to leave and the cable entries in place — so the can sits true and the grout has a sound face to bond to.
Base preparation is the work done in the excavated hole before the base can goes in. The faces are trimmed and cleaned, a firm level bed is formed, drainage and cable entries are provided, and the centre and orientation are marked again ready for positioning.
The can takes its level and alignment from what it sits on. A can on a soft or uneven bed can settle or tilt, leaving the fixture out of level and out of alignment, and a hole that cannot drain can leave the transformer and connectors standing in water. Keep loose material out of the hole and off the surface, because debris on an airfield is a hazard to aircraft. Treat any cable in or near the hole as live until the circuit has been isolated, locked out, proved dead and earthed under the site’s procedure, and guard or cover the hole whenever it is left open, as the permit-to-work requires.
- Check the hole. Confirm size and depth against the design and clear anything loose.
- Clean the faces. Remove dust, slurry and loose pieces so the grout has a sound face.
- Form the bed. Place and level the bedding the design specifies, and check it is firm.
- Provide drainage. Form or connect the drain path so water can leave the base.
- Set up the entries. Position the duct or cable entries and protect any cable ends.
- Trial-fit and re-mark. Check the can fits, then mark the centre and orientation again.
Frequently Asked Questions
Q1What is base preparation in airfield ground lighting?
Base preparation is the work done in the excavated hole before the base can goes in. The sides and bottom are trimmed and cleaned, a firm level bed is formed, drainage and cable entries are provided, and the centre and orientation are marked again so the can can be positioned accurately.
Q2Why does the bed under a base can matter?
The can carries the fixture and its alignment. A soft, uneven or loose bed lets the can settle or tilt, which throws the fixture out of level and out of alignment and can crack the grout. The bed is formed and checked as the design specifies so the can starts, and stays, true.
Q3Why must the hole be clean and dry before the can goes in?
Grout and any bedding bond to a sound, clean face. Dust, slurry, loose pieces and standing water weaken that bond and can leave voids around the can. Loose material left in an open hole is also foreign object debris (FOD) waiting to reach the airfield surface.
Q4What is the drainage for?
Water can enter a base through the fixture, connectors or around the can. If it has nowhere to go it sits around the transformer and connections and can cause faults. The design usually provides a drain path or sump, and base preparation is where it is formed or connected, as the design specifies.
Q5How are cable entries dealt with during base preparation?
Ducts or openings for the primary and secondary cables are set in the position the design shows, lined up with the cable routes, and any cable ends already in the hole are protected from damage and water. Treat any cable as live until the circuit has been isolated, locked out, proved dead and earthed under the site’s procedure.
Q6What should be checked before the hole is handed on for can positioning?
Check size and depth against the design, a clean and dry hole, a firm level bed, a working drain path, cable entries in the right place, and the centre and orientation marked again. If the hole is left open, guard or cover it as the airport’s permit-to-work requires.
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