To mark out a kerb line, engineers hammer metal pins into the ground. Then, they wrap electrical tape around the pins. When string is wrapped around the top of the tape, the string line dictates the line & level of the kerb line (see photo no.1 in attachment).
This is the fundamental method but it introduces risks. The first is the risk of the hammer missing the top of the pin and smashing into the worker’s hand, which could easily break bones. The second, more serious risk, is the metal point piercing an electric cable. This practice has caused several serious, even fatal injuries in the past, yet we still do it.
We experimented with placing sockets just above the ground and fixing the socket to the ground with in-situ concrete. When the concrete sets, it will have glued the socket to the ground. Then, removable plastic tubes can be inserted into the sockets, so line and level can be determined.
If the site is well organised, it should be possible to use concrete that would otherwise be thrown away thus reducing waste of concrete. This process has been used successfully on site – see photos 2, 3 & 4 in attachment. Chris Underwood, R Clifford & R Leivars carried out the installations and experiments, with the support of I Bingham, R Chattoe & P Insley.
As the plastic tubes can be reused, this system is more environmentally friendly. ‘Permits to break ground’ are no longer required so sockets are quicker and we estimate that on a £25 million road job, there will typically be a saving of around £9000 because instead of spending £12000 on pins, £3000 would need to be spent on Sockets. More importantly, the system is much safer because there is no ground penetration, so the risk of service strikes along with the risk of serious injuries has been eliminated. A UK patent has been applied for.
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