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Show Learners |
- Trench Shoring Tables – using shoring tables what
shoring is needed for following trench excavations? a)
shoring – no wales; 11’ deep, 3’-6” wide in soil likely to
crack crumble. b) 3.8 metres deep X 1.3 metres wide in
stiff/firm soils. c) 9’ deep and 6’ wide in loose soft soils
– can’t shore this one because excavation wider that 5’.
When using trench jacks, stress point that jacks can only
extend according to manufacturer’s specifications. Max
ratio of 2:1 of length of jack outside of pipe to amount
inside of pipe. (an 18” screw jack can only be extended
12”) It is recommended that the extension ratio should
be only 1:1. Make sure when jacks are placed against
uprights or wales that the jack foot is placed across the
grain of the wood – not parallel to the grain. This could
cause the foot to punch through the upright.
- Installing Wood Shoring – the first or top strut is always
placed/installed from outside of the excavation. The
upright should extend 1’ past the top of the excavation.
Mention the fact that the worker who installs the struts
should be the one that removes them. This is so if there
are changes in the pressure on the struts, the worker that
installed them will most likely be familiar or remember
how the struts went in and will recognize if there has
been changes in pressure on the struts since the
installation was done.
- Sloping Excavation Walls – when determining the
width of a sloped excavation use the following formula:
fully sloped at 45 degree angle: 2 times the depth + the
width. Example – an excavation 12 feet deep and 4 feet
wide will have to 28’ across at the top. If the excavation
is sloped at a combination of 3’ vertical and then sloped
at a 45 degree angle, the formula is: depth minus 3’
times 2 + the trench width. For the same excavation
above, by using the combination straight cut and sloped
the width across the top of the excavation is now 22’.
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