Trench Rescue Techniques

Although I've got my own ideas, how does your agency approach the shoring of "L" trench intersections? Please describe! Thanks.

If the trench is narrow (less than 4 feet wide) at the "L" we would probably do the following:
With FinnForm panels inserted on both sides of the L (two panels on each outside leg of the L and on on each inside leg of the L) we would insert walers on the outside leg then pressurize the struts so the contact point on the inside of the L is about 1 foot from the corner. Spacing from top to bottom of the trench is usually as follows: 1st strut @ 2', remaining struts 4' apart and last strust within 1' of bottom (giving us at least 1 foot of digging before we have to reshore).

One important point: The struts opposite each other on both sides of the L need to be pressurized at the same time so not to blow out the corner.

We do not, as a rule, put any struts in the corners or countersink the walers into the soil. We have nailed the FinnForm for the L's inside corner together with a 4x4 so loose dirt does not fall out.

If the corner is large, say much wider than 4 feel I'm not sure how we would shore it as we lack immediate resources for such an undertaking. A lot of times I see trench boxes on site but not in use so perhaps we would try and use the trench box somehow.

If you were looking from the top at the trench (like it was an "L"), heres how we would normally do it.
On the panels which sit on the upper inside of the trench(both legs of the "L") there would be "thrust blocks" attached to the panels. These blocks are 6x6 lumber with 45 degree cuts at each end and a channel cut in them to fit over the strongback (2x12). They would be attached to the panel and at the level where each strut would be placed and shot.
The panels which are in the bottom left corner of the trench would be "free floating" at this point. Whalers would be lowered into position and corner blocks would be fitted into the lower outside corner (again at each point where a strut would be fired). From the thrust blocks on the upper inside set of panels, struts would be positioned and fired into the lower corner of the trench to set the corner panels (the strut bases rest acainst the angled end of the thrust block and shoot diagonally across to the outside corner). The whalers would also be secured with "cat heads" or struts to finish off the system. If the trench was oddly shaped (most are) voids are filled with low pressure bags, cribbing or backfilled. Supplemental shoring is fitted as digging lowers the trench floor.

[This message has been edited by e33 (edited April 23, 1999).]