I can only describe it as a jig, at best. It looks like as if it were home-made from scrap iron. Driving by slowly, it appears to be two, parallel steel plates separated & supported by two or three cylinders. The cylinder diameter is maybe 6-8" and 3-ft in length. Thus, the two plates are roughly 3-ft apart.
The steel plates are roughly 4’x8’, as a guess. I WAG it is support the trench walls, but it is so short, of what use is this thing? Also, I have seen a back hoe drag this thing, but I highly doubt it actually cuts the trench…it is too blunt. One last thought, maybe it is soem kind of guide by which to measure the depth of a trench to keep it at some constant elevation???
What is this thing, what is it technically called, and what “nickname” might it have by the construction workers, if any? Just curious…
It does indeed sound to me exactly like the devices used to support trench walls whilst men are in the trench. In my former life as an engineer I saw things exactly as you describe used for this purpose all the time.
The cyliders between the walls are probably either hydraulic or screw rams to hold the walls aprt… the gap between them is therefore variable to suit the trench width.
I guess it is short because it is used in pipelaying, where perhaps only the section of trench at the join, where men are working, needs support?
What you saw sounds like SHORING, which is just bracing installed on a trench to keep it from collapsing. This is largely a safety precaution, since trench collapse is a real hazard to wokers laying underground utility piping.
I am more familiar with wooden shoring. And, then there’s wooden forms for pouring cement. I guess the metal design is more versatile and more practical than wood in many ways…
It’s called a trench box, and is indeed used to support the walls of the trench. OSHA rules require some type of shoring for trenches deeper than 5 feet (or shallower if the walls are unstable).
Based on the description provided, they are indeed called Trench Boxes. But they are not shoring or bracing, but rather shielding. Shoring or bracing attempts to put pressure against the trench walls to prevent the wall from collapsing. Shielding does not prevent collapse but simply protects the workers in the case of a cave in. Shielding is typically much heavier duty than shoring.
Looked like it was too short to do any good? Possibly, hard to tell from your description. Trench boxes are often used in non-OSHA approved ways. OSHA wise, the boxes should be stacked if not close to the top of the trench, close to the top of the vertical walls, with the remainder of the walls sloped away from the box. However, trenches generally collapse from the bottom, not the top, and workers know this. So since it is a pain in the neck to move a stack of two trench boxes, often the top one is forgotten.
Unlike shoring that is intended to keep a trench open for some indefinite period of time, trench boxes, as BoringDad noted, are simply used to protect a worker in the trench from cave-ins on the worker. The small size coupled with the mention that it was dragged by a hoe suggests that that particular trench box was being used at the head of a water line or some similar installation.
The trench is opened for the length of one section of pipe ahead of the trench box. The new pipe is laid with a worker handling the coupling of the pipe sections from within the trench box, then the box is pulled forward over the just laid pipe and the hoe begins excavating the next pipe length. Meanwhile, the newly laid pipe is reburied behind the trench box.
Trench boxes can vary widely in size. Some are double-walled plates that are 10 feet high and 24 feet long and the separators can be anywhere from four feet to 16 feet long (wide). (They may get bigger, yet, but I have not encountered any larger than I have described.) There are also narrower and shorter boxes that are welded into a single unit for strength when they are pulled through the trench on a daily basis. (The larger ones come as separate plates and spacers and are matched to the sizes needed for a particular pit or trench.)
