Installation of Water Pipe

If it is for safety, it will say the slopes shall be required at a certain depth. Since I see "most" of electrical trench excavation are done without slopes.

Good Morning RHK,

In my local, we call them "Drag Boxes".

Good morning, and thanks!

Old Coal Man calls them "trench boxes" which is another good name. (I guess I never heard a name for them, just saw them in use--although I probably read the OSHA regs--I wonder if they used a name there? Oh, well, no big deal (meaning I won't go and try to find / read the regs). ;-)

In addition to the safety aspect, the width at the bottom of the trench allows the correect amount of "bedding" material to be installed around the pipe to prolong the service life. Sloped sides in this situation also help to direct the material to the bottom around the pipe.

Electrical instalations usually install a conduit with the wires loose inside this. Thus the conduit is providing the mechanical protection for the wires.

A trench with sloping walls that is say 36" wide at the top requires less material to be removed if the same trench had straight parallel walls. The trench needs to be wide enough for a man to work in.

I worked on a project where we installed stop lights at existing street intersections using the narrow vertical walls method to lay our 3" electrical conduit, The trench was 6" wide and 36" deep, this was done to minimize the amount of road bed we had to tear up. It was not a fun job, no room to use wrenches, only a rope for tightening the pipe, ambient temp. was 90°(+) asphalt temp.130°(+) and that's not including the temperature of the pipe, which was laying in the sun! Which required a lot of sweat, and water with a dash of gymnastics to avoid the people who were trying to run us over.

It would have been nice to have nice wide open trenches with the required shoring and maybe a sun shade on top of it all.

I forget how deep a "Ditch Witch" can dig, but it produces a narrow straight-walled trench. The trench is too small for anyone to work in it, but one could accidentally step into it. For shallow trenches, this works well, but in cases where the trench must reach below a frost line (perhaps irrelevant in VietNam), sloped walls may be required. This probably depends on soil stability.

You did not mention process of joining pipe in the trench. It might be a water pipeline of cast iron which is being joined with jute and lead wool, it might be cement pipe joined with rubber ring abutting end compressed each other or it may be of a cement pipe joined with collar and cement. All these pipeline require 95% of compaction in the bottom of the trench. When pipeline is laid as described above, compaction under the pipe is not possible, only when trench is cut in slope. When compactor is run layer by layer, it shift earth/sand under the pipe and get compacted. For water supply pipeline trench bottom gradient is not made in slope, it is alway levelled to have the water drawing at equal pressure and flow to all consumer. Oil and gas pipeline does not require such design of trench, only where bedding or compaction on backfil is to be provided.

You can use vertical walls on a trench as long as it isn't deeper than say 3 or 4 feet deep (I can't find the OSHA manual). However, it also has to do with the soil you are excavating. A good loamy-clay will stand up much better than a straight sand. It also depends on the depth. Have you thought about using a trench-box. Many times, sewer mains are extremely deep, and contractors use trench boxes to support the walls as they work in the trench. You don;t give enough information with your question. Have you looked at any ground control books? What type of soil are you dealing with?