I had to abandon my leach field and septic tank in my back yard as the leach field was saturated and the city would not let me replace it as a city sewer lime connection had been stubbed out onto my property. To make a long story short, the connection to the city sewer line was made. The septic tank was pumped, collapsed, filled and covered up appropriately.
However, in the process my telephone line was cut. The telephone company replaced the line for no cost as the line was so old. The telephone companies contractor was supposed to bury the line more than 8" deep but I was to discover, in most places it was buried less than 3."
Although highly irritated, I was not willing to hassle with the telephone company and decided to bury it myself and this time at least 12" deep. This would allow for digging and rototilling without worry about the telephone line.
I strung string lines where I wanted the telephone line to be placed parallel to the house and along the side to the telephone box on the wall. I borrowed a friends 2400 p.s.i. high pressure washer and wrapped red tape around the washer wand 14" from the tip of the wand to assure the trench would be a minimum of 12" deep in all locations.
With good leather boots on, a rain suit bought at Home Depot on, a full coverage face shield also from Home Depot on, I used the string line as a guide and with "pin point" tip on the high pressure washer I began to "water blast" the trench making several passes to blast the dirt (now mud) out of the trench to the depth of not less than 14." Using the red tape on the wand as the gauge for minimum depth.
Although I had not given it a thought when I began, it was nice to find out that major roots of the many pine trees could simply be plasted out from under the roots and I ran into several lines of various kinds which I would have cut had I used a trencher but were left untouched by using a high pressure washer.
In just over a day I had my trench the full depth I wished, minor roots I didn't care about were cut simply by using the high pressure washer to cut them. Major roots, a fence, pipes, and lines were not damaged but were tunneled under with the high pressure washer. The most important thing to me? I never even touched a shovel nor used any other tools. As I have a heart condition and have multiple sclerosis this would have been a daunting task to say the least.
The following day the mud and water had mostly settled down and I disconnected the telephone line from the box on the side of the house and simply "threaded" the telephone line in the trench, under roots, pipes, lines, fence and reconnected the telephone line to the box at the house. I might mention, I did run into a few rocks and either blasted around them and removed them or blasted under them or simply went around them.
I then used a 1" X 4" to push the telephone line down to the bottom of the trench making sure, at no point, was the line less than 12" underground. Using a wider angle tip on the pressure washer I then washed the dirt (mud) back into the trench using a sheet of old plywood set on edge right next to the trench to act as a backstop for the mud so the mud had to be concentrated at the trench line. I did this on both sides of the trench; thus, the mud was concentrated directly in and over the trench.
Added bonus to this method besides not being at all laborous was the mud of course compacted the trench full. Once the mud completely dries out I can run over the remaining hump above the trench with my garden tractor and then spread the small amount of excess with a yard rake.
Downside? One looks for all the world like he or she has been rolling around and playing in the mud in a bright yellow rain suit while doing the job. But, hey, high pressure wash the boots while still on, strip out of th rain suit, take off the face shield and one is as good as before they ever started with the job. Hang the rain suit and face shield on the fence and anything else that needs it and high pressure wash the whole works to like new appearances.
I might mention, while doing all the above things get mud splattered everywhere but not to worry. Simply wash the mud off with the high pressure washer as you go, repeatedly if necessary, plants included, no big deal. Just vary the distance and tips used on the washer so as to not damage anything. Changing tips back and forth takes only seconds.
This method also works well when installing a sprinkler system in an existing lawn as well as an unplanted lawn or garden area. Simply use a gas driven lawn edger with a new edger blade. Use a string stretched a close distance from the trench you wish to cut. Run the edger along side the string with the blade set deep enough to cut clear through the sod up to about 3" to 4" deep and then do the same about on the other side of where you want to run the sprinkler pipe. About every 12" to 18" cut across between the cuts you made which are on each side of where you want the sprinker pipe to facilitate using a narrow (4") shovel to lift the sod out of the area you are trenching.
Now spread a minimum of 3'0" of 4 gauge or thicker strips of black or clear plastic on each side of the proposed trench and lift out the sod from the trench you have cut and lay it on the plastic about 2'0" from the trench. This will hold down the plastic and hold it in place.
Take some cheap, really cheap, paneling, plywood, hardboard, or any other sheeting and cut them into 8"0" by 18" strips and then nail them to some old lumber such that the sheeting will stand vertically. Most likely you will need to nail some kind of angled bracing to prevent them from being blown over by the blast of the high pressure washer. I recommend making at least 4 of these so you can move them forward as you blast your trench. But don't make a "federal project" out these "shields" and don't make them to heavy as you will want to move them forward as you go.
Now with plastic spread immediately adjacent to each side of the proposed sprinkler line trench, sod placed on the plastic far enough away from the edge of the proposed trench, (for working room and "shield room) place the shields on each side of the trench, about 6" away from each side of the proposed trench running parallel with the trench you are nearly ready to "dig" your sprinkler line trench. However, experience has taught me it is best to cut some 2X4 or 2X6 blocks about 24" long and cut slots a little wider than that thickness of shield materail. Cut them really deep into the 4" or 6" side of the boards, such that they when you place them spanning the distance you placed the shields on each side of the proposed trench they will be able to push them down on the shields and this will prevent the shields from being "blasted" apart when "high pressure washing" (blasting out your trench). Place these "spanners" down low at the beginning of your shields, the end of your shields and a couple on the top of the shields. DON'T NAIL THEM TO YOUR SHIELDS, this way, as you move along blasting out your trench, in minutes, you can advance your shields and spanners as needed.
I have found 4 of these shields are best as you "trench" rather quickly and if you don't have 16'0" +- to work with to "leap frog forward with your shields, you wind up blowing mud all over as you near the end. Plus you have nothing to make your right angle corners of your trench.
Once you have done the above, and understand the above, you can "high pressure washer blast" your trench as deep as you wish and "go ahead on!" the shields being 6"+- away from each side of the trench pretty well confines the mud to right next to the trench. Mud is not being splattered all over the place and is 90% on the plastic. I always overdig a minimum of 2" so I don't have to worry about cleaning out the trench to get the desired depth. One can make several "V's" with heavy wire coat hangers with the tops of the V having 6" or more on each side of the legs of the V to hand on each side of the trench such that the bottom depth of the V to the top legs of the top of the V is the proper depth you want the line buried to if you are really concerned that the pipe might be buried too deep.
Once you are done "high pressure washer trench blasting" you have a trench deep as you wish, as wide as you wish, as long as you wish, in a pattern you wish, with mud on top of plastic sheeting, sod on top of plastic sheeting, and maybe a little mud splattered where you don't want it. Well, wash it off if you didn't do that as you went.
You are now ready to install your sprinkler system piping, or conduit, or direct burial electrical lines, or, or, or, or. Go for it and have a great time.
Once you are done with installing whatever you are installing simply use a wide angle tip on the high pressure washer and wash the mud back into the trench(es) or if you must, you can shovel it off the plastic back into the trench. Not me, I am too lazy! With a little practice one quickly becomes an artist with a high pressure washer. Besides, with a high pressure washer, the mud settles and conforms to whatever has been installed in the trench and compacts solidly around it.
Remember the sod has to go back into the trench so backfill with the high pressure washer accordingly getting the depth just right to have the sod at the proper height. And please don't do what a friend of mine did when I did this for him, actually he helped me do it. He thought it would be real neat to fertilize the soil just before the sod was reinstalled. No problem telling where his sprinkler lines are, the prettiest green stripes all over his lawn resulted from his bright idea of fertilizing the trench!
With all of the above done, simply replace the sod in the trench exactly as it came out. Hopefully when you laid the sod on the plastic sheeting you laid it butt to butt exactly in the orientation it came out of the trench. Once this is done it is time to wash the plastic off and blow what mud is left into where the trench was.
Pull up the plastic and do whatever with it. now you have sprinkler lines, a sprinkler system, sod grass back at proper place, at proper height and still some mud. And Oh-Yeah, probably some real yellow grass where the plastic was. Not to worry! with a wide angle tip on the high pressure washer AT A DISTANCE from the grass slowly wash the mud first into the cracks around the sod and around the PROPERLY PROTECTED AND COVERED OVER sprinkler heads. Without damaging the plants or grass or anything else carefully wash the mud down through the grass such that you no longer see anything but green grass and sprinkler heads.
Speaking of heads, if you wish to keep yours, I would survey the whole area and make sure you have washed all the mud dirt, debris off of everything the "little woman" will be able to find or see. As you probably well know the good thing you just did in this project is non-consequential as compared to that spec of dirt or mud that you may have gotten stuck to the muffler of HER S.U.V. and you will never hear the end of THAT!