Most Cost Effective Way To Do Some Significant Trenching?

[NutCutter]

I am but a simple Aggie...so I need lots of help!

We have to 'redo' the soil on an established orchard. The essence of this means that we have to dig a trench with a minimum requirement of 40” (Ideally 60”) wide by 14 ft deep (Ideally 18') by about 550,000 ft long. We have to get the trench to within 10 ft of the existing tree lines. The soil dug out will be mixed and dumped back into the trench from which it came. Would like to complete this project in less than two years from now.

Any and all suggestions as to the most cost effective, easiest and quickest way to go about tackling this project would be greatly appreciated!

 

[speedy]

18' deep will require 1:1 sideslopes from a point 3 to 4' from the bottom of the trench (OSHA requirement) if you are going to allow men on equipment in the trench. You could use remote controlled compaction equipment to get around this. Although I don't know of any off-the-shelf large compactors to handle this task, but there could be custom units out there, or they could be rigged up rather easily, the technology is out there. (remote-controlled units I've seen are generally in the 24 - 30" wide range) Compaction will be required or the dirt will not fit back into the cut. The dirt will 'fluff up' by 30 to 40%.

You will undoubtedly encounter many large rocks that you will have to haul off-site. That is a hell of a lot of dirt, and will likely require that spoil piles be placed on both sides of the trench, this will add to the instability of the trench sidewalls. You will likely want to have some degree of sidesloped or chamferred walls anyways as opposed to vertical walls.

As for equipment, I forsee a rather large excavator with a 36 to 48" wide bucket. 2 loaders to backfill (one on each side) and 2 RC vibratory padfoot compactors working to fill the trench in 6 to 12" lifts with 3 to perhaps 5 or 6 passed to get density on the material. The process of excavation, piling (on one side the the other, successive bucketfulls), backfill and spreading the soil in the trench should do a pretty damn good job of blending the soil strata. The top width of the trench and the space requirement for the spoil piles on each side of the trench, (with loose dirt (140% of the unexcavated, in-place volume) and a 2' set-back distance from the edge of the excavation to the toe of the spoil piles will require a good deal of width, this could be minimized somewhat by a continuous, almost factory-like- JIT (Just-In-Time) process of backfilling may reduce the space requirements to some degree, just how much less??? I wouldn't hazard a guess, and may require more compactors or other in-trench equipment to streamline the process.

Sounds like a hoot!! What have other orchards done to accomplish this?

 

[JDOFMEMI]

Speedy: Not so fast. You have made a lot of assumptions about a project we know little of.

Nutcutter says nothing of compaction. In fact, he is talking about an ag project, so it is likely to be no compaction. Also likely to be no men in the ditch. He also talks of mixing the soil, maybe fertilizer or some kind of ammendment? That will create more volume if it is the case, so does it need hauled off, or just spread out?

Also, about the 10' from existing treelines, is that on one side, or both? Makes a huge difference. We also know nothing of the soil type. Are there rocks? caliche? hardpan? sandy soil? I would like to know some of these particulars before reccomending an equipment spread for the job.

With a few more details, Nutcutter will get a much more detailed response.

Another good question is what time frame would you like to complete it in? Finishing in 4 months is a different deal than finshing in 2 years, for example.

About the mixing, what is involved? Balancing the operation depends on knowing what the limiting factor is. Is it trenching, mixing, backfilling, obtaining the mixed in material, or something else. It does little good to trench 550,000 ft of ditch in 3 months only to find it takes 2 years to get the mix and fill it up. Again, times just for sake of example.

 

[Scrub Puller]

Yair . . . As JDOFMEMI says more details are needed. I know a little about orchards and can't imagine what the object of this exercise is.

Questions for NutCutter...

1/ Are we digging between rows of existing trees? If so how high are the trees how wide are the rows and what is the in row spacing.
2/ What is the material, how well does it have to be mixed and will we end up with a surplus.

That's just a couple of points for starters . . . it will be interesting to see how this develops.

Cheers.

 

[speedy]

1,426,000 to 1,833,000 cubic yards of material (in-place volume, with no allowance for any cutback) and backfill. I don't think the job is an affordable for an orchard, even if it were growing oil. I'm curious to see if the OP sets out anymore details.

 

[NutCutter]

I want to thank everyone so far for chiming in!

More info:

To clarify some of the questions raised:

We are not growing oil!!!!!

This is for an existing orchard.

The spacing on the trees is 30x40'

The issue is that there are salt build ups that are detrimental to the trees. The way to break that is to, in essence, turn or mix the soil. That will allow the salts to be released.

This is a mix of soils which is predominantly one form of clay or another on top with sand below.

We do not have to add anything to the mix

What comes out of the trench goes back in the trench...just as long as it is not put back in the way it came out.

To get to the sand varies in depth from 2-3' to, in a few areas, deeper than an excavator can dig. In my experience we usually have to trench in the 14-16 ft range to get that mix that is needed.

There will be no entry into the trench for any reason.

Yes, I know this project is expensive...it is more expensive to NOT do this.

A little background:

We have traditionally rented a John Deere 250 or similar sized Excavator about four weeks a year. We have been trenching center lines in our most problematic areas. While this has helped, it turns out that, in looking at the way in which this soil releases the salts, we have not been nearly as effective as we should be. Thus the requirement to be with in 10' of the tree line is to address and insure that the trenching is actually beneficial in releasing the salts in the zone that the trees need.

I will attempt to describe what the most efficient way for us so far has been:

When we start a trench, we are in line with where the next trench will end. So the first bit of dirt we dig out we place as close to where the next trench will end as possible. That creates the plug that we will finish filling the next trench in with. This setup creates a condition in which the only time we actually swing the machine is on the ends to start the trench and to finish filling the trench.

After we get to a certain point with the hole that starts the trench we advance the machine towards the hole, pull towards the machine the top half of the soil into the bottom of the hole, and then pull the bottom half up and dump it on the top of what was the top soil. The dirt never really leaves the trench. This actually does enough mixing within the trench to meet our requirements. We do not have to swing the machine. The trench is backfiilled as we move across the orchard. The only hole or open area into the trench is within the reach of the excavator. The excavator itself is actually advancing over the already backfilled trench. With a 36” bucket on a 250 sized back hoe diigging in the 14-16 ft range I think we have averaged about 175' linear ft an hour (I calculated it out once...not smart enough to have written it down though). I also have it in my mind that my total cost to do this style of trenching is running about $.35/ft with the rental, fuel and labor.

The ten foot requirement is going to be hard on the sheet metal and bits and pieces of the excavators. The trees usually win.

Right now my plan is to trench two lines in every other row...all trees would be trenched on one side in year one and then the following year trench the remaining rows.

Excavator Options I am considering:

Renting: and paying the damages as we go.

Buying two late models off a rental fleet...something in good condition in the under 1200 hour range and then selling the residual when done.

Buying new, and then selling the residual when done.

I think I am looking at 3-4K hours of machine time for this project...so I am leaning towards the last two options.

One other problem is this type of work is tedious and boring. It is difficult finding operators with the right mix that can do this type of trenching all day, every day, and stay efficient. I actually consider this the biggest challenge to the project.


All that said:

What am I overlooking? Is there a more efficient, cost effective way of tackling this than what I am currently thinking?

One of those really big trenchers such as the T1255 put out by Vermeer and then backfilling with a dozer?

Something else? I don't know! I am looking for options as well as critique of my current approach.

Thank you.

 

[speedy]

I would have thought that installing conventional drainage tile would be the answer, but if you can mix the stratified layers of clay and underlying sand and improve the permeability without installing an 'unnatural' failure-prone man-made system and then having to deal with the water collected, which would be a disposal issue as it's high in soluble salts, it seems like the best option. I think you have a pretty good handle on what you want done, how to do it, and the costs involved. I have a question though, How much settlement do you get in the deep trenches over the years if you don't at least try to 'tighten up' the backfilled material?

 

[JDOFMEMI]

Nutcutter:

Thanks for the details. We all have a more clear picture now of what you are looking for.

With the new information, my thought runs toward a ladder trencher. The common ones are wheel type, but they are depth limited. A ladder trencher can be run with a boom to dig 18', and do it much faster than an excavator. The best part about it would be the continuous mixing of all the soil layers as it is dug. With soil conditions like you have described, and with the production you quoted of 175' per hour for the excavator, I would not be surprised to see near well over 500 ft per hour with a good sized trencher. The hourly rate will be much higher, but production should make up for it.

For backfill, a mobile conveyor arrangement could be rigged to follow the trencher, and belt the material at an angle back into the ditch. Then you would only have a small pile at each starting point that could be rehandled with a wheel loader or something.

 

[Dozerboy]

I agree with Jerry look into a trencher it would do the best job of mixing the soil.

 

[quantum500]

I'm interested in what the end result is? What are the salts? Why can't you leach them out? Have you looked into a microbial solution? What is the ph? Seems to me there is a simplier more cost effect solution available.