Go BottomTrench Bottoms
 | TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-05-26 28593
There seems to be some interest in back hoe operation so I thought I'd comment. The thing that took me the longest to get the hang of is keeping level trench bottoms. I’ll describe what I do, and maybe somebody has another techniques. The problem is that you dig by pulling the dipper back, but the dipper moves in an arc. If you're digging with long strokes, you get a scalloped trench bottom. In addition, there is a 'best bucket angle' for digging. The bucket angle changes as the dipper moves through its arc and becomes wrong unless corrected. However, correcting the bucket angle makes the scalloping worse. I have two solutions. The first one is to dig in soft soil, and then there isn't a problem. The bucket fills with short dipper swings, so scalloping isn't a problem (and not good to drag full buckets). In harder earth where the dipper strokes are long, I start the dig, and then 'bump' the curl to increase the bucket angle and almost immediately bump up the boom to raise the bucket. That manages to keep a fairly level trench bottom. It does take a little practice to coordinate the three functions, and it's probably easier with some loader controls than others. However, the practice is worth it. The first several trenches I did, I ended up walking the trench bottom with a hand shovel to even it out. I don't really want that job.
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| Paul Fox
Join Date: Posts: 1 
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2001-05-26 28599
Clean trench bottoms do take some finesse. If it's critical (like say, for a footing or a formwork trench), I'll usually dig a little too deep, and then knock some loose stuff in and drag the bucket over it to smooth it out. Otherwise, I can usually coordinate the boom, crowd (aka dipperstick) and curl to keep the bucket angle where I want it and "sweep" the last couple of cuts and get a pretty clean bottom. That's where joystick controls really shine. ....
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| droz
Join Date: Posts: 1
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2001-05-27 28619
Of course, if you are doing a footing, you do not want loose soil underneath so you don't want to dig any further than necessary. Backfilling a footing trench is frowned on. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-05-27 28635
Droz's comment should be noted as good advise for us novices. I don't think I'd tackle footing trenches with my present skills for those reasons. Frowning inspectors don't inspire much happiness in me. I imagine Paul is talking about minor variations, and gee a smooth trench bottom does look good. I'll have to remember using the bucket bottom to smooth out the bottom. The controls on my Kelley B600 are combined boom/swing on left and dipper/curl on the right with two stabilizer controls in the centre. I haven't used the hoe since late summer, but the way I remember is that the combined dipper/curl makes it possible to smoothly adjust the curl almost without interrupting the dipper stroke. I believe the boom is first in the open centre flow and takes precedence over other functions. Pulling the boom up while holding the dipper on seems to stop the dipper until the boom is released. Small up adjustments on the boom can be made by short 'pulls' on the boom control. I haven’t seen other tractor hoe controls so I don't know if there are more convenient types. I am trying to think through whether a self-leveling bucket, similar to some loaders, would work or not. ....
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| Paul Fox
Join Date: Posts: 1
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2001-05-27 28638
Point well taken on footing trenches. I picked a poor example. I've only done one foundation trench, and it was in sand fill, and it was a nightmare! The few times I've "cheated" on a smooth trench bottom was for sewer lines, where consistent pitch was important. My apologies to anyone who was misled by my poorly thought-out post. ....
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| By the Brook Farm
Join Date: Posts: 1
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2001-05-27 28649
Quick question re: footings. Why would the bottom of a trench that is going to have a footing poured in it be considered "critical"? As long as it was the proper width and depth, what difference would it make if there were minor differences? As long as the top of the footing was level who cares what the underside of the footing looks like. I understand the need for virgin gound under a footing. The reason I'm asking is that I will be digging one in a few weeks. Once the concrete was poured, you could level the top of footing, maintaining a minimum thickness and elevation. What am I doing wrong here? ....
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| droz
Join Date: Posts: 1
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2001-05-28 28660
Well, of course, it doesn't really make any difference if there are variations, except that if it is a footing depth of 8 inches in one area and 12 inches in another (I don't know how thick the footing will be), you will be wasting a lot of concrete. But your are right in that the surface will be level. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-05-28 28669
I think that variations would complicate applications where re-bar is used, but I don't know if building codes would apply. However, I guess I should figure some of this out before trying to get a permit for a bathhouse at our camp. I've got a much better grasp of electrical codes than building codes. Maybe there's a 'building codes made simple' book. What I do know is that I'll have to mix the concrete using water from a not very productive dug well, or truck it from a river. I can just see myself with the work half done and a mixer full of half-wet concrete and then the well goes dry. Yikes, I don't even want to think about it. I'll have to be really fine with the footings trench, or slab-on-grade leveling. Wasting concrete here could be more than just a cost aggravation. ....
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| JeffM
Join Date: Posts: 1
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2001-05-29 28709
TomG, after many hours of practice I can finally get a flat trench bottom with a hoe or excavator, but I'll be dipped if I can effectively explain in words how I simultaneously use the boom, dipperstick, and bucket to accomplish this. Kind of like explaining in words how to swing a golf club - and after many hours of practice I still can't do that well at all. Think I'll stick to backhoes and loaders. :>) ....
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| ashley
Join Date: Posts: 1
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2003-02-25 49945
i run a 5T excavator i pick a mark on the boom just above the bucket at the right depth and keep it in line with ground leavel, practice running bucket teeth 2" above ground without digging through the full boom swing ....
Link: ashley
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-02-25 49958
Well say, an old discussion returns. The bathhouse, that I'll now call a washshed going back to my days of visiting the farm, has been in use for several years now. The carpenter who did most of the building still calls it our oriental bathhouse though--because it's on stilts, has very wide eaves and high windows. Sort of gives the idea a different meaning than calling it a washshed, which of course the carpenter if fully aware of.
I haven't had to do much more trenching since then so I don't know if my bottoms would be any flatter (I have spent quite a bit of time sitting here writing stuff though). At the time I was aware that some hoes have coordinated controls that are supposed to help with getting flat trench bottoms. I have no idea about the merits of coordinate controls except that they probably take a bit off the power specs.
Since then I discovered that my hoe has a float function on the boom. I suppose that's a common feature--I just didn't know about it. I haven't experimented with it yet, but I suppose that setting the right bucket angle and then pulling the stick back with the boom in float might make help make flat bottoms.
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 | jeff r
Join Date: Jul 2003 Posts: 428 burton. michigan
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2003-03-16 51246
HEY TOM,
How does that full float feature for the boom on your backhoe work? Is it like the detent for floating on a FEL? ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-03-16 51251
Jeff: I discovered the float while the guy with the pump truck and I were trying to figure out our very unusual homemade septic system. It wasn't a good time to experiment and I haven't used hoe since.
I did find the detent by accident (I might find that more thorough readings of manuals does wonders). I believe it works exactly like a loader float. I'm expecting that in float I might be able to finish trench bottoms using the float and pulling back the stick with occasional curl adjustments. The float might take the tendency to dig deeper as the bucket gets closer to the tractor unless the boom is pulled up periodically.
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2003-03-16 51253
I dig the same as Ashley, I pick out the depth on the boom or bucket that I need and then look between the grade and the imaginary mark to dig a level bottom. ....
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| Ted at Abbeywoods, L
Join Date: Posts: 1
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2003-03-16 51279
Regardless of the machine, be it a backhoe or an excavator, the imaginary mark method works well for level ground. But for ground that dips and swells you can't beat a laser. I find my Berger/CST LM30 to be indispensible for excavating. Unlike a transit, it works with just one person on the rod, so once the laser is leveled out and is set to 360 degree or sweep mode I can hit grade with little guess work. Make your cuts high, check the grade, dig down the depth you recorded high. You'll be right on with a little practice. Bright days require the special glasses to see the laser beam on the rod, or use the laser sensor with audible signals. These units have come way down in price and are valuable for excavating, trenching, grading, survey, etc., and they don't take long to learn how to use. For the record, some uneveness is common even for pros, and only a total jerk of an inspector will rain on your parade by shutting your dig down. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-03-17 51309
For people who haven't trenched much some of this discussion may sound mysterious. We've been talking about the solution, and I'm with JeffM's comment that I can do it but I can't say exactly how. Trenching like grading is an acquired art.
The problem is that the stick rotates in a arc around its pivot point on the boom. Most digging is done by pulling the stick back. If the stick is ahead of its pivot, it goes deeper but the bucket angle becomes less aggressive. Sometimes just changing the bucket angle keeps the dig the same depth and other times I have to pull the boom up a bit and and adjust the bucket. I think it depends on how far the stick is out to start with.
For my grading last summer, I used a water level, string and two heavy lighting stands from my sound/lighting buz days. A little arithmetic gave me the drops I needed for particular grades. I put one stand at the top and the other at the bottom, measured the water columns in each and dug or filled the bottoms to get the right drops. Then, I'd tie a string between the two stands the same distance above ground level. The string would then be at the grade angle. The string should be the same height at any point along the grade.
A laser level with a vertical probably would make things easier but I bought plastic hose for the water level before I noticed how inexpensive laser levels are. However, the inexpensive ones didn't seem to have verticals, which means I'd have to calculate a drop for each point checked along a grade. Somebody probably knows an easier way. Even if I had a laser, I'd still use the water level for checking drainage paths around buildings.
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