Mon Feb 24, 2014 5:43 pm
Connecticut Calvin wrote:
Barnyard wrote:I have a pretty big leaching field. There is no way to get from one side of my yard to the other, or to mow it without driving on it.
I hope it's deep!
Don't know how deep it is but it's been there for 25 years with no problems.
Mon Feb 24, 2014 6:03 pm
I sometimes drive over my leaching field without a second thought, but I do try to avoid going over the septic tank! But on the leaching field, if I broke through, I would not consider it a big deal - it's only a tile pipe surrounded by crushed rock. I would simply dig it up, put in a new tile, redistribute the rocks and call it quits. No way would I call the local Board of Health to come over to monitor or approve of my remedy, because they probably wouldn't - and then I would be in for $20,000 worth of septic system "improvements". I hate town "boards" and the "permits" they require for routine maintainance to ones properties. Al D
Mon Feb 24, 2014 6:17 pm
goldencub wrote:I sometimes drive over my leaching field without a second thought, but I do try to avoid going over the septic tank! But on the leaching field, if I broke through, I would not consider it a big deal - it's only a tile pipe surrounded by crushed rock. I would simply dig it up, put in a new tile, redistribute the rocks and call it quits. No way would I call the local Board of Health to come over to monitor or approve of my remedy, because they probably wouldn't - and then I would be in for $20,000 worth of septic system "improvements". I hate town "boards" and the "permits" they require for routine maintainance to ones properties. Al D
Mon Feb 24, 2014 10:42 pm
How are you going to know if you broke one tile ?
Tue Feb 25, 2014 10:04 am
It makes a sticky spot in the yard that gets stinky brown mud on your tire.
Tue Feb 25, 2014 10:23 am
It makes a sticky spot in the yard that gets stinky brown mud on your tire.
Or backs up into the tank and finally the house.
Tue Feb 25, 2014 11:45 am
danovercash wrote:How are you going to know if you broke one tile ?
Well, you're driving along over the leaching field and suddenly a wheel drops down into a depression that wasn't there 5 seconds earlier. You go and get a shovel and dig out the depression and, lo and behold, there will be a crushed tile. Remove it and set in a new one. Fill in the hole and you're all set (until it happens again, that is! ) Al D
Tue Feb 25, 2014 12:42 pm
When I was a kid we heated our house with coal. The dump truck would back in the driveway and put the shoot in the window and fill the coal ben. One day he backed to far back and ran over the tank. The driver was looking up at the sky. The whole back of the truck was in our septic tank.
Wed Feb 26, 2014 2:35 pm
Our drain field was put in around 2000, and it consisted of those big, black plastic, louvered inverted tubs that link together. They are pretty deep--probably 18" to the top. Almost the full length of a shovel from the surface to the bottom (don't ask). They are supposed to be able to withstand trucks driving over the top when properly installed. I wouldn't try it with the old drain tiles, though.
As far as the septic tank goes, I have wondered about that myself, but haven't had a chance to research the subject. Until I do, I would have to say to stay off it. A Cub would be bad enough, but driving a car or truck across it would be courting disaster in my opinion. Concrete itself is very strong in compression, but has almost no strength in tension. Where you have bending such as a beam or in the lid of the tank, you will have compression at the top and tension in the bottom. Structural concrete is reinforced with steel, to add tensile strength where it is needed. Non-structural concrete is reinforced minimally, with just enough steel to keep it from cracking too much as it shrinks while curing.
I'll try to call our local septic company when I get a chance, to verify if there is any kind of load rating on their tanks, or at least verify how they are constructed so I can run my own numbers on the lids. I'd do it now, but I am (supposed to be) working right now. I would expect, however, that these tanks are built only with enough reinforcement for shrinkage.
The main reason that my first reaction to this question is to stay away from the tank comes from the structural concrete code: ACI 318. It requires a certain thickness of concrete to protect the reinforcement from corrosion. This varies depending on environment. It can be as little as 3/4" of concrete cover where the surface is adjacent to an interior (protected, dry) environment, 1 1/2" to an exterior (periodically wet) environment, or 3" where the concrete is permanently cast against soil (permanently damp) or more for corrosive environments. For a septic tank, with soil on the exterior and a corrosive environment on the interior, that would require a minimum thickness of 6" plus the thickness of the steel itself. It's been a while since I had our septic tank open (and if you don't mind, I won't go verify this now, thank you very much), but I'm sure the lid was not more than 4" thick. Since I doubt they went to the expense to use epoxy-coated rebar or did anything else fancy to mitigate corrosion, I have to assume that the reinforcement will have a finite lifespan and will corrode within the concrete, thus leaving it eventually unreinforced.
What would be the lifespan? Good question. That entirely depends on the specific environment, and the construction of the tank. If the reinforcement was placed carelessly, and it is too close to the surface, its life will be shorter. Just as a typical guess, I could see it being as short as 10 years, and I wouldn't bet on anything longer than 25 years.
Does that mean that the lid will eventually cave in on it's own? Well, no, not necessarily. Concrete does have some strength in tension. Just not very much. Not enough to bother giving it any credit when designing structures. I would expect it to creep (sag), though.
Structural design has to be, by definition, conservative and examine the worst-case scenarios. Results in the real world therefore should come out better than the theoretical.
Off the top of my head, I would guess that a lightly loaded Cub would fall in between the theoretical and real-world: it would technically be heavier than what the lid capacity would calculate out to, but would probably be fine. With a full compliment of wheel weights and a loader full of dirt, however, I would stay off the tank. Certainly with a road-going vehicle of any kind, I would stay off the tank. With something really heavy, like a dump truck, I would stay at least 5'-10' feet away from the tank.
Just my two cents, without having run any real analysis or research on the subject yet. Maybe I am not giving the tank builders enough credit? Maybe they are designing these to be structural and carry a certain capacity? When I have a chance to do some verification on this, I'll post back. In the mean time, however, drive over your tank at your own risk!
Fri Feb 28, 2014 11:28 am
Thanks Tim, I'll be interested in hearing what you find out from the manufactures....and we also have the dome shaped "turtle back" drainfield.
Meanwhile, I bet THIS guy wouldn't hesitate to drive over it! http://www.youtube.com/watch?v=24vwfoJoLKU
Fri Feb 28, 2014 3:31 pm
Ok, here it is from an engineer's perspective.
If a septic system is installed properly, there should be no problem driving over it with a cub, or a truck for that matter.
The leach bed of a septic system would be the weakest point, since leaching tile is supposed to be installed within about 1-foot of the ground surface, to promote evaporation of the leachate (yes, leachate is supposed to evaporate, not disperse into the ground).
4-Inch corrugated drain tile, ADS, etc., standard acceptable load is 24-psi, and heavy duty is 30-psi.
Similarly, clay drain tile standard load is 66-psi, and heavy duty is 92 psi.
To put that in perspective, a standard Farmall Cub weighs about 1500 pounds. Front tires are 3" wide, so figure a 3" x 3" footprint on the ground per front tire, or 18 square inches in the front. Rear tires are roughly 8" wide, so figure an 8" x 8" footprint per rear tire, or 64 squre inches per rear tire, 128-square inches total in the rear. This gives your approximately 146 square inches of footprint on the ground at any given time. Divide the original 1500 pound tractor by 146 square inches and you get around 10-psi at any point on the ground.
As you can see, the Cub is at a minimum less than half of the minimum strength of any typical drain tile.
As for a septic tank, their strengths are even greater than the drain tile, and they are deeper in the ground, so really, there should be no issues at all with the tank itself.
This doesn't mean that it cannot happen, but, based on the manufacturer's information, a correctly installed septic system should not have a problem.
Looking at a truck, a typical pickup weighs about 6000 pounds. Figuring 4 tires at 10" x 10" on the ground, gives you about 400 square inches on the ground. This breaks down to about 15 psi, so again, you should not have problems even driving a pickup truck over a correctly installed septic system.
Fri Feb 28, 2014 4:21 pm
Been across mine with the IH 706 mowing with a Woods 3-pt. C-80 mower on the back and didnt fall in!---Didnt even know where the leach field was until I got the yard mowed off the first time.---I now mow over it all the time with the 185 equipped with the stupid FAT tires running 1 pound air pressure in them!---(they still beat my poor ole back a bunch). thanks; sonny
Fri Feb 28, 2014 5:32 pm
Amerigas insisted on knowing the location of the septic tank and drain field when delivering propane tanks, as did the backhoe operator digging out window wells, the tri-axle driver hauling a full load of stone and the guy with a honey pot from the cleanout service. I am postitive there are excellent reasons and horror stories to back up the need for each of them to ask. So I avoid it with my truck because it weighs about 5 times more than the Cub, I don't want a personal horror story. But I have been mowing over it with a Cub for 8 years and the previous owner mowed for 30 years with a Ford 8N.
Fri Feb 28, 2014 5:51 pm
Our septic system was installed in 1965. A tractor drove over it then and I drive my cub over it now. Had to have the tank pumped 3 or 4 years ago and the septic guy said everything is still in good shape. So, I still mow over it with my Cub. Since I use a Woods 59 I doubt if I get close enough to the center (there is a pipe coming out of the ground in the center...).
Fri Feb 28, 2014 10:11 pm
The company I work for manufacturers precast concrete septic tanks. It is not our main business...kind of a sideline. The old company here in the area that made them went out of business and we bought their stuff. Our main product and volume is in prestressed concrete box beams. Anyway...
Our tanks are designed per ASTM standards in residential lawns to withstand approximately 100 pounds per 10"x10" area, and 300 pounds live load in the same 10" square. West Virginia requires, as most other states that we deal with, a stamped PE reviewed shop drawing be submitted to the State and often county Health Departments...
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