Drive equipment over septic drainfield?

[skipro3]

My system, a 4 line, Quick4 ISI Chambered leach field, has vents on the end of each line. They are 4 inch lines that poke about a foot above the ground and are capped but not glued. Supposed to be able to take the cap off to view down to the leach field I am told. I pulled one off tonight. Phew! Yup, that's a sewage leach field alright!!

 

[Richard]

Lemme see if this helps clear some things up...

I talked to the guys today and the septic guy says "flexible pipe" is very common here. He said it would be something like 10" in diamater.

He also said he felt after 10 years (maybe 9) that it's been installed that it "should" be ok to drive over.

Now...let's define drive over....

1. They need to get a backhoe in here to dig up lid on old tank
2. They need to get a gravel truck in here to fill old tank with gravel, then they're going to top it off with 4/6" of concrete on the top (of the inside)
3. Concrete truck needs to get in here to pour footers and pad for floor of room

I've taken a digitial picture that I'll try to post tomorrow at work to try to give some perspective

Unfortunately, I've got a (small) dogwood tree blocking one way in however, that same direction is also on a slope and they said the concrete truck couldn't come in that way with that degree of slope.

They want to take this tree out (that we've specifically built around trying to keep) and then take some 12x12 boards, scab some OSB onto them, maybe 8' long and build some "ramps" that they'll place on the ground to act as a "road", moving the ramps as the vehicle travels down it (build several sections and rotate them)

The septic guys says right now, we don't really know any answers until they "scratch around" some with his machine to find out where the pipes exit my house, where they enter the old tank and where they exit the old tank. Then, we'll know the elevations of what is where and how difficult this might be and where the equipment might need to be placed.

I am NOT too keen on the idea of a concrete truck traipsing through my front yard (although I'm not against redoing my front yard because it does need it) My issue is getting that kind of tonnage and knowing how they can cut through dirt/mud (if damp/wet) with their weight

I'll try to post that picture tomorrow morning

 

[Richard]

the contractor is afraid the old tank will settle if not filed with concrete for support

Exactly

Also, he called mine ...drats...what did he call it... a "rockless" or sandless? maybe a "no fill" system where the pipes were not surrounded by what is essentially, a gravel pit in the trenches.

They dug the trenches and put the flexible pipe in and as best I know, covered them up with dirt.

The guy who did it also dug my well and is well respected around here for doing good work (and nailed me a 100 plus GPM well!)

 

[Richard]

Actually, instead of the old tank settling, he's afraid that the weight of the addition on the ground, might cause the old tank to cave in and cause the foundation to settle.

(the new foundation will be within probably 3-5 feet of the old tank and it's supposed to be minimum of 10' if I recall)

 

[plowking]

Lemme see if this helps clear some things up...

I talked to the guys today and the septic guy says "flexible pipe" is very common here. He said it would be something like 10" in diamater.

He also said he felt after 10 years (maybe 9) that it's been installed that it "should" be ok to drive over.

Now...let's define drive over....

1. They need to get a backhoe in here to dig up lid on old tank
2. They need to get a gravel truck in here to fill old tank with gravel, then they're going to top it off with 4/6" of concrete on the top (of the inside)
3. Concrete truck needs to get in here to pour footers and pad for floor of room

I've taken a digitial picture that I'll try to post tomorrow at work to try to give some perspective

Unfortunately, I've got a (small) dogwood tree blocking one way in however, that same direction is also on a slope and they said the concrete truck couldn't come in that way with that degree of slope.

They want to take this tree out (that we've specifically built around trying to keep) and then take some 12x12 boards, scab some OSB onto them, maybe 8' long and build some "ramps" that they'll place on the ground to act as a "road", moving the ramps as the vehicle travels down it (build several sections and rotate them)

The septic guys says right now, we don't really know any answers until they "scratch around" some with his machine to find out where the pipes exit my house, where they enter the old tank and where they exit the old tank. Then, we'll know the elevations of what is where and how difficult this might be and where the equipment might need to be placed.

I am NOT too keen on the idea of a concrete truck traipsing through my front yard (although I'm not against redoing my front yard because it does need it) My issue is getting that kind of tonnage and knowing how they can cut through dirt/mud (if damp/wet) with their weight

I'll try to post that picture tomorrow morning

There are portable concrete pumping trucks with booms that can pump from the cement truck with hoses,it will add to cost but keep truck off the lawn. I also have a contractor who found a tank on a project after I had pumped all the existing tanks,this tank was under brand new lawn and landscaping.They called a company who brought a special pumper and filled tank by running hose and pumping some clay,paper combination off the truck to fill tank instead of caving it in. plowking

 

[CurlyDave]

Richard:

All of this stuff is heavy. And there is a way around most of it, for a price.

The gravel truck does not have to be fully loaded, but this will cost you more in transport fees.

Think about pumping concrete in. More expensive, but you can keep the concrete truck out of the area.

Another way to look at this is: what would a new leach field cost?

Actually, instead of the old tank settling, he's afraid that the weight of the addition on the ground, might cause the old tank to cave in and cause the foundation to settle.

How much would it cost to pour a grade beam that would prevent this problem by properly distributing the weight of the addition? I bet that would end up being less than backfilling the tank with concrete. Just fill it with gravel.

Many times, I have spent more money trying to save something than it would have cost to sacrifice the old one and get a new one.

 

[TedLaRue]

I just read through this entire thread, and I agree with many of the posts, but I think CurlyDave has a nice summary.

If the ground is dry, I wouldn't worry about a rubber tired hoe crossing the leach field once or twice, but a dumptruck full of gravel or a concrete truck is out of the question. Use the options CurlyDave suggests.

 

[Richard]

How much would it cost to pour a grade beam that would prevent this problem by properly distributing the weight of the addition?

What's a grade beam?

 

[Richard]

I think I forgot to add... they need to get the truck in here that will put in the NEW septic tank. This new location will be more towards the middle of the field (drain) than the end of the field as the current one is.

Again, I'll try to post some pics when I get to work (who me work at work? )

Also... (is this the beam?)

What if they brought in several truckloads of dirt (preferabley topsoil since I wanted to do that anyway)

Much like the egyptians perhaps, build a "ramp" to and over the drainfield so that the weight of vehicle will be an additional 12/24 inches ABOVE the current level of the grass??

Then, if they use topsoil, I can just box out the yard like I was planning on doing.

Is that a grade beam?

 

[MarkV]

I believe that Richard’s field is done with what we call “easy lay” here. It has perforated pipe that is surrounded with what looks like the Styrofoam pellets you use to pack fragile items and it is all held together with a wrap of soil fabric. The total package ends up about 10” round. This type of system has the advantage of not requiring gravel backfill and it does not have to be run in a perfectly straight line.

Richard the grade beam Dave is referring to does what a header over a window opening in a wood frame does. From the footing on either side of the the existing tank the concrete people would form a beam of concrete with a bunch of steel that would span the gap in the footing where the existing tank sits. It needs to be engineered but is a very common building practice. Often grade beams are used where native soil does not have the strength to support regular footings. In those situations they drive or pour pilings down to solid ground and then pour grade beams that sit on top of the piles for the building to be built on.

MarkV

 

[Richard]

I believe that Richard痴 field is done with what we call 兎asy lay here. It has perforated pipe that is surrounded with what looks like the Styrofoam pellets you use to pack fragile items and it is all held together with a wrap of soil fabric. The total package ends up about 10 round. This type of system has the advantage of not requiring gravel backfill and it does not have to be run in a perfectly straight line.

That description would blend nicely with the image in my memory (flexible ductwork that might be found in your home, other than being black)

I'm resizing pictures now, hopefully they'll help a bit?

 

[Richard]

Here's a side view. Builder said they couln't bring a top heavy concrete truck here with this angle (truck would be facing picture and would be leaning sideways)

Septic tank is on other side of tree and field is below tree, extending into the yard on far side

 

[Richard]

This is looking up

The red "X" is the approximate location of the current tank that they're going to fill in. The new tank will go to the left and will actually be a bit off the picture. Under (downhill) of the tanks is the drainfield.

Since the new tank will be to the left, you can see how the drainfield blocks the access. Also... the yard itself slopes down to a dropoff that is about 3' high so it's not easy bringing a truck up from the bottom. I don't think any of these pictures show the row of trees at the bottom of the yard

 

[Richard]

Looking down the hill, the house blocks some access, this dogwood blocks some access and then the drainfield blocks some access.

He told me yesterday he wants to take the dogwood down as that might give them better access.

We did everything we could to SAVE that tree so I'm not too keen on doing that, however, I did tell the wife last night that if he wants to replace the tree (his expense) then I'm ok with that

I might also offer to him that if he wants to replace the drainfield (with proper inspections when done) that he can rip it up all he wants. Again, this would be at HIS expense.

I was very clear about this situation prior to him quoting anything so if he's got some challanges now, he had ample warning and didn't do enough homework.

My feeling is, if I knew enough about this situation to 'warn' him upfront about these obsticles, (that he should be ahead of me on) then I don't really care what his challange is to get over them, nor his expense.

 

[Richard]

You can see here the dirt path where the elctrical has been routed around the drainfield. The electric is above the grass going to the left, almost out of the picture and then returns to the very near left. My transformer is right next to the tree who's leaves you see in the picture. Both (among others) are yet more items in the way of easily moving equipment around on my yard

 

[CurlyDave]

Richard:

MarkV very nicely describes what a grade beam is.

One reason I suggest it is that I have a hard time understanding how filling a septic tank with gravel and then pouring concrete on top of it is going to help with potential settling. If the gravel settles, the concrete on top of it will settle also. The concrete will not be reinforced, will be impossible to inspect during or after the pour, and will not be particularly strong. I think the concrete would crack into pieces which would settle with the gravel.

A grade beam is a poured-in-place reinforced concrete beam. The steel reinforcement can be easily inspected before the pour, it is supported by earth on both sides of the tank. A common construction technique with the advantages of being inspected and reliable.

In order to properly abandon the old tank, it must be filled to prevent anyone from falling into it, but there is no reason at all to use it as a support for your foundation.

Another possibility here is to think about mapping out a route for heavy equipment that goes over the end of your leach field furthest from the tank. If there is any damage that would produce the least damage.

- - -

Just a piece of advice. You need to be careful about your relationship with your contractor. If he decides he can't ever make any money on this job, he could just walk away. You could lose whatever you have paid him so far. Especially if the contract doesn't spell out some things, like the dogwood tree. I know you told him about this stuff, far in advance, but if his interpretation was "it is OK to drive on the septic field" and yours is "it isn't", unless your contract says it isn't OK, it is not a clear cut win for you if there is a dispute.

 

[Richard]

I fear I've been a bit vague...?

The foundation will not be OVER my old septic tank at all.... the fear is the weight of the foundation might cause lateral pressure on the side of the (hollow) tank and allow the tank to cave inwards if it wasn't filled first. Then allow the foundation to settle.

That's why they want to fill it rather than remove it... they tell me if they remove it (other than I suppose it being gross) they will then not have packed soil in that location. If they simply fill the tank with gravel and "entomb" the gravel with a 4 or 6 inch layer of concrete on the top then that mass should (would?) be strong enough to prevent the sidewalls from ever caving in.

The tank is currently maybe 20' from the edge of the house, after we add the room, the edge of the house will probably be within 3/5 feet of the current (and soon to be old) tank but NOT on top of it.

Does that change any logic?

 

[horse7]

The equipment for the foundation (digging, concrete, backfill) is only the beginning. If those vehicles can't get in, what about the trucks for the rest of the building? They may have a higher ground pressure than a TLB (narrower tires for instance).

The existing structure looks multistory, so probably the addition is, usually (if you are sane) you want a boom truck or crane to get stuff onto the 2nd floor and roof but those need access... if you had access, you would not have a problem now. So it looks like whatever solution chosen ought to also apply to everything else that will be needed.
.

 

[Red55]

I fear I've been a bit vague...?

The tank is currently maybe 20' from the edge of the house, after we add the room, the edge of the house will probably be within 3/5 feet of the current (and soon to be old) tank but NOT on top of it.

Does that change any logic?

I'm NOT an engineer but the way your contractor is handling is O. K. the problem would be if you disturbed the soil or didn't fill the tank. Just a word of caution Curly Dave is right about your contractor. He's in the business and he will find ways to recover monery losses on your addition. It is much better to work with him that trying to put the screws to him for his own mistakes It's usually cheaper too! I always run into people who are looking to do it the cheapest way possible and I tell them that it is ALWAYS cheaper to do it right that to do it over. Had a customer that wanted me to use cheaper roofing materials to match a lower estimate ($350) and I asked her when the roof leaks will she blame me or the cheaper materials? She laughed and I ended up giving the job to my BIL -Ed

 

[CurlyDave]

If it were my job, I would use the grade beam, but there is a good chance that gravel fill plus concrete cap will be OK if the addition stays 3-5' away from the tank. Of course, if it were my job, I wouldn't be hiring a contractor, I would do it myself. My philosophy has always been that I would rather spend $500 on extra concrete and steel than spend $500 on engineering to prove I didn't need the concrete and steel.

There is a another area of non-compacted earth you should be aware of, and that is the backfill around the existing tank.

When the tank was installed, they dug a hole which was bigger than the tank, probably ~12" clearance on all sides, put the tank in, and then backfilled. It is almost impossible to compact that backfill, and in most situations it doesn't really matter. Over the years, it settles some, but it is never, ever, going to reach full compaction. Put a force on that soil in a new way, and it will settle some more.

The problem with building on unstable soils, and this soil is unstable, even if the rest of the property is stable, is that settlement issues frequently don't show up for years. In most states, a contractor is liable for his work for one year. By the time settlement shows up, he is no longer liable, if you can even find him. In fact, a lot of contractors build something, see that it is OK for a few months, and then go away thinking they have built something which was just fine.