Septic Tank Driveway

[Pirate]

Bought this house about 3 years ago. It was built in 1993. The tank is 8 feet from the back of the house, directly under the gravel drive for the basement garage. The other side of the tank is the gravel driveway to the front of the house.

I'm becoming worried about cracking this tank. Right now my son parks his small car in the basement garage. Last time I had it pumped out I put a 1/2 steel plate over the access hole since the cement cover was broken (another stupid move on my part, I should have used aluminum). I recently told him to stop parking in that garage and to not park over the tank.

I'm wonder is there is a way to pour a "bridge" or something over that tank so we can drive cars over it. I'm a bit pissed off the county allowed him to put the tank where they did. I was septic stupid when I bought the house so it didn't click in my giant brain that I may have a problem. Moving this tank would be a major undertaking as I live in the woods and don't want any trees cut down. I won't even bring up my drain field location.

I did some internet reading and only found one idea - put a riser on the tank access and then pave over area with thick concrete slab. I think that might work but I can't get past the riser idea. If a vehicle tire is directly on the riser, I think all of the weight is transferred directly to the top of the tank, thus I wouldn't put a riser on even though last 2 septic pumpers recommended it. Tank is about 2.5 feet deep, I don't mind digging the dirt/gravel off the lid.

 

[Oldtrout]

OK...Now how can we help??

 

[LBrown59]

Bought this house about 3 years ago. It was built in 1993. The tank is 8 feet from the back of the house, directly under the gravel drive for the basement garage. The other side of the tank is the gravel driveway to the front of the house.

I'm becoming worried about cracking this tank. Right now my son parks his small car in the basement garage. Last time I had it pumped out I put a 1/2 steel plate over the access hole since the cement cover was broken (another stupid move on my part, I should have used aluminum). I recently told him to stop parking in that garage and to not park over the tank.

I'm wonder is there is a way to pour a "bridge" or something over that tank so we can drive cars over it. I'm a bit pissed off the county allowed him to put the tank where they did. I was septic stupid when I bought the house so it didn't click in my giant brain that I may have a problem. Moving this tank would be a major undertaking as I live in the woods and don't want any trees cut down. I won't even bring up my drain field location.

I did some internet reading and only found one idea - put a riser on the tank access and then pave over area with thick concrete slab. I think that might work but I can't get past the riser idea. If a vehicle tire is directly on the riser, I think all of the weight is transferred directly to the top of the tank, thus I wouldn't put a riser on even though last 2 septic pumpers recommended it. Tank is about 2.5 feet deep, I don't mind digging the dirt/gravel off the lid.

It's not a good idea to drive over or park on the tank. as it could cave in from the weight.

 

[Pirate]

It's not a good idea to drive over or park on the tank. as it could cave in from the weight.

I know this. I'm looking for a solution to keep using the garage drive other than moving the tank.

 

[Tig]

Be careful with the riser idea, it could have the opposite effect of what you want to do. As you described it will focus the weight on the tank. Right now you have 2.5 feet of earth distributing the weight.
Something like curbstones upside down and flush with the ground would distribute the weight even further. You can remove them to access the tank. You could even hide them under 4" of gravel.
How wide it the tank? 2.5 feet deep is quite deep. Possible deep enough that there is no issue for a car.
What is the tank made of?
Just my $.02 CDN

 

[CurlyDave]

I am afraid that the safest thing to do is put a white picket fence around the tank.

I suppose you could dig footings on opposite sides of the tank for footings, and then build a bridge of sorts over it. The problem I can see is that one false move with a backhoe will crack the tank. I am not even certain that you could dig around that tank without creating a problem. The pressure of the earth on the sides probably counteracts the pressure from the liquid inside.

I would avoid a thick concrete slab over the tank. It will probably weight more than a car, and could crack your tank, especially while it is being poured when it has all the mass, but none of its final strength. While I can think of worse situations, the concept of several tons of wet concrete mixing with a thousand or more gallons of sewage, all right in my backyard gives me the willies.

The most cost-effective solution I can think of is a new carport or even a garage, somewhere else.

Explain the consequence of a collapse, with his car falling into the contents of the tank, to your son...

 

[Tig]

My tank is about 3' by 6' and made of concrete. I would not like it in my driveway but if it were there and 2.5' deep I would probably do the curbstone bridge.

 

[JB4310]

I'm no septic tank expert though I have 3 on my property, one of mine is about 2 feet below my back gravel driveway to my shop.
I never gave it any thought till reading your thread, but I honestly don't think you have anything to worry about with light vehicle traffic, I'm driving a 12,000 pound truck over mine. Mine's concrete reinforced with steel, it's already built like a bridge. Yours being 2.5 ft deep is added protection, might be more worried if it was very shallow.

Just have to warn equipment operators of the tanks location, I've heard of guys with tree bucket trucks finding them the hard way when all the weight is on an out-rigger on top of a tank.

If your not going to sleep well worrying about this though, I have a solution. Dig down about half way and lay a heavy plate of steel down, something like what they use to cover trenches in the road, 3/4-1" thick and 4'x8' wont be cheap but that would spread the weight, bridging the tank like you said to the surrounding area around the tank. you would need a hole in the plate for access which you could cover with steel also, Don't know why you would need aluminum, if your worried it will corrode? not in your lifetime. Cover it back over with the gravel you dug out.

You could do it cheaper substituting wood for the steel, screw 2 pcs of 3/4" PT or marine plywood together, could stiffen it up more by framing the wood platform with 2x4-6.

I know, wood in the ground, doesn't sound that great but I would think it would last many, many years.

If you did the riser and concrete slab, just don't bring the riser into the slab, have it just below the slab and have a recessed steel access cover in the slab, this way driving on the cover would not push on the tank. I personally think that's a little over kill going that whole route but it would make it easier to service the tank if needed..

Good Luck, JB.

 

[LBrown59]

Be careful with the riser idea, it could have the opposite effect of what you want to do. As you described it will focus the weight on the tank. Right now you have 2.5 feet of earth distributing the weight.
Something like curbstones upside down and flush with the ground would distribute the weight even further. You can remove them to access the tank. You could even hide them under 4" of gravel.
How wide is the tank? 2.5 feet deep is quite deep. 1*Possible deep enough that there is no issue for a car.
What is the tank made of?
Just my $.02 CDN

1* I wouldn't want to bet on that.
A few years ago a distant neighbor crashed his riding mower through his concrete tank while driving over it.

 

[LBrown59]

Explain the consequence of a collapse, with his car falling into the contents of the tank, to your son...

A neighbor of mine had to do just that only it wasn't his car it was his riding lawn mower.

 

[MikeD74T]

Planking over a septic tank that down 2 1/2' is no different than crossing soft ground. Dig in doubled 2x12x8' PT in the tire tracks & drive over them. You're not talking concrete trucks here. The planks will never see more than 1/2 the cars weight. 2500 lbs ( a full sized pickup) distributed over 16 square feet won't damage your tank. I have put 10 wheelers of crushed stone over triple plywood on a lawn with no visable damage.

A lot of the "fell thru the tank" stories come from the old steel tanks. The cover was like a drum & would rust thru. I know a lady that was launched off the toilet when her husband drove a loaded dump truck over their steel tank. The bending cover worked like a giant plunger, in reverse. She made him clean the bathroom. MikeD74T

 

[DanD78]

I think if you would do the math and pour a 4" slab over the entire area you would find that the concrete weighs less per square foot than your car and if you do drive over it the weight will be spread over the area of the slab not concentrated in the tire foot print.

As far as the access hole use a 20" plastic pipe as a sleeve between the top of the tank and the bottom of the slab but so no weight gets transfered to the tank. Make a steel lid to fill the hole in the drive slab.

You might want to ask an engineer instead of a bunch of guys that think they know best, my self included.

Dan

 

[MrWoodChips]

While I can think of worse situations, the concept of several tons of wet concrete mixing with a thousand or more gallons of sewage, all right in my backyard gives me the willies.

This does suggest one good idea. ANYTHING you do is best done only after you have the tank pumped.

John

 

[Pirate]

You might want to ask an engineer instead of a bunch of guys that think they know best, my self included.

Dan

Ya know, I didn't even think of that. I had an engineer out once when I had a sagging floor. Structural guy. I'll have to call him about this too. Not sure if he can provide any advice though unless I remove all the cover and totally expose the tank top. I'm not looking forward to that since I just pumped it.

 

[JoeL4330]

If you are willing to put a slab in, then the riser doesn't need to bear any weight at all ...think manhole cover...the riser can "slip by" the slab ...a little extra rebar in the slab to hold the "manhole cover". Of course, I'm no engineer

 

[Eagleview]

A reinforced slab over the tank would work , but if the tank or fittings fail at any time it will be a major ordeal to replace it or fix the fittings . I would fill it in with good road base gravel and put a new tank and absorbtion trench in a more suitable location . It would be no more expensive than the concrete slab and is a brand new system .

 

[tommu56]

Think of a man hole in the street you drive over them all the time there at wiring vaults under there too that I've seen some a good 8'W 12'L and 8'deep

I would call a precast company explain what you what you have and ask them for recomendation they might even tell you what the load design for them is.

or get them to make a precast piece to sit on the edges of the tank no load in the center were the cover is. make some sort of slip joint to on tank outside sitting on new bridge/cover with a manhole rings laid up to grade on the bridge with a manhole cover at grade.

tom

 

[Pirate]

Lots of great ideas. I really can't move the tank. I'm on top of a small ridge. No yard to speak of. Front yard is only 20 feet from porch to woods/steep slope down. Back of house is driveway then steep slope down. You get the idea. If I were to move tank, I would have to move entire system because I would end up putting the tank where the drain field is now and then run a line down a hill to a small holler where I think I could put the drain field. Lots of "I thinks" in this mess. It would be cheaper at this point to cap the tank with nice thick slab and stick a riser in. I like the idea of having a manhole cover supported by the slab and not on the riser. You can see the lower garage in this http://s215.photobucket.com/albums/cc53/pirateghostabc/3 May 2008/?action=view&current=IMG_0013.jpg You can look at other pictures if you are bored while you are there.

 

[guyrj33]

When our system was installed we had a heavy duty cover put on, it's strong enough to drive a truck over. Perhaps you can replace the cover on your tank. An engineer might be able to look at your cover and tell you how much weight it can carry.

 

[Pirate]

When our system was installed we had a heavy duty cover put on, it's strong enough to drive a truck over. Perhaps you can replace the cover on your tank. An engineer might be able to look at your cover and tell you how much weight it can carry.

I'm worried about the tank itself. I already replaced the "cover" with 1/2 steel plate. I believe you are talking about the small access cover usually only a couple of feet across, right?