# Storm sewer in poor soils?



## HUI (Jan 21, 2011)

I have a county project that involves laying 24" RCP. Total footage of about 7000'. I have about 75% complete and now we ran into bad soils. The invert of the pipe is about 6' deep. The soils engineer bored the ground and the results are the top 5' are muck, then there is a couple of feet of peat and then the rest is marl down to about 15'. Then water sand. I was directed by the engineer to over excavate and fill with #8 crushed rock ( about 3/4"). So we did as directed and the pipe is still settling. The soils engineer is now calling for 24" of #2 crushed rock then the #8 above that. I think what is happening is the column is too narrow to support the pipe. Last I checked we were 7' wide and about 10' deep with stone. I also think the stone is absorbed horizontally by the marl walls. Which the creates a void for the pipe to settle. 

Anyone run into this much bad ground? Our ideas so far are to increase the bottom area of the rock and build it In more of a bell shape. We are also considering going from RCP to say Hancore HP or ductile iron. Just looking for any ideas. 

Thanks.


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## jhark123 (Aug 26, 2008)

I think that is the DEFINITION of a nightmare.

Have you considered a geotextile below the stone?


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## HUI (Jan 21, 2011)

I have. The problem is ground water. And the sloughing of the sides. As you dig the I'm this crap the walls just ooze in and squeeze the buckets and trench box. Then because there isn't not a bottom the excavator has no footing to pull a trench box or a bucket full of this crap


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## Cuda (Mar 16, 2009)

Soils stabilization with polyurethane foam grout injection.


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## HUI (Jan 21, 2011)

Never heard of the grout injection. Do you have any contacts or websites?


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## Crocop (Nov 29, 2011)

Look up a company called uretek they do urethane foam grouting


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## PipeGuy (Oct 8, 2004)

HUI said:


> ...we ran into bad soils. The invert of the pipe is about 6' deep....top 5' are muck, then there is a couple of feet of peat and then the rest is marl down to about 15'. Then water sand. I was directed by the engineer to over excavate and fill with #8 crushed rock ( about 3/4"). So we did as directed and the pipe is still settling. The soils engineer is now calling for 24" of #2 crushed rock then the #8 above that. Last I checked we were 7' wide and about 10' deep with stone. We are also considering going from RCP to say Hancore HP or ductile iron. The problem is ground water. *And the sloughing of the sides*. As you dig the I'm this crap the walls just ooze in and squeeze the buckets and trench box. Then because there isn't not a bottom


Dewater, dewater, dewater. The soil oozes because its being "pushed" by water. Until you remove the water from the equation you're fighting an uphill battle; potentially straight uphill. And if the soil is deflecting the sides of the trench shield to the point it confines the free movement of the bucket than its under-rated for the soils conditions. If it were me, I'd be wanting an approved change order before I went any further. I can't imagine the scope of work you're describing is within that of the County's contract; wether or not unit price line items are provided. The ground conditions you describe can easily make the last 1000 feet cost more than the first 6000. Good luck.


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## griz (Nov 26, 2009)

Perhaps the water table & soil conditions will not be alleviated by de-watering.

I agree with the C/O, but it sounds as if you are at the mercy of an Engineer. It's his problem to fix & yours to implement....

Does your contract/job specs cover this issue? to what remedy?

Good luck...:thumbsup:


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## HUI (Jan 21, 2011)

No there were not soil borings done in this area. These issues are above and beyond of the original contract.


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## S.R.E. (Apr 8, 2010)

Are you digging inside the trench box? I agree with the dewater stuff said above. I can't believe he had you using 3/4" rock. I would think you would need a base of at least 8"-12" rip rap that is at least 2' deep and then you place 6" of pipe bedding on top of that. Also make sure that your box is not below the pipe when you drag it. I would want the box to be at least above the spring line of the pipe when you drag it. Around here they usually refer you to the state spec for this and I know it does not call for 3/4" rock.

Have you considered using sheet pile and frames ? A company I worked for a while back would use that type of shoring when we had wet nasty ground. We would dig down about 4' then set a frame. Then we would set the sheet pile and just lap it. Then we would drive the sheets down and dig inside the frame. As the frame would settle down we would add frames as needed and hold them up with chains. It was a slow process and we would get about 3 sticks of pipe a day depending on utilities in the area.


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## griz (Nov 26, 2009)

Helical piles with support cradles for the pipe?...


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## HUI (Jan 21, 2011)

I think helicles or wood piles with a cap. I have a meeting with the engineer and the owner tomorrow.


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## PipeGuy (Oct 8, 2004)

HUI said:


> I think helicles or wood piles with a cap. I have a meeting with the engineer and the owner tomorrow.


That's friggin' crazy. Piles and pile caps for a 6' deep storm sewer?

If you can get a workable excavation to 2' - 3' below pipe subgrade there's hardly any ground condition that a combination of geotextile, 4" stone and 2" stone won't make suitable to lay a 6' deep RCP storm sewer on. Use a woven fabric to keep the stone segrated from the surrounding soils and extend the stone section from 2 or 3 feet below the pipe to a foot abve - again wrapping the whole section in fabric. It might even help to have a layer of geogrid in there somewhere beneath the pipe.

Just out of curiosity, is the grade really flat? Is this a single long rrun carrying flow over a distance or a "trunk" with "branches".


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## HUI (Jan 21, 2011)

Yes the grade is flat. We are laying the pipe in a bean field in northern Indiana. 

I would agree with you on the stone and fabric. And it seems that some combination would work. The problem though that with using RCP it does take much settlement to open up the joints. 

With these soils they are organic so they will continue to decay. Over time the entire pipe will settle thus opening up the joints. 

We are digging with a 336 Cat. When you are excavating you will take a bucket swing and dump then come back around to get another bucket, the bucket will not fit in the trench because the walls are sloughing. 

You can also taken the bucket and just push it into the ground just about as far as you want. There is very little resistance.

By far the worst soil conditions I've ever seen


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## S.R.E. (Apr 8, 2010)

HUI said:


> We are digging with a 336 Cat. When you are excavating you will take a bucket swing and dump then come back around to get another bucket, the bucket will not fit in the trench because the walls are sloughing.
> 
> You can also taken the bucket and just push it into the ground just about as far as you want. There is very little resistance.
> 
> By far the worst soil conditions I've ever seen


You need to dewater and use trench boxes. Dig inside the trench box, keep pushing box down to bottom of base. Place and compact base inside box, Pull box up, place bedding, pull box up, lay pipe, bed pipe, pull box up, place about 2' of backfill on top of pipe before removing box. You will most likely have to use two trench box setups and have both in the ground most of the time. You will need to leave one in at all times so the bell is in the middle of the box. Good luck!


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## S.R.E. (Apr 8, 2010)

HUI said:


> I would agree with you on the stone and fabric. And it seems that some combination would work. The problem though that with using RCP it does take much settlement to open up the joints.
> 
> With these soils they are organic so they will continue to decay. Over time the entire pipe will settle thus opening up the joints.


Not cheap but, you could use ductile iron pipe with field lock gaskets. they will not pull apart.


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## HUI (Jan 21, 2011)

Thought that as well.but once you get the box in there isn't solid enough material under the excavator to pull the box even with 20' wide mats below the excavator


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## S.R.E. (Apr 8, 2010)

Maybe you should just bore through the nasty area. Of course it would probably sink....


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## HUI (Jan 21, 2011)

Yeah we have a 36" auger bore to do in about 500'.


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## rino1494 (Jan 31, 2006)

They run pipelines through wetlands and swamps all the time. My buddy was on a pipeline job where they could take the bucket off a John Deere 270 and push it all the way into the swamp up to the boom. They welded the pipe together and floated it into the swamp.

Look into a well point system, over excavate poor soils, place geo-tex, backfill with some #4 stone, place some gravel for bedding and fuse HDPE together and possibly concrete it.

Either way, this is going to cost the county a crap load of money.


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## PipeGuy (Oct 8, 2004)

HUI said:


> Yeah we have a 36" auger bore to do in about 500'.


Anyone looked at a directional drilling option? It might take a lot of fluids to support but I'd think it could be done. Fusion bonded HDPE would eliminate the joint seperation issue and be a lot cheaper than steel casing.


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