Embankment Construction Over Soft Soils/Swamps

[BigH]

I remember when we were in University, the geoprof indicated that when building embankments over very soft clays and swamps, one should build the outer edges first, then infill the center. I was perusing Ontario's OPSS 209 for embankments over swamps and found the same thing. Does anyone know the reason for this? The link for the OPSS 209 follows - see Clause 209.07.04.02.

http://www.raqsb.mto.gov.on.ca/tech...8ecf852568070071342c/$FILE/OPSS 209 Mar98.pdf

 

[emmgjld]

If you start on a side and start building across, you start 'pushing' the muck ahead of the fill. More fill material is required and the fill is not as solid. I have understood it to create a small slope failure at the leading edge of the fill, which gets incorporated into the lower fill/upper subgrade.

 

[fattdad]

wouldn't surprise me if it's not about time. Getting the toe stable initially will help in the long run.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

emmgjld - I've done the "rolling surcharge" displacement method before - had a huge mud wave in Bauxite tailings where I displaced 39ft of them with causing failures in fill edge. But the method says you do both edges and then infill the middle - something tells me it is not about displacement as both edge would trap displaced materials in the middle. Thanks for the comment!

 

[emmgjld]

I was meaning that the mud wave is what is to be avoided by doing the edges first. My experience is that careful working from the edges, allowing the fill & subgrade materials to 'set' a bit results in significantly less stressful (for the owner & contractor) fill placement. I wish I had used the procedure in the deep lakebeds of the Crested Butte Ski Area in '75. I would have been a real hero!!!

I have tried to make the fills several ways on both small excavations (utilities road fills and small residential) & larger commercial. I admit your Bauxite Tailings sounds like something to be envious of.

 

[BigHarvey]

You can build an embankment by creating a failure and pushing a wave of soft material which will be replaced by good material. It's a controlled failure and must be done by an experienced earthmoving contractor ( to my knwledge, it's a technique used only in North America ).

If you have a more competent layer within 5 to 6 meters of depth you can also use dynamic replacement ( maybe associated with vertical drains to have an immediate relief of porewater pressure ).We have built a 12 m high iron ore fill over 7 m of poor hydraulic fill ( qc = 0, Wn close to 90% and 90% below 2 microns )after substituting the top 2 m with good sand to have a working platform. measured settlements after treatment were less than 20 cm.

The polish use also explosives for embankment construction in soft soils including peat.

 

[emmgjld]

Explosives!! I have had a couple of contractors & owners for which this could have been appropriate.

 

[BigH]

BigHarvey - I've used the Rolling Surcharge method as mentioned before in displacing 39 ft (13 m) of tailing slimes at a Guyanese Bauxite mine - that was back in 1978. As for explosives, we have used them on the Rainy Lake Causeway - I'll find the papers and post them here later - it is pretty remarkable - by my geotechnical mentor. That's impressive on the dynamic compaction.

I'm aware of these other methods and have used them, I just wanted to know what the rationale was behind placing embankments from the outside in . . .

 

[BigHarvey]

The only advantage I see beginning with the edges is that when you start infilling the center, you will have prestressed the sides and therefore will be less likely to trigger a slope failure.
We did for such a problem some dynamic replacement where the stone pillars were limited to 3 rows on each side and nothing in the center, just to reinforce the ground where possible slip circles could appear.

 

[emmgjld]

I realized that I hadn't addressed the main question BigH asked. After our informative rambling BigHarvey came up with a shorter answer than I was formulating. Good for you!!

 

[BigH]

BigHarvey is probably correct - - good answer!

 

[dgillette]

One more reason might be push distance. If the fill is too soft for trucks or scrapers so it all has to be pushed with tracked equipment, the distance to the leading edge from solid ground is shorter if you can work from all sides (and you can have more equipment working at a time if you approach it from more directions).

Also, if you push all of the stuff to one side instead of trying to trap it in the middle, you have to deal with it where it pushes up onto the far shore (which could be a big deal if your bauxite tailings are the red mud variety w/ pH>12).

Big H - I finished up here in Bogor at noon today (Friday), then it's back to the States late Saturday night. Nice people and I had a great time, but preparing and delivering 20+ hours of lecture is a lot of *(^% work (although probably very useful for them). I think I've had my picture taken more in the last 9 days than in the previous 53 years. Waiting out the rain in the Salak, hoping it will clear in time so I can spend another evening wandering around aimlessly, trying to identify which streets are interesting, and which are TOO interesting. Went to a tea plantation up in the hills last night, and now I need to go shop for Java java, or Sumatra java. One of the participants got me some Papua java.