Anchoring a Caisson Pile Reservior wall in unconsolidated soil

[jwilson1]

I'm a civil engineering intern and haven't even gotten through geotech yet.

My supervisor is investigating the necessary methods for anchoring a thirty foot caisson pile wall into unconsolidated soil. It's for a gravel pit reservior in the Rocky Mountains, that was backfilled.

It will be tied back from top to bottom as the backfill is removed, but the water table in the area is very high. The final product is hopefully a watertight storage reservior.

The caissons will go down from the toe of a tenfoot high 3:1 slope. Thirty feet to bedrock and into the bedrock about five feet.

 

[jwilson1]

So my question is: what sort of anchoring can I use?

 

[PEinc]

Your question is too general. The type of anchor depends on (1) the type of soil or rock into which the anchors will be bonded, (2) the drilling conditions, (3) the grouting method, (4) the preference of the anchor contractor, (5) the anchor design load. Most likely, the anchors will be drilled and grouted threadbars or multiple 0.6" diameter strands. You will need the tendons to be corrosion protected, probably with corrugated encapsulation. You may be installing rock anchors rather than soil anchors.

You should discuss this with your supervisor after you review ground anchor information in text books and/or in some of the FHWA's ground anchor manuals, some of which are available on-line at the FHWA Geotechnical Publications web site.

 

[jwilson1]

Thanks for the input, I'll try to narrow it down a bit.

Alrighty

1) The type of soil I'm working with was not made explicit, I know it is a wetland area and most likely unconsolidated; I don't anticipate having rocks to bind my anchors to.

2) Most of my drilling will probably be below the water table, using something to stop water from escaping, maybe 'drill mud'?

3)Grouting between the caissons or into the holes made for the anchors? Is this a binding agent?

4)My supervisor isn't expecting much, since we are working off of a very preliminary engineering report for the site, so I'll try to contact contractors in this expertise.

5)Design loads go beyond what I am investigating. I understand thier huge impact on the anchor selection but is is there a specific type of anchor system that can deal with the material I am trying to work in.

Ultimately I have to work with the soil in the area, unelss I angle into bedrock. I dont think I can tamper with the the wetlands in any way.

I'm pursuing the FHWA codes, now and am sure I'll have more questions about them as I go on. Do these codes apply when considering a reservior wall though? There must be some other considerations that must be taken into account.

 

[PEinc]

1. If you do not know what type of soils you have and how dense of loose they may be, you can't design tieback anchors. You can't even be sure tiebacks will work , especially if the soil is very loose or soft.

2. Anchors can be drilled through a wall with water behind the wall. They have done this at the World Trade Center and other jobs. However, it requires special, sealed openings to be installed into the wall before drilling all the way through the wall. The seal contacts the OD of the casing pipe to prevent water and soil from coming through the wall.

3. Grouting can be done to seal leaks. Talk to a contractor who has done secant pile walls that needed to act as cut-off walls also.

4. Talking to contractors is a very good idea. Make sure the contractors have much experience in similar jobs.

5. See 1. above.

If rock is relatively close, you could use rock anchors. The longer they are, the more expensive. Rock anchors can also have higher design loads, therefore allowing less but more expensive anchors.

FHWA's permanent anchor design recommendations are not written specifically for non-highway projects. However, even though often conservative, the manuals have a lot of good information which many people use for non-highway projects.

 

[jwilson1]

Thankyou, I've certainly learned alot from reading through some of the FHWA on-line resources.

It seems that I need some boring reports before I can even get an idea of the necessary methods and types of anchors I should be using.

4) I'll see what I can find with contractors in my area.

Thanks again.

 

[PEinc]

Contact Schnabel Foundation Company's office in Colorado.

http://www.schnabel.com