Sheet pile be restricted on rock?

[Scottie25]

My anchored sheet pile design requires a sheet pile depth of 6m in foundation soil however there is bedrock located from 3m below foundation soil in some places. Is there a method available to hammer or secure the sheet pile to the bedrock without damage to the sheet pile? The bedrock is quite weathered and fractured.

 

[PEinc]

No way to guarantee no damage. When the rock gets hard, the sheet stops. If you keep hammering, you probably will damage the sheet.

http://www.PeirceEngineering.com

 

[PEinc]

Could you more clearly explain where the rock is with respect to the excavation subgrade?is rock above subgrade?

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[eea]

I agree with PEinc. I would consider revising the design for a reduced embedment of 3m rather than the current 6m (possibly using a lower tier anchor). Any "toe'ing" into the rock should be some benefit to the wall but not one I'd count on from a structural design.

 

[Ron]

Agree with above comments. There is also a relationship between RQD and damage to the pile...I just don't remember it exactly. My thought would be if RQD is less than 50... Probably ok

 

[PEinc]

If hard rock is horizontally fractured in layers of 4 inches or less, the RQD would be 0 and I would not expect to be able to drive sheet piling into the rock. In a core sample run, the RQD could be relatively low but there could still be a hard, impenetrable zone through which a sheet pile could not be driven. Once blow counts get high (maybe 50 bpf), sheeting becomes difficult. Once blows rise to 100/few inches, this is refusal and I would not count on sheet pile penetration.

http://www.PeirceEngineering.com

 

[BigHarvey]

If you really need that kind of embedment in rock, use a combi-wall (pipe plus sheetpiles in between). The steel pipes are installed using a drilling method ( DTH generally)down where required and the sheetpiles stopped on the bedrock.

 

[RFreund]

BigHarvey - Just out of curiosity what size diameter are these pipes typically or some sort of min/max?

EIT

http://www.HowToEngineer.com

 

[PEinc]

You can find details for combi-walls on the web sites for Skyline Steel and L.B. Foster. Sometime the walls use pipe piles, sometimes wide flanges, or even H-Piles.

http://www.PeirceEngineering.com

 

[BigHarvey]

It all depends on efforts, hence retained height. For some quay walls it can be as high as 1.5m diameter, rarely under 600mm. You must be sure to work with experienced contractors, non vertical piles can lead the sheetpiles to declutch. Prefer 3 sheetpiles between the piles to allow some flexibility. Steel tubes can also be replaced by caissons made of sheet piles (but you can experience problems associated with welds failing during driving )

 

[BigHarvey]

In your specific case, in order to allow OD drilling methods, you shouldn't go over 1 m diameter.

 

[RFreund]

Interesting, thanks guys.

EIT

http://www.HowToEngineer.com