Passive soil pressure above a retaining wall rock socket

[shoup]

I am doing a redesign on a soldier pile retaining wall due to additional soil information encountered during construction. Rock was discovered between 7' to 16' below the front finished grade. I know that the wall needs to deflect to attain the passive soil condition. But at the rock there is no deflection. I am wondering if anyone has any ideas on how much passive soil pressure, if any, I can use above the rock.

The piles have already been delevered to the job site and if I use no passive soil pressure the piles are underdesigned. I am looking into using cover plates on the piles if I need to.

Thanks in advance for any help on this.

Scott

 

[DRC1]

In order to generate passive pressure the pile must deflect, although the required deflection for the passive pressire is less than that for active. The rock socket will prevent any deflection near the top of the socket as you basically have a fixed end condition. However, depending on your rock conditions and socketing details, you can develop some moment at the conection, which may drop your overall moment somewhat. Otherwise some other ideas would be to use a brace or anchors, unload a few feet at the top (be sure to go past the active zone, or if possible install piles on a slight batter to reduce lateral earth pressure - I know this works with driven piles but have never seen it with drilled in piles - talk to the driller.
Cover plates may be the simpest answer.

 

[shoup]

Thanks.

I will check into battering the pile, although I don't think it will provide enough resistance to prevent me from using cover plates. I have already taken out the possibility of tiebacks because the area behind the wall is a landfill. Otherwise, that would have been a more cost effective solution.

Scott

 

[cap4000]

Can you provide all the dimensions of the proposed temporary wall section with soil type and rock RQD data?? Perhaps a closer pile spacing is warranted, than the typical 8 feet c/c I normally use.

 

[shoup]

The pile spacings are just over 8 foot centers. However, they have already gotten precast pannels for the wall.

The RQD's are fairly low. They range from 0 to 68.

We have decided to increase the pile section to account for the increased moment due to the fixed pile at the rock. I then designed the rock socket assuming a course gravel instead of the rock. This should provide me with a conservative design both with the rock socket design and the pile design.

Scott