Driving Piles Through an Old Timber Bulkhead

[NoWittyHandle]

I am involved in a forensic case, and I have a question about a possible fix. What happened was that a developer constructed buildings above an old timber bulkhead. The buildings overlap the back (land) side of the bulkhead by about two to three meters, with the buildings being constructed about two to three meters above the top of the bulkhead. The bulkhead is about twevle to thirteen meters wide at the top, with the sides sloped at an angle of about seven degrees. The timber bulkhead ranges in height from about seven to thirteen meters and rests on top of an organic silt layer that ranges in thickness from less than one meter to over thirteen meters thick. The bulkhead was contructed along a major river in the early 1900's.

The developer needed to raise the site grade to comply with flood regulations, and to do so he installed wick drains and surcharged. In one portion of the site, he did not install wick drains near the bulkhead because of the difficulty of installing wick drains through the timber bulkhead. The area without wicks varied, but many locations within fifteen meters or more of the edge of the bulkhead did not have wicks installed. The buildings are now settling and cracking, and our theory is that the combination of settlement and the lateral movement of the bulkhead is causing the problem.

One solution would be to demolish the existing buildings and drill piles through the bulkhead to support the reconstructed buildings, but I am wondering what this will do to the integrity of the bulkhead. It may not do anything to the bulkhead, but I wonder if anyone on the board has faced a similar situation. Possible solutions to this problem would be to drive the piles outside the timber bulkhead to cantilever the building (the buildings are three-story residential buildings) or to use lightweight fill, but I am looking for experience and/or opinions on driving piles through the bulkhead. Thank you for your responses.

 

[NoWittyHandle]

A word of clarification. I used the word bulkhead, but a timber crib might be a better description. Picture something made out of Lincoln Logs.

 

[msquared48]

Any possibility of using 2 to 3" diameter pin piles?

What is the condition of the crib logwork, or can you tell? Have any borings of the crib logs been taken?

Might also consider shotcreting the front of the bulkhead and installing tiebacks.

Thirteen meters seems awful high for a wood crib structure - 40 feet +.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[NoWittyHandle]

In response to your questions msquared:

- I don't know if pin piles will be big enough.
- The portion of the crib above the groundwater table was removed during construction. We have recovered some pieces from the upper part of the crib, and the wood appears to be in good shape.
- I don't think that shotcreting in front of crib and using tiebacks would be a viable alternative since the forces to be resisted by the tiebacks would be too big.
- We don't know the exact height of the crib, but I don't think that my estimate is off by much.