Reuse of Existing Piled Foundations 2

[pjheaphy2]

I am currently researching the possibility of reusing existing piles. Its coming along nicely but im finding it very difficult to come across good information on using new piles and existing piles together. My biggest factor is combating differential settlement. I propose using a form of shear wall between the piles to combat the settlement. I was wondering does anybody have any relevant papers or helpful advise. Thanks.

Patrick

 

[MotorCity]

A couple of suggestions:

If you have information on the structure that was supported by the piles, compare the old loads to the new loads and take a look at how long the old load was applied.

Consider performing a load test on the existing piles.

I'm not sure how a shearwall between piles would help with differential settlement. Look at a pile cap and/or grade beam arrangement instead. Hope this helps.

 

[pjheaphy2]

Thanks for the reply. I have previously researched reusing piles on their own and thats fine. The problem i have is when the new load is so large that the existing pile cannot take the capacity, even with grouting to improve capacity. The only way to combat this is to incorporate new piles with existing piles. The problem here is that a new pile and an existing pile will settle differently, thus causing problems in the foundations. I have looked at a pile cap but the new pile usually has to settle alot more than the existing pile so it causes a large tensile force in one side of the cap and a compressive force in the other. This would offset the loads on the cap thus causing an unaccounted moment in the foundation. The shear wall type structure would be treated like a deep beam restricting movement between the piles connected, so a beam arrangement could be considered. Thanks again for the reply.

 

[SlideRuleEra]

pjheaphy2 - Mixing new piles and old piles works well, if done properly. For example, when certain existing bidges are widened new piles are driven outboard of the existing piles and the pile caps are extended.

The key to success is having a pile cap (or foundation, if it is a building) that is a tradional, but conservative, design that can withstand unexpected pile load distributions. If this is accomplished, you don't get differential settlement; you force all piles to settle the same amount. The result is that some piles carry more load than others; with information gathered by load testing, as suggested by Motor City, this can be compensated for.

http://www.SlideRuleEra.net

 

[emmgjld]

A lot depends on what you know about the existing piles, to include their age and physical properties. It may be possible to restrike these piles and have a confirmation of the set. Of course, Dynamic Testin, with the restriking, is strongly recommended.

If the piles are not up to snuff, the pile group could be augmented with additional piles.

The design should be conservative, as per SlideRuleEra, but good data can keep the construction within reason.