steel pin piles & new foundation under old building
steel pin piles & new foundation under old building
(OP)
Existing building is on a wood foundation, ground is settling in places as much as two feet. Building has been previously jacked up to remain level however a concrete foundation needs to be installed. From everything I have read it seems that 2" steel pin piles are the way to go with 1 minute of full resistance with a 90# jackhammer. Naturally these piles have to be driven outside the perimeter of the building. What is the limit on distance from existing building? Pile caps or welded rebar? Recommended size of footing? The article below was from 2004 and has more info on this topic just not quite enough.
You might also consider the use of driven-in-place small diameter [typically 2 or 3 inch] steel pin-piles to provide underpinning support. These piles can be driven inside or outside the foundation, whichever is the most practical and least expensive. The piles should be driven to "refusal" which is defined as "less than 1-inch of pile penetration after one full minute of contimnuous driving with a 90 pound jack hammer." The piles shouold be driven as close to the perimeter of the foundation as feasible and, once driving and proof testing is completed, should be structurally connected to the exisitng foundation. The connection is typically in the form of a reinforced concrete pile cap or a continuous reinforced beam which is, where feasible, poured against and beneath the footing and is doweled into the existing foundation. If it is infeasible [or expensive] to overexcavate to install the pile caps or grade beam they can be poured against the face of the foundation and/or stem wall and then structurally doweled in-place.The pin-piles should be installed at approximately 4' - 0" center-to-center spacings and each should be capable of developing well in excess of four thousand (4,000) pounds in axial capacity provided the refusal criterion has been met.Research we have performed indicates that if the refusal criterion is met axial load capacities in excess of twenty thousand pounds can be achieved. If the piles are relatively short and/or are surrounded with reasonably firm soil [soil that may be compressible, but not junk]they should not be subject to any significant lateral loading or lateral deflection. This underpinning system has been used extensively in the Pacific Northwest for many years with virtually no detrimental impact. One of the advantages is that you can limit the amount of overexcavation and backfilling, and all the equipment is man-portable a useful point in constrained access sites.
You might also consider the use of driven-in-place small diameter [typically 2 or 3 inch] steel pin-piles to provide underpinning support. These piles can be driven inside or outside the foundation, whichever is the most practical and least expensive. The piles should be driven to "refusal" which is defined as "less than 1-inch of pile penetration after one full minute of contimnuous driving with a 90 pound jack hammer." The piles shouold be driven as close to the perimeter of the foundation as feasible and, once driving and proof testing is completed, should be structurally connected to the exisitng foundation. The connection is typically in the form of a reinforced concrete pile cap or a continuous reinforced beam which is, where feasible, poured against and beneath the footing and is doweled into the existing foundation. If it is infeasible [or expensive] to overexcavate to install the pile caps or grade beam they can be poured against the face of the foundation and/or stem wall and then structurally doweled in-place.The pin-piles should be installed at approximately 4' - 0" center-to-center spacings and each should be capable of developing well in excess of four thousand (4,000) pounds in axial capacity provided the refusal criterion has been met.Research we have performed indicates that if the refusal criterion is met axial load capacities in excess of twenty thousand pounds can be achieved. If the piles are relatively short and/or are surrounded with reasonably firm soil [soil that may be compressible, but not junk]they should not be subject to any significant lateral loading or lateral deflection. This underpinning system has been used extensively in the Pacific Northwest for many years with virtually no detrimental impact. One of the advantages is that you can limit the amount of overexcavation and backfilling, and all the equipment is man-portable a useful point in constrained access sites.





RE: steel pin piles & new foundation under old building
There may be a lot more to this than meets the eye with 2 feet of settlement. That is extremely high.
I would strongly recommend getting a geotech and structural engineer.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: steel pin piles & new foundation under old building
RE: steel pin piles & new foundation under old building
RE: steel pin piles & new foundation under old building
Might want to place the grade beams well below the finish grade and extend a stem wall up to above grade to allow for future settlement of the surrounding soil.
However, I would still consult a geotech and structural engineer to design the total foundation system.
Are there any methane issuues here from decomposing vegetative material?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: steel pin piles & new foundation under old building
There are no known methane issues but as of yet no geotech professionals have been consulted. I like your ideas about pouring subgrade, Thanks Again for your time-
RE: steel pin piles & new foundation under old building
When designing the grade beams, I generally make them so that nothing more than nominal stirrups are required, if any. Being in Alaska, with the high seismic criteria, you may have to provide stirrups anyway.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: steel pin piles & new foundation under old building
(a) do boring and or probes using hand driven equipment to get some ideas of what you will be driving the pipes thru, and at what depth to expect approach to refusal. Good bearing elevation will change very fast, given your bedrock/fill situation.
(b) think about the way the pipes will be coupled. It's not a trivial issue. Threads can strip and make it difficult to drive the next pipe. Every pipe driver has his own favorite splice device. Point is, I recommend that you get a geotech and/or structural eng to work with you, who has done this stuff before, and knows the pitfalls.
(c) I have used a max working load of 7000 lb per 2" pile for about 30 projects with no problems. Pipes are driven to refusal as defined by others above. Good Luck.
RE: steel pin piles & new foundation under old building
Steel grade: SPHC, 08AL, 08F, HG5, DF08, Q195-235, M8
Standards: ASTM, API, JIS, DIN, EN, BS, GB
RE: steel pin piles & new foundation under old building
RE: steel pin piles & new foundation under old building