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.
