Repair Methods for Foundation Settlement or Vertical Foundation Movement
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How to Repair Vertical Foundation Movement or Foundation Settlement
Illustrations of foundation settlement or sinking repairs using slab jacking, driven steel pins, helical or "screw piers", friction piers or piles and foundation reconstruction.
Photographs and sketches of alternative foundation cracking or settlement repair methods
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This website discusses How to Repair Vertical Foundation Movement or Foundation Settlement
using methods to stabilize or even level and straightened a settling or moving foundation wall or floor slab, by using
slab jacking, driven steel pins, helical or "screw piers", friction piers or piles or even foundation reconstruction.
Repair Methods for Vertical Foundation Movement - Foundations, slabs, fireplaces, chimneys
In the photos shown here, substantive cracks appeared and continued to increase in size in this poured concrete foundation
used to support a modular home which had recently been completed.
The cracks and foundation movement were probably due to
a combination of: poorly prepared foundation footings, blasting on an adjacent building lot to prepare that site for new construction,
and possibly omission of steel reinforcement in the poured wall. As movement appeared to be ongoing over more than a year,
the builder might have repaired the foundation by supporting it from below using one of the methods listed here.
Foundation Repair Using Mud Jacking, Pressure Jacking, Slab jacking Methods
Grout pumping or mud jacking is used to stabilize soils below settling footings or slabs.
The mud jacking or grout pumping method of foundation repair is capable of lifting
a slab and possibly some structures.
Mud jacking is suitable if bearing rock or stable soils are not too deep.
For cases
where bedrock or suitable stable soils are deeper, slab-jacking methods are usually preferred - see the next foundation
repair item just below.
Slab jacking is used to stabilize or lift and level settling concrete slabs, including interior floor slabs poured within the perimeter
of a building foundation, and also lifting and leveling of monolithic concrete slabs or slab-on-grade construction.
If
a floor slab or slab on grade construction is tipped, settling, or cracking, the underlying cause may vary among
poor site preparation such as pouring over un-compacted fill, poor surface water runoff control resulting in soil
loss or compaction, expansive clay soils, soil subsidence over buried debris, and sinkholes.
Sketch of mud jacking or pressure grouting to lift and repair a concrete floor slab
Carson Dunlop's sketch shows how slab jacking or mud jacking, also called pressure-grouting, might be used to repair a settling
garage floor slab.
Foundation Repair Using Driven Steel Pins
Driven steel pins are used to stabilize settling foundation walls or footings. A pin is driven next to the foundation and is
inserted into the soil until it contacts bedrock.
The driven pin foundation repair method, like the
alternative piers listed below, is often used when a portion of a foundation wall is moving or settling, perhaps
because of improper site work or footing undermining.
The cost of this method is about $1200. to $1500. per pin for average 30 ft. depth.
The steel pin foundation repair method permits more precise leveling control across the building than grout pumping.
Some reviewers expressed a concern
about a possible durability problem? The manufacturers typically warrant the product for 60 years.
[Sketch courtesy of Dwyer, Magnum Piering, Florida, via ASHI Seminar 1998, edited by DF.]
Helical Pier or Screw-Pier foundation Repair for Settled Footings, Slabs, or Walls
A.B. Chance helical screw piers are an approach similar to the above, but may be shorter in length and useful where soil conditions
do not provide shallow bedrock or won't work well with friction piers (below).
Helical piers to repair sinking foundations are
often used in building repair or reconstruction, and include models which can be used to level floor slabs as well. Sketch courtesy Carson Dunlop.
Friction-Pier or Driven Pier Foundation Repair for Settled Footings, Slabs, or Walls
Friction piers or Magnum piers or foundation piles for foundation repair are driven piles which rely on soil friction against the sides of the pile to prevent further settlement.
This method was used with modest success at a spectacular settlement case of the settlement of the Victoria, an enormous masonry hotel
on the harbor at Vancouver Island, Canada.
The Vancouver Victoria hotel was built over a marsh and set on friction piers. When we visited the site
in the 1980's the hotel had settled fairly uniformly (luckily) so that the building has remained useable.
But today visitors
enter the building on its second floor! The friction pier approach was not adequate in this case. Sketch courtesy Carson Dunlop.
Rod & Steel U-Channel or I-Beam Foundation Repair for Settled Footings, Slabs, or Walls
Rod & Channel Repair to Stabilize Structures over Poor Soils. Carson Dunlop's sketch of steel rods and "U" channels illustrates how an engineer may specify a repair to stabilize a building which has been constructed over un-stable soils.
Rod and u-channel structural repairs are more likely to be used where soil conditions prohibit the other pier or jacking methods illustrated above.
Threaded steel rods are run through the width or length of the damaged structure and bolted to vertical steel U-channels on the building exterior.
You may see a similar use of through-building threaded steel rods in 19th century masonry buildings in an attempt to stabilize structural masonry walls. Instead of "U" channels the rod ends are mounted through steel plates, often in a decorative shape.
Foundation Repair of Settled Footings, Slabs, or Walls by Reconstruction
Reconstruction of foundations: Some engineers who examine a failing foundation may prescribe excavation and reconstruction, possibly with reinforcement over the original
design and with additional foundation and site drainage. We saw this method used for a home in Hyde Park, New York when it was
discovered that the home had been built half over a landfill and was suffering from substantial differential settlement.
Helical screw
piers or even driven steel pins might have worked at about one tenth the cost of the project as it was designed. We don't know
if that alternative was considered.
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Additional technical contributors & reference sources for this article are listed below.
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ADDITIONAL READING about Foundation Failure Diagnosis & Repair
Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but reprints available from some inspection tool suppliers)
Design of Wood Structures, Donald E. Breyer, McGraw Hill, 1988 ISBN 0-07-007675-8
Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
ASHI Training Manual - not recommended: incomplete, inaccurate, overpriced--DF
The Home Reference Book and other Manuals from Carson Dunlop, Home Pro, T.I.E., Inspection Training Associates (Home Inspection training/report firms)
"Avoiding Foundation Failures," Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
"A Foundation for Unstable Soils," Harris Hyman, P.E., Journal of Light Construction, May 1995
"Backfilling Basics," Buck Bartley, Journal of Light Construction, October 1994
"Inspecting Block Foundations," Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
"When Block Foundations go Bad," Fine Homebuilding, June/July 1998
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NOTE: Journal of Light Construction articles are available on CD ROM from the Journal of Light Construction, www.bginet.com, 802-434-4747
Authority
Opinions herein are the responsibility of the author. Most of this material has been subject to ongoing peer review but is without any professional engineering analysis. Home inspections may include the discovery of defects involving life, safety, and significant costs. Home inspectors who are not both qualified and certain of the authoritative basis of their conclusions should obtain their own expert advice from qualified experts.
This work is also based on the author's construction & inspection experience, training, research, and survey of material from ASHI, and from N. Becker, R. Burgess, J. Bower, D. Breyer, A. Carson, J. Cox, A. Daniel, M. Lennon, R. Peterson, J. Prendergast, W. Ransom, D. Rathburn, E. Rawlins, E. Seaquist, and D. Wickersheimer. Some useful citations are at the end of this paper.
Sal Alfano - Editor, Journal of Light Construction*
Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and some of the foundation inspection photographs cited in these articles.
A.B. Chance foundation repair systems, helical piers, foundation repairs www.abchance.com
Dwyer of Florida, supplier of Helical Piles, foundation repair, and concrete restoration in Florida, exclusive dealer for Magnum piering. This company provides helical piles, foundation settlement repair, concrete restoration, shotcrete, pressure grouting, and slabjacking for residential and commercial buildings. 1-866-900-PIER www.dwyerflorida.com
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Repair Methods for Foundation Settlement or Vertical Foundation Movement
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