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Foundation Failures - How They are Repaired & Choosing a Contractor
HPW Article Archive
By George Runkle, P.E.
Unfortunately, many houses suffer from various forms of foundation failure. When constructing foundations, it 's important that the foundations be placed below the frost line, and on natural soil, or properly compacted fill. You have to make sure there is no buried organic material or trash under the foundations. In areas where there are expansive clays, it 's important to get the foundations deep enough that seasonal changes in moisture won't cause them to heave.
Often when constructing houses, builders will get sloppy. They will place foundations on fill that hasn't been compacted, or on top of buried trees and other junk. When this happens, it 's necessary to perform a repair. You generally have three basic methods to do the repair:
Pressure grouting (also called mudjacking), where a cement and sand mix is injected under the foundation with high pressure.
Helical piers, which are large augers that are drilled down beside the foundation, and held to the foundation with a bracket.
Resistance piers, which are pipes that are pushed down into the soil beside the foundation, the foundation is used as a brace to push the piers down.
There are advantages and disadvantages to each one of these methods. Generally, pressure grouting is good for fixing concrete slabs. Helical piers are good for lighter weight structures where you don't have enough weight up against for resistance piers. Resistance piers are excellent for heavier structures, and also you can actually jack the structure back up in many cases correcting the original damage.
If you have foundation failure, the biggest problem that you will have (other than the expense) is finding a contractor. You will get wildly varying solutions proposed by contractors, some will be just trying to sell you a system and make as much as they can. Generally, I recommend hiring an engineer first. Again you have to be careful - what will the engineer include in his or her fee? Insist that you get a design as part of that fee. Some engineers will give you a long and detailed report that tells you all about the geology of your area, how your house was constructed, and a lesson in soil mechanics. Then it will tell you in many words "you need to have it fixed somehow". Don't accept that. Get a signed agreement with the engineer prior to the services that says what you will get and what the fee is. Also, the engineer should provide you a list of qualified contractors.
If you don't go with an engineer first, then get a number of contractors to look at the foundation that has failed. The honest ones should come to about the same conclusions, so you can throw out the proposals with the extreme repairs. Also, throw out the extremely low priced bids.
Also, look for these items:
Piers must be placed no more than 5 - 6 feet apart on foundations (foundations can not span farther than that). The piers must be evaluated by the ICC Evaluation Service. Don't accept a contractor with home made piers.
With pressure grouting, the contractor needs to inject the grout deep in the soil, not just fill the void under the slab. In fact, pressure grouting is so tricky, don't do it without getting a good recommendation for the contractor.
The contractor should have been in business for a long time too. Don't be his or her first customer.
This is a very short summary of what has to be done. Please visit Runkle Consulting for more definitive information.
About the Author:
George Runkle, P.E. is a structural engineer in Atlanta, GA, and a graduate of the University of Maryland with a Bachelor of Science in Civil Engineering. He has been in the construction industry for 31 years, 27 of them as an engineer. His company, Runkle Consulting, Inc. provides various structural engineering services, including foundation failure investigation. His web site can be found at Runkle Consulting.