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Foundation Engineering,  

Concrete Press Piles Foundation Repair: Building Code non-compliance Part 2

b) Stabilization

Here’s the definition of the code for stabilization of foundations:

1808.6.4 Stabilization. Where the active zone of expansive soils is stabilized in lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be stabilized by chemical, dewatering, presaturation or equivalent techniques.

Many foundation repair companies like to use the word stabilization a lot whenever these concrete press piles are used. However, as shown above, the code clearly defines stabilization as improving the soil if a good foundation system (code approved piles or piers) or removal of soil is not done.  

Therefore, according to the code, stabilization of a foundation (a new foundation or existing foundation, i.e. foundation repair) means stabilization of the soil (i.e. improvement of the soil where the foundation is bearing) through:

  •  Dewatering: As the name implies, removing water (moisture) from the soil, draining the soil. If the soil is always dry, then it cannot move because there is no change in moisture content in the soil. Usually this dewatering operation of the soil is accomplished through installation of enough wells (and pumps) around the foundation. As you can see, this method is not very easy (or cheap) to implement and monitor, so dewatering of soil as a foundation repair method or as a new foundation construction method is not common. It is possible to do it in San Antonio, Austin, and Dallas, but Houston would not be a smart solution because the water is already close to the surface.
  • Pre-saturation: The exact opposite of dewatering. Soil is injected with water so that the soil is saturated. In other words, the soil has so much water that it cannot retain more water (just like a sponge, after a while, the sponge won’t retain any more water). Since the soil already has all this water, more water will not make a difference, which means the soil won’t make the foundation move because it’s already wet. Of course, since changes in moisture content in the soil is what makes the soil move, and move the foundation bearing on that soil, then the main concept with pre-saturation is that once water is injected into the soil, then something needs to done to ensure that soil stays wet. Usually, this is achieved by adding really deep beams around the foundation, or horizontal or vertical moisture barriers. This type of foundation repair method is sometimes feasible, and definitely substantially more common than dewatering.
  • Chemical Injection: Chemical injection, as the name suggests, consists in injecting a concoction of chemicals that change the chemical composition of the soil. For expansive soils, the chemicals added make the soil repellent to a certain degree to changes in moisture content so that expansion and shrinkage of the soil is greatly minimized. By the way, this is often the Preferred foundation repair method in the commercial construction world because it’s reliable, quick, and not very intrusive. It’s also very expensive and so not very popular in the residential foundation repair industry. We should say that a foundation repair that involves chemical injection requires heavy machinery… if you are offered a foundation repair system for your house that involves chemical injection and you are charged just a couple of thousands of dollars and the foundation repair contractor shows up with hand held devices, then we can guarantee you what they are doing will only slightly help your foundation. If you live in San Antonio or Austin or Dallas, the chemicals would need to go do to about 15 feet; at this depth, the pressure is so high, there is no hand held device that can inject the soil (and definitely not for a few thousands dollars). In Houston, the depth required is slightly shallower because of the shallow water table.
  • Equivalent techniques: These are techniques similar to the soil stabilization techniques discussed above, mainly, that the soil or soil conditions are improved in some way so that changes in moisture content are kept constant.

 

Next Page: Foundation repair concrete press pile Building code non-compliance Part 2: c) Why this foundation repair system doesn't meet the code


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