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Submitted 2011-09-22 21:27:04
Any comparison of foundation repair methods must include the poured concrete piers or Bell Bottom Pier method. It was the first foundation repair method developed to stabilize concrete slab foundations. It was developed in the 1960s and its primary disadvantages are higher cost and longer construction time. However, this method has impressive advantages. It is based on the same construction concept that is used to build support columns for highway overpasses and bridges. It is a thoroughly researched concrete slab repair method that is recommended by the vast majority of structural engineers. Large holes are dug under the areas that need foundation support. The footprint, or diameter of the base of the pier is 22 inches, which is significantly larger than the six inches for concrete piles and the three inches for steel piles. Concrete is poured into the holes and steel rebar is placed in the wet concrete. When the concrete has cured the home or commercial building can be leveled. The Bell Bottom Piers are extremely strong and will resist horizontal and vertical soil movement. It is the most permanent foundation repair method available.
In the 1980s a faster and lower cost method of foundation repair was developed called concrete pressed pilings. It is the simplest and lowest cost of all the methods of foundation repair. It is still used today primarily because it can be completed in a short amount of time and there is no waiting time for the concrete to cure. However, it has some disadvantages. The first disadvantage is that the process uses the weight of the home or commercial building, or a portion of it, to leverage or vertically push precast concrete cylinders into the ground. The eventual depth of the concrete cylinders is limited by both soil conditions and the weight of the home or commercial building. There is a point called the refusal point, which is the point where the weight of the home or building is insufficient to push any additional piles further into the ground. The refusal point is the limit that piles can be pushed into the soil safely, because any additional efforts could cause serious damage to the foundation of the home or commercial building. Therefore, the precast pressed pilings, which are pushed vertically, may not reach bedrock or stable soil. Another disadvantage of this method is the potential misalignment of the precast concrete cylinders during installation. There is no way to determine if piles have been pushed in the ground in a straight vertical column. They can simply ?wander? off at an angle. If the first pile hits a rock or tree root it could break or become misdirected and continue at an angle. Any of the concrete piles could fracture and break and misalign the entire column. Since the concrete piles are not connected, they could become misaligned by the natural forces of horizontal and vertical (uplift) soil movement, which is very common with any home or commercial building that is experiencing foundation problems. In addition, usually a soil test is NOT performed when using this method, and if not, the repair contractor does not know the depth of stable soil or bedrock under the customer?s property. For stable, long term foundation support it is important to reach stable soil or bedrock.
The concrete pressed pilings with insert method was developed to reduce the frequency of misalignments of the concrete pile columns. A comparison of these methods of foundation repair will reveal that they are very similar. The difference is that the precast concrete piles have a hole in the center for placement of a steel rod or cable. The steel rod, if inserted during the installation process, will help keep the concrete piles in a vertically aligned column. However, the steel rod will not prevent all potential misalignment problems. The steel rod will help the entire column resist horizontal and vertical (uplift) soil movement. However, this method does not address the other disadvantages mentioned earlier. The depth of the pushed vertical concrete piles is still limited by the weight of the home or commercial building ? the refusal point. In addition, the foundation and the home are at risk of damage if the repair crew attempts to push piles beyond the refusal point. Lastly, this method introduces a center hole in the vertical column of the concrete piles that can allow water to flow down the column and potentially weaken the surrounding soil.
The steel piling method is another version of the pressed piling method. A comparison of these three similar methods of foundation repair will reveal some improvement with this version. Steel pilings are stronger than concrete piles and can be pushed deeper into hard soil. However, the driving depth is still limited by the weight of the home or commercial building the refusal point.
And steel piling also share the other disadvantages of concrete piling. Another is potential misalignment during installation that cannot be detected. And if any of the steel pile segments is bent during installation it can not be seen. In sum, this method can create a long term loss of stability proven by experience and research.
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By: Martin Dawson
There are four major methods of foundation repair in the southern part of the United States. They are known as concrete pressed pilings, concrete pressed pilings with insert, steel pressed pilings, and poured concrete piers (Bell Bottom Piers). It should be noted that the Federal Housing Authority has not certified or expressly established approved foundation repair methods.
Any comparison of foundation repair methods must include the poured concrete piers or Bell Bottom Pier method. It was the first foundation repair method developed to stabilize concrete slab foundations. It was developed in the 1960s and its primary disadvantages are higher cost and longer construction time. However, this method has impressive advantages. It is based on the same construction concept that is used to build support columns for highway overpasses and bridges. It is a thoroughly researched concrete slab repair method that is recommended by the vast majority of structural engineers. Large holes are dug under the areas that need foundation support. The footprint, or diameter of the base of the pier is 22 inches, which is significantly larger than the six inches for concrete piles and the three inches for steel piles. Concrete is poured into the holes and steel rebar is placed in the wet concrete. When the concrete has cured the home or commercial building can be leveled. The Bell Bottom Piers are extremely strong and will resist horizontal and vertical soil movement. It is the most permanent foundation repair method available.
In the 1980s a faster and lower cost method of foundation repair was developed called concrete pressed pilings. It is the simplest and lowest cost of all the methods of foundation repair. It is still used today primarily because it can be completed in a short amount of time and there is no waiting time for the concrete to cure. However, it has some disadvantages. The first disadvantage is that the process uses the weight of the home or commercial building, or a portion of it, to leverage or vertically push precast concrete cylinders into the ground. The eventual depth of the concrete cylinders is limited by both soil conditions and the weight of the home or commercial building. There is a point called the refusal point, which is the point where the weight of the home or building is insufficient to push any additional piles further into the ground. The refusal point is the limit that piles can be pushed into the soil safely, because any additional efforts could cause serious damage to the foundation of the home or commercial building. Therefore, the precast pressed pilings, which are pushed vertically, may not reach bedrock or stable soil. Another disadvantage of this method is the potential misalignment of the precast concrete cylinders during installation. There is no way to determine if piles have been pushed in the ground in a straight vertical column. They can simply ?wander? off at an angle. If the first pile hits a rock or tree root it could break or become misdirected and continue at an angle. Any of the concrete piles could fracture and break and misalign the entire column. Since the concrete piles are not connected, they could become misaligned by the natural forces of horizontal and vertical (uplift) soil movement, which is very common with any home or commercial building that is experiencing foundation problems. In addition, usually a soil test is NOT performed when using this method, and if not, the repair contractor does not know the depth of stable soil or bedrock under the customer?s property. For stable, long term foundation support it is important to reach stable soil or bedrock.
The concrete pressed pilings with insert method was developed to reduce the frequency of misalignments of the concrete pile columns. A comparison of these methods of foundation repair will reveal that they are very similar. The difference is that the precast concrete piles have a hole in the center for placement of a steel rod or cable. The steel rod, if inserted during the installation process, will help keep the concrete piles in a vertically aligned column. However, the steel rod will not prevent all potential misalignment problems. The steel rod will help the entire column resist horizontal and vertical (uplift) soil movement. However, this method does not address the other disadvantages mentioned earlier. The depth of the pushed vertical concrete piles is still limited by the weight of the home or commercial building ? the refusal point. In addition, the foundation and the home are at risk of damage if the repair crew attempts to push piles beyond the refusal point. Lastly, this method introduces a center hole in the vertical column of the concrete piles that can allow water to flow down the column and potentially weaken the surrounding soil.
The steel piling method is another version of the pressed piling method. A comparison of these three similar methods of foundation repair will reveal some improvement with this version. Steel pilings are stronger than concrete piles and can be pushed deeper into hard soil. However, the driving depth is still limited by the weight of the home or commercial building the refusal point.
And steel piling also share the other disadvantages of concrete piling. Another is potential misalignment during installation that cannot be detected. And if any of the steel pile segments is bent during installation it can not be seen. In sum, this method can create a long term loss of stability proven by experience and research.
Author Resource:->??Martin Dawson is the co-founder (1984) of Dawson Foundation Repair. He is a leading authority in Texas and other southern states on repairing failed commercial and home foundations using the thoroughly researched drilled Bell Bottom Pier method. http://www.DawsonFoundationRepair.com/
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