What is a pier? How does that differ from a pile?
The two terms are often used interchangeably. A pier is defined as a deep foundation system that is used to support a structure. The weight of the structure is transferred through the pier to a stable soil mass or bedrock. A pile is a deep foundation system, consisting of relatively long, slender, column members driven into the ground (Steel, timber, reinforced concrete) that may terminate with a cap on top, referred to as a pile-cap. Piers are often referred to as single support structures while piles are often a combination of piers resulting in a common “cap” to provide collective support.
Do I need an engineer to evaluate the need for underpinning? If so, how do I find one in my area?
A trained and qualified foundation repair expert or a qualified Professional Engineer is the best person to evaluate and recommend a proper design of repair. As your representative, the engineer evaluates the most cost effective and permanent solution to meet your needs. Your A. B. CHANCE Certified Installing Contractor has names of engineers in your area who are familiar with soils and designing underpinning repairs. Often, your CHANCE Contractor will have a professional engineer on staff or on retainer. Another source would be your local chapter of the American Society of Professional Engineers
Do I need to go to the expense of having a soil boring?
Soil borings and geotechnical reports are the best method to determine the bearing capacity of the soil. This is the preferred method to determine the required pile depth necessary to reach competent load bearing soil. It is important that the pile is installed beyond the active zone of seasonal wetting and drying. In the active soil zone expansive clay soils can shrink or swell, based on moisture content, which can cause improperly installed piles to fail. A soil boring is not the same as a shallow test pit. Test pits are excavated areas 8 to 10 feet deep, which will generally provide soil information about the upper layer of soil. When ordering a soil boring, ask the geotechnical engineer for a standard penetration test, which goes to refusal, or strata that will support two times the weight of the structure. Your A. B. CHANCE Certified Installing Contractor has names of engineers in your area who are familiar with soils and designing underpinning repairs. Also, your CHANCE Contractor may have a professional engineer on staff or on retainer.
How deep do Helical Piers need to go?
Helical Piers need a minimum of 5 feet of soil above the top helix and need to be deeper than the active zone of soil, which is the zone of seasonal wetting and drying. Also, the Helical Pier needs to achieve the torque (turning or twisting force) specified on the plan of repair. Torque will vary based upon depth and density of the soil.
How many piers do I need to support my house?
All piering applications need to take into consideration:
- The weight of the structure
- The structural integrity of the foundation footing and wall
- The strength of the soil
- A safety factor
Most typical residential homes will require piers to be spaced 5 to 8 feet apart.Your engineer or Certified Foundation Specialist can best answer this question for you.
Do I need to pier the entire house or only that portion which shows signs of settlement?
A qualified professional engineer is the best person to evaluate what is required and determine a design of repair. It is important to determine the cause of the settlement and the potential for future differential settlement. Typically, if the entire structure was constructed on weak or expansive soil, it would be prudent to pier the entire structure. However, if only a section of the structure is in distress, it is wise to pier that part which is most in need of repair.
I don’t see any visible signs of settlement; should I be concerned?
All structures are subject to the different types of soil on which they are built. Clay soils will expand and contract as they gain and lose moisture. Soil characteristics can change from one neighborhood, or one house, to another. Building weights, subsurface erosion, buried organic materials that decompose, can also change the ability of the soil to support the structure. Moisture-filled soils, which freeze, can create uplift problems. Some warning signs of possible settlement problems include: doors and windows that stick, doors out of square, not plumb, or doors that won’t remain open or closed; cracked plaster walls, ceilings, or torn drywall, baseboard and molding that pulls away from the wall, floor, or ceiling cracks, cracks in concrete basement and crawl space walls, as well as “stair step” cracking of concrete block or brickwork. All are signs of foundation settlement. Be observant and aware of changes in your house or structure.
There are several companies offering Helical Piers. Are they all the same?
No. There are significant differences between these companies, the helical products they offer, and the A. B. Chance Company products. Several manufacturers have introduced products that compete with the A. B. Chance Company, and some of these products LOOK the same. The consumer has a hard time telling the difference. The following are a few examples of how the buyer can be deceived:
- A. B. Chance products are Class B-1 hot-dipped galvanized in accordance with ASTM A153 (American Society for Testing and Materials). Competing manufacturers offer products as “galvanized” which in many cases means they were powder coated. Powder coating is NOT the same as hot-dipped galvanization and does not provide the same corrosion protection. Hot-dipped galvanization penetrates the steel surface and is not just a surface coat.
- A. B. Chance Company extensions are constructed with a forged coupling. Some competing manufacturers weld oversized stock to form coupling joints to accommodate extensions.
- A. B. Chance Company products are all welded in accordance with AWS (American Welding Society) standard D1.1. All A. B. Chance welders are certified to AWS standards. Competing companies state that their products are welded in accordance with D1.1 standards, but they fail to identify their workers as Certified Welders.
- A. B. Chance Helical Piers and Anchors are manufactured to the International Standard Organization (ISO) 9001 Certificate No. 001136. This is a manufacturing standard which means that the material used to manufacture Chance Helical Piers and Anchors is NEW, UNUSED and traceable to the steel mill of origin. This is a building code requirement for deep foundations (Uniform Building Code and the International Building Code). Chance products carry a manufacture and heat treat number on each item and section. There are other manufacturers who do not comply with the code requirements because of the method of manufacture.
- A. B. Chance Helical Piers have been thoroughly evaluated and approved for code compliance in the building industry as described in the following reports
- International Congress of Building Officials (ICBO), Engineering Report 5110.
- Building Officials and Code Administrators (BOCA) Evaluation Service, Research Report 94-27.
- Southern Building Code Congress International (SBCCI), Report No. 9504B.
Competing manufacturers reference these independent evaluation services in their literature, but they don’t provide the research report number.
What other types of piers are available for underpinning?
There are a number of companies that have systems that are marketed as solutions to underpinning properties. The key to the success or failure of any underpinning system is the type of soil conditions to which it must perform and its ability to provide a factor of safety. Any underpinning system must be able to withstand changes of moisture within the active zone of soil, and the system must be able to resist unexpected additional loads. As an example, there is a piering product referred to as a push pile or pipe pier. This particular system consists of a pipe, which is pushed hydraulically into the soil by using the weight of the structure as a resistant load. This type of pier works well if it is advanced to bedrock or hard shale, but it is not practical in clays or organic material. In clays or organic material it may remain subject to the active zone of soil and it cannot be installed with a factor of safety. The force of installation is derived from the weight of the house, so the completed resistance to failure is 1:1; the pipe’s stability (resistance to load) is equal to the weight of the structure. If a snow load is added to the roof during the winter, or a change of permanent fixtures increases the weight of the structure, the pipe pier is subject to failure. Other piering systems include grout or cement injection, concrete blocks, timber piles, even stone or brick, placed under the existing footing after excavation. Since these systems are placed within soils areas of unknown strength, they are all subject to failure. They are a temporary solution at best.
What are the advantages of a Helical Pier?
Helical Piers are true end-bearing piers. The weight of the structure is transferred to the helical plates. Helical Piers are installed independent of the structure and do not rely on the weight of the structure for installation. This prevents shaking or moving of the structure. Helical Piers are installed to a known capacity and a known competency of soil. This means that the helical pier can be installed with a factor of safety (most often 2 times the dead and live loads of the structure) and terminated in a soil strata or bedrock capable of supporting the load. Unfortunately, push piles cannot do this unless they are resting on rock.
What documentation should I ask for as part of the installation contract?
In addition to the plan of repair, you should require the contractor to provide a signed pier log, which needs to contain:
- Project name and location
- Name of contractor or responsible party with complete address and telephone number for contact.
- Date and time of the installation.
- Location and reference number of each pile.
- Description of lead section and extensions installed at each pier location.
- Overall depth of installation, as referenced from bottom of grade beam or footing.
- Torque reading for the last three feet of installation, or the torque reading at the time of pier termination.
- Any other relevant or pertinent information relating to the installation.
- Name of the trained and certified installing technician(s).
Should I lift the structure back to the original elevation?
The A. B. Chance Helical Pier Foundation System is designed to lift. However, there are a number of factors that must be considered before performing a lift. Has there been corrective work performed prior to the pier installation? Have replacement doors and windows been installed? Has mortar, caulk or molding been installed to hide cracks and gaps? Lifting the structure after the repairs have been made will cause more damage. In these cases it would be better to stabilize the structure and avoid the lift. Stabilizing means that the weight of the structure is transferred to the piers without lifting the structure.
How should I select a contractor for the installation of Helical Piers?
The A. B. Chance Company requires contractors to be certified by Chance Company Instructors for installation of the Helical Piers in underpinning applications. This requirement is in accordance with the Chance Company’s quality assurance program as outlined by the International Standards Organization (ISO) 9001, Certificate No. 001136. The Chance Company commitment to quality controlled product and quality controlled installation is your assurance of a job well done. No other piering company requires such quality assurance from product to installer.
How are the Helical Piers secured to the foundation?
A. B. Chance Company specifies that their underpinning bracket is dry-packed with non-shrink grout to ensure proper bearing and to avoid point loading which could damage the footing and foundation. Two holes are then drilled into the foundation through the mounting bolt slots of the bracket. The underpinning bracket requires two anchor bolts with 3,500 lbs. of tension capacity. This restricts any potential movement of the bracket thus ensuring continuous alignment of the pier and footing.
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