Many structures, such as residential homes and low rise buildings, are constructed on foundations that are not in direct contact with a stable load bearing underground stratum, such as, for example, bedrock. These foundations are typically concrete slabs or a footing upon which a foundation wall rests. The footing is generally wider than the foundation wall in order to distribute the structure's weight over a greater surface area of load bearing earth. Therefore, the stability of these structures depends upon the stability of the ground underneath or supporting the foundation. With time, the stability of the underlying soil may change for many reasons, such as changes in the water table, soil compaction, ground movement, or the like. When the stability of the support ground changes, many times the foundation will move or settle. The settling of a structure's foundation can cause structural damage reducing the value of the structure or total property.
For instance, structural settling can cause cracks in foundation walls, as well as unsightly cracks in the interior or exterior of building walls and floors. In addition, settling can shift the structure causing windows and doors to open and close properly. Inventors have recognized the foundation-settling problem and have developed various devices and methods to correct its effects.
One common device and method to correct foundation settling consists of employing hydraulic jacks in conjunction with piers to lift the foundation. Piers, also known as piles or pilings, are driven into the ground by hydraulic mechanisms until the pier reaches bedrock or until the pier's frictional resistance equals the compression weight of the structure. Once these piers are secured in a stable underground stratum or several stable underground strata, further lifting by the hydraulic jacks raises the level of the foundation. When the foundation is raised to the desired level, the piers are permanently secured to the foundation. The hydraulic jacks are then removed. This method of correcting the level of a foundation generally requires the excavation of a hole adjacent to or underneath the foundation in order to position and operate the lifting equipment.
Steel piers are well known and exist in many varieties. One common type of a pier is a straight steel pier that is driven down until it reaches bedrock or stable soil weight bearing layer. These straight steel piers are rammed straight down into the ground. Another style of pier known to the art is a helical pier. On the end of a long pier shaft is a large helix. This helix distributes the weight of the pier over a larger surface area of soil making it a highly desirable pier structure to use. Unlike straight piers that are driven straight through the earth, it is necessary to screw the helical piers into the earth by rotating the pier shaft.
Steel piers currently known in the art are predominantly directed toward only addressing the problem of settling, that is the downward movement of the structure due to various environmental conditions, which are primarily hydro-geologic in nature. These steel piers that are designed to only address settling problems have an extremely high level of mechanical stability when supporting the downward load of the building foundation. However, these steel piers are generally not configured to remain stable under a sheer condition where the building moves laterally with respect to the pier and surrounding earth. Further, these piers are generally not configured to remain engaged to and support a building when the surrounding earth rises and pushes the building upward.
During the lifespan of a building, the building foundation may experience more than just the downward movement caused by settling. In a seismic event, the earth can move vertically, called uplift, as well as laterally. Other geologic phenomena such as landslides, or mudslides (common in southern California) can also produce lateral movement of ground supporting a building foundation. Buildings supported by steel piers configured to address only settling commonly fail when the surrounding earth undergoes lateral or vertical movement, resulting in serious damage or complete loss of the supported building. Consequently, there is a very distinct need in the art to develop an improved pier design that can support a building under lateral and vertical ground movements as well as settling.