Foundation Stabilization Piers
Post installed stabilization piers are the most common solution prescribed for a settling foundation. There are two basic types, concrete and steel. The preferred type depends on the property soil conditions and accessibility.
Concrete piers are shown in the picture to the left. The concrete pier system is composed of drilled concrete piers (designed by a professional foundation engineer) with a special bracket that attaches directly to the footing under the foundation walls. This bracket then has the capability of lifting or jacking the footing or wall back to its level position if necessary. If post-installed piers are only required to prevent future movements, then the piers are tightened under the footing.
Advantages to Concrete Piers:
Disadvantages to Concrete Piers:
Helical piers are shown by the picture to the right. These systems are typically composed of a anchoring rod (as shown above) and a foundation bracket. The anchoring rod has an anchoring screws (number required by analysis) that propel the rod into the ground. Upon reaching the appropriate torque resistant based on the calibrated ground properties, the helical pier installation is complete. The brackets are then installed and the procedure is similar to that described above for the concrete pier system.
Advantages to Helical Piers:
Disadvantages to Helical Piers:
Push Piers are similar to helical piers. However, push piers are designed to lift a house into a level position upon installation. Push piers, hence the name, are pressed or pushed into the ground by a hydraulic pump. The piers are typically installed along a wall. In most cases, the entire house is retrofitted with these piers to achieve an equal force distribution along the foundation. Once in place, the foundation brackets are attached beneath the footing or foundation wall. Hydraulic pumps then push the piers into the ground until an acceptable load level is reached. As mentioned before, in many cases, entire house foundations are retrofitted at one time. Therefore, all the piers are hooked to the hydraulic pump at one time to ensure even force distribution.
Advantages to Push Piers:
Disadvantages to Push Piers:
Wall Tiebacks are commonly used to restore structural integrity to basement or retaining walls that have been over-stressed or overloaded by lateral earth pressures. As the wall begins to bow under the earth and soil pressures, it begins to crack horizontally. There are many less invasive techniques that may be introduced to prevent or reverse further wall movement, however the wall tieback system is highly regarded as the best alternative under most conditions.
Wall tiebacks are basically rods that are anchored into the ground. There are many different techniques that have been successfully used in the past for rod anchoring. In most cases this requires digging behind the wall for securing the anchors. Metal rods are inserted through holes in the walls, then directed to an excavated area of the yard where a large plate can be attached. This plate is what produces the pullout resistance. The metal rod has another plate at the wall end, which is secured by a nut and bolt assembly that can be tightened until the wall has reached its desired position.
Waterproofing and drainage are very important factors in the overall durability and structural integrity of soil retaining walls. To begin, there are typically two methods for reducing water flow through a wall, waterproofing and damp-proofing. Damp-proofing is a method used on less sensitive walls, which is basically a painted or sprayed material that sticks to the wall and once dry, increases the water resistance of the wall. The second method, waterproofing, is a technique that uses a membrane (as shown to the right), which when installed properly, prevents water from passing to the wall completely. The method of water prevention will depend on the sensitivity of the interior space and the wall use.
Drainage is key to a successful and long lasting wall design. When water accumulates behind a soil retaining wall, unexpected pressure builds and may crack the wall allowing water to pass through. However, if the wall is properly waterproofed and has improper foundation drainage, the structural integrity of the wall may be comprised. Therefore, it is always a good idea to consult a professional engineer before construction begins or anytime after if you suspect an issue.