There are several types of piers or pilings that work well depending on a number of factors including the extent of damage, the age and condition of your foundation and the predominant type of the soil in your area. Contact a foundation engineer or other expert to help you identify your individual needs.
Most foundation repairs will be accomplished by installing piers of various types under your foundation to raise and support it. The heavier the structure the more closely the piers must be spaced. Remember inside corners are heavier than outside corner and load bearing walls are heavier than non-load bearing walls.
The greatest numbers of piers are usually required along the perimeter of the foundation due to weight and this is where failure generally occurs. If the interior area of the foundation is also sinking or shifting, piers may be necessary there too.
The total number of piers, and where they are placed, will also depend on the extent of failure, weight of the supported structure, condition of the foundation, and the type of pier you decide to use. Each of them has their benefits and situations where they shine.
The method of repair is a decision you will have to make. You must decide based on the information you research, advice from foundation engineers and experts, along with common sense. It is an important decision that should not be taken lightly. You will be deciding on the fate of your most valuable asset.
Steel Push Piers Known as push piers, resistance piers, micropiles or steel pressed piers, these underpinning products are driven hydraulically into the soil using the structural weight of the building as a reaction force.
A friction reduction collar is attached to the lead section of the pier pipe. The purpose of this collar is to create an opening in the soil that is larger in diameter than the pier pipe. This dramatically reduces the skin friction on the pier material as it is driven into the soil. This feature allows the installer to load test and verify that the pier has encountered a firm load bearing stratum or rock that is suitable to support the designed load.
Each pier is driven individually using the weight from the structure and any soil loads available . Driving several piers side by side would make the resistance pier system totally ineffective. After each pier is driven to this load bearing stratum a lift assembly is attached to each bracket placement to initiate a stabilization or lift. Individual 10,000 psi hydraulic lift cylinders are inserted into these lift assemblies and then attached to a manifold for a synchronized lift. This synchronized lift is a key component to a high quality push pier system. Opposed to systems that use bottle or car jacks that apply uneven pressure to your foundation, a synchronized system uses a manifold and hydraulic cylinders designed for structural lifting.
Steel piers can reach much greater depths than pressed or drilled which allows them to be founded below active soils. Any pier system that does not penetrate beyond these active soils should be avoided at all costs. This type of pier is well suited for most areas, with the exception being areas where a load bearing stratum is too deep to cost effectively justify their use. These piers have been used for decades with great success. While they require a large amount of training and supervision by foundation experts resistance piers are a very reliable choice for many situations.
Advantages High ultimate capacities (up to 99,000 lbs.)
Great lifting capacities
Installs from inside or outside of structure
Installs with little or no vibration
Requires minimal soil removal
Can reach greater depths than other types of piers
100% of piers are field load tested
Minimal effects on landscaping
Helical Piles Known as helicals, a helix pier, screw anchor or ground anchors these also are steel underpinning products used to support foundations. In new construction they are used in the place of “old fashioned” drilled concrete piers. In foundation repair they are used to support existing structures when attached to a bracket. In both situations they are hydraulically turned into the soil with a high torque gear motor. Simply put, the amount of torque required to install is directly correlated to their capacity.
The helical pile consists of a shaft fabricated of either square steel bar or tubular steel. Welded to the shaft are one or more helical plates. Typically the plate diameters increase from the bottom of the shaft upward and are spaced a distance of three times the diameter of the plate directly below. Shaft lengths generally vary from 5' to 10' with extensions added to achieve required depth. Foundation brackets are then installed to allow for the load transfer from the foundation element to the helical.
Due to their bearing plates, generally helical piles do not need to be installed as deeply as resistance piers. They must be installed below the active soils though. Generally a foundation engineer predetermines a target depth and torque for the piles to be installed. This depth is determined by the helical configuration, the soil conditions and the linear foot weight of the structure.
Once the helicals are installed and the brackets are attached to the foundation lifting assemblies, the lift cylinders are installed much the same as push piers. These lift cylinders are routed through a manifold to allow for a synchronized lift. The synchronized lift allows for evenly distributed pressures along the foundation as not to damage the integrity of the structure.
Advantages High ultimate capacities (up to 98,000 lbs.)
Installs with little or no vibration
Soil removal from site unnecessary
Easily load tested to verify capacity
Can be loaded immediately after installation
Minimal effects on landscaping
Installs below unstable or sinking soil
Good for stabilizing lightly loaded structures
Drilled Concrete Piers Drilled concrete piers are constructed in place under your foundation. Special equipment is required to drill a hole into the soil at an angle beneath your foundation. Sometimes a special device is used, after the hole is drilled to enlarge the bottom of the hole (bell bottom pier). It is the wider area at the bottom that carries most of the weight of the foundation it supports. The enlarged area at the bottom resembles a bell when viewed at a side angle.
After drilling, a framework made up of re-bar is then sometimes inserted into the hole. The rebar extends from the top to the bottom providing reinforcement. The hole is then poured full of concrete and allowed to cure. This curing process takes about 14 days and must be complete before work can continue. After drilling the pier the soil that is taken out must be removed or redistributed on the site.
The depth that the pier can reach is limited by the equipment that is used to drill the holes. In some instances the total depth of the hole may not be sufficient to reach beyond the soil that is causing the problem. This will result in the pier not being able to provide proper support. This along with the fact that the pier is installed at an angle also limits the capacity of the pier. Coupled with the fact that the drill can cause moderate to heavy vibrations, the homes ability to withstand these additional forces must be evaluated.
Drilled bell piers rely on skin friction as well as the bell shape for some end bearing support. This amount of concrete adds a significant amount of weight that the original structure was not designed to support. Once these piers are installed and have cured the final step is lifting. Many times these types of piers are used in conjunction with car (bottle) jacks. This type of lifting system is ill advised. Bottle jacks put all of their pressure on a very limited surface of the footing which can cause further problems with the foundation.
• Greatest impact on areas near installation
• Does not provide support directly beneath the foundation
• Long installation times
• Use of bottle jacks to lift
Pressed Concrete Piers
Pressed concrete piers also know as segmented piles, pressed piles or concrete cylinders are made up concrete segments (concrete cylinders) that are pressed into the soil beneath the foundation. These segments are generally only one foot in length and 4-6 inches in diameter. Each cylinder is pressed on the top of the previous cylinder until the structure starts moving upward. The installation of the cylinders is done with a car (bottle) jack. Sometimes a cable is routed down the center of the cylinders to “strengthen and align the piling”. In short, cables are flexible; their only use is to prevent the segmented piles from falling off one another and determining the installed depth.
There are many variations of this type of piling system and there is no universal system or standard for which each cylinder is cast. Simply put the cylinders may not be as strong as the footing they are supposed to support. In addition, during lift, bottle jacks can lift unevenly, causing fractures in the foundation.
Installation is very quick and very little equipment is needed to install. The blunt end of the concrete cylinder often prevents reaching a load bearing stratum. Imagine taking a brick into your front yard, standing it on edge, and then pressing it into the soil. As you can imagine it would take a tremendous amount of pressure, this pressure is applied to your footing. Now stack another brick on top of the previous one and start pushing again, I think you get the idea. It makes for an inexpensive piling system, but with widely varied results.
Pressed concrete piers are probably the cheapest of all pier types. That is why it is the most commonly used method of foundation repair. In some areas, they account for more foundation repairs than all other methods combined. They are also why the foundation repair industry has a “black eye” in the mind of the average homeowner.
• Relatively quick to install
• Cost effective
• Installation can be messy
• Usually not installed below active soils
• Not field load tested
• Uses bottle jacks to install and lift
• Variable strength (or weakness)
Slab Jacking or Mud Jacking
This method does not require piers of any sort. For foundation applications it should be used along with one of the other foundation repair methods. Its best application is for exterior slabs like driveways and sidewalks.
Mud jacking raises the concrete slab by injecting different materials beneath the slab, usually a special mixture of grout via a hole drilled through the slab, under high pressure, effectively floating it back into place. Slab Jacking works well for areas like driveways, patios and walkways. It should not be used as the primary method of raising a foundation. It can be used to fill voids after a foundation has been raised using other methods, but be forewarned that it can cause additional damage if it is used in the wrong circumstance.
If mud jacking is used in soils that have consolidated or shrunk due to drought, extreme damage can occur when the soils are hydrated. There will be no where for the soils to expand to their original volume. In this case, the foundation would be pushed beyond its original level and possibly causing severe damage. While slab jacking can be a useful method of filling voids, care must be taken to maintain a constant moisture level.
• Very little if any impact on landscaping
• Good solution for exterior slabs
• Extremely dangerous
• Soil moisture must be controlled
• May cause additional foundation damage
Helical Tie Backs
Helical tie backs are used to anchor or support bowing, leaning or unsound basement walls. The first step in their installation is to remove the soils adjacent to the basement walls.
A small hole is then drilled into the wall to allow the helical shaft to be inserted. As with vertical applications, the helical screw anchor is installed using a rotary hydraulic torque motor. Upon reaching a suitable bearing depth a wall plate is installed on the interior surface of the wall and then connected via a solid threaded bar. This plate is then tightened against the helical anchor which draws the wall back to its original location. The soils are then back filled against the wall. Generally an aggregate is used for backfilling to avoid lateral pressure being reapplied to the basement wall.
While tie backs do nothing to support settling foundations, when used in conjunction other foundation repair methods, they are a very effective method to support damaged walls. Due to their structural nature square shaft helical screw anchors are ideally suited for these tension applications. As with all helical anchors a foundation engineer is needed to determine loads, soil depth and configuration.
• Quickly installed
• Installs with little or no vibration
• Easily load tested to verify capacity
• Can be loaded immediately after installation
• Installs below unstable or sinking soil
• Engineered solution
• Adjustable length to reach stable soils
• Perimeter soils must be removed
Earth Plate Anchors or Wall Anchors
Plate anchors are simple un-engineered devices to permanently stabilize basement and retaining walls. Known throughout the industry as wall plates, soil anchors, cleats, dead man anchors or cross plate anchors, these anchors provide an opportunity to straighten your basement wall over time. Minimal soil disturbance is necessary for the installation of these anchors which make them a very popular choice for homeowners and property managers alike.
They consist of a heavy-duty galvanized steel wall plate, galvanized all thread rods and a heavy duty galvanized cross shaped earth anchor cleat. The cleat anchors and wall plates have stiffening ribs embossed into them for added strength. The earth anchors are embedded in a firm stable soil mass away from the foundation wall. The threaded bar is then driven to this cleat and through the inside wall plate. This rod is then slowly tightened to stabilize or move your basement wall back to its original position. This process of providing supplemental lateral force to help stabilize bowed and cracked walls is done over time just like your basement wall moved in the first place, over time.
The plate anchor system works on most any type of basement or retaining wall – poured concrete, block or stone. The installation is not intrusive and can be done very quickly. While it is not a generally an engineered solution, it works very well as long as a few precautions are taken. First the wall plates must be positioned correctly to supply support for the effected areas. The earth anchor must be placed in a solid soil mass beyond any previous excavations. Lastly, the homeowner must monitor the tightness of the system monthly and apply additional torque as necessary.
• Quickly installed
• nstalls with little or no vibration
• Minimal landscaping disturbance
• Adjustable length to reach stable soils