Most people have encountered or heard of structures that have experienced some kind of movement and foundation damage. If the movement and damage are severe enough, foundation repairs may be needed, and those repairs can be costly and disruptive.
While the need for foundation repairs can be associated with a variety of causes, this article will focus on the more common types of foundation repair methods rather than those causes.
The most common repair method to address foundation movement is underpinning, or providing new support members for the foundation system. Underpinning frequently involves the installation of slender members into the ground beneath a foundation to a depth that will provide adequate support for the structure. Underpinning is typically performed to address non-uniform settlement or heave of a structure. Some of the frequently used systems for underpinning that are utilized include the following:
A helical pile is defined in the 2015 International Building Code (IBC) as a “Manufactured steel deep foundation element consisting of a central shaft and one or more helical bearing plates. A helical pile is installed by rotating it into the ground. Each helical bearing plate is formed into a screw thread with a uniform defined pitch.”
A micropile is defined in the 2015 IBC as “…a bored grouted-in-place deep foundation element that develops its load-carrying capacity by means of a bond zone in soil, bedrock or a combination of soil and bedrock.”
A steel push pier consists of steel tubing that is pushed into the ground with a hydraulic ram. The steel tubing is advanced to refusal or appropriate load-bearing strata. The weight of the structure being underpinned is commonly used as resistance as the steel tubing is pushed into the ground.
Helical piles and steel push piers have the added advantage of, in-effect, being load tested during their installation, as the torque needed to install the helical piles and the force needed to install the steel push piers is measured and can be converted to a load capacity. The load testing of micropiles has to be performed after their installation is complete; however, an advantage of micropiles is that the installed depth (and therefore the cost as well) is, in almost all cases, known prior to the installation process commencing.
When underpinning of a foundation is performed, the loads of the structure are most often transferred to the underpinning member by means of a steel bracket that is connected to both the existing foundation element and the top of the underpinning member. The steel bracket and underpinning member also allow in most cases for an attempt to be made to improve the level condition of the subject structure.
Underpinning of a foundation can be done if the structure has experienced settlement or heave. In instances where heave has occurred, typically creating a void space, or re-establishing a void space, beneath the original foundation is incorporated in the repair procedure, in order to isolate the underside of original foundation elements from the expansive soil.
At sites where settlement has occurred, compaction grouting or expanding urethane injection may be suitable alternatives to underpinning. Either a concrete slurry (soil, cement and water – sometimes referred to as “soilcrete”) is pumped into the ground beneath the foundation, or expanding urethane (and structural resin and hardener) is injected. These materials can be effective in consolidating and stabilizing soil, thereby improving the load-bearing characteristics of the soil.
The type of foundation repair method to be utilized for an individual structure is normally recommended by the project geotechnical and/or structural engineer. The soil conditions or other situations at a particular site may hinder the installation of a particular type of underpinning member, or may be such that a specific type of repair is not suitable and is unlikely to perform in a satisfactory manner.
Advantages of underpinning, compaction grouting, and expanding urethane injection, over demolishing and re-constructing damaged portions of the foundation system include lower costs, lesser disturbance, the aesthetics of the structure usually not being adversely affected, along with the fact that these repair methods can be implemented in areas with limited access including interiors.
At Western Engineering & Research Corporation (WERC) we have licensed Professional Engineers (PE) with decades of experience in conducting thorough forensic investigations in order to provide sound and substantiated opinions, and repair recommendations. If you are in need of structural engineering services related to foundation repairs, call WERC at (800) 303-9800; we are available 24/7.