Some visual indicators of foundation settlement:
- Noticeable slopes in concrete floor slabs or floor framing. Typically sloped down towards the exterior walls.
- Diagonal cracks in foundation walls, wider than 1/8″.
- Cracks in foundation walls which are not uniform in width.
- Diagonal cracks in the exterior masonry.
- Outward bowing of shallow foundation walls.
There are four common causes of foundation settlement in the Chicago area.
- Buildings constructed on fill materials which were not properly compacted.
- Organic material, such as a layer of peat, present under the foundations.
- Drying and compaction of the soil, also known as soil desiccation, under the foundations.
- Slope instability. Less common in Chicago area as the land is relatively flat.
Not every foundation settlement problem requires stabilization. There are several factors to consider before proceeding with foundation stabilization and lifting. The magnitude of movement, the distress being caused to the building, the age of the building, the cost of stabilizing the foundations, the destruction to the area around the building, and destruction to other structures adjacent to the area to be stabilized.
Foundation stabilization and lifting is typically done by one of two methods. The first method is to hydraulically push a steel pile into the ground using the weight of the building as a reaction force. The second method utilizes a steel shaft with one or more “threads” or helical shaped steel plates at the beginning of the anchor which allow the steel shaft to be turned or screwed into the ground. This anchor relies on the “threads” bearing on stable and adequate soils to support the building loads. Both methods of foundation stabilization and lifting are commonly referred to as piering.
It has been our experience that helical or screw type piers are effective only when the pier can be driven straight into the ground, for example to support a new basement floor constructed as a steel reinforced concrete slab or a new building which is starting with open ground and new foundations. Unfortunately, because of the equipment required to install a helical or screw type pier, it is very difficult to drive the pier straight into the ground next to a foundation wall and the pier ends up going into the ground at an angle. This condition leads to a bending stress being induced into the pier shaft which can lead to failure.
Push or hydraulically driven piers can be driven straight into the ground very close to the foundation wall and are therefore more effective at supporting the foundation wall and the building loads on them. Also the capacities of push type piers can far exceed that of helical or screw type piers.
Typically the exterior walls of industrial and commercial buildings have relatively high dead loads from the wall and roof system. To prevent excessive rotation and bending of the piers these walls are typically piered from the interior and exterior to balance the loading on the piers and prevent excessive rotational forces on the piers.
We have designed and developed our own push pier system which we manufacture. The technology used in our design can be varied to increase pier capacities to fit almost any application, including heavy multi- story commercial buildings.
You may require an engineering consultation if you are not sure that your building has a foundation settlement problem which requires repair. A Structural Engineering investigation of your building to determine if foundation stabilization is required typically costs $500 to $800. Providing a written estimate for stabilizing the foundations is included, assuming the building is not a complicated structure or the settlement problem is not extensive. The estimate includes calculating the building loads down to the foundation walls and making sure that the foundation walls have the capacity to carry the building loads from pier to pier. Our objective is to minimize the number of piers required to support the building loads without causing a failure of the foundation wall.
If you know that you have a foundation settlement problem which requires stabilization we can, in most situations, provide an estimate for doing repair work free of charge.
Example 1: Heavy Precast Building
This is a precast concrete building which was experiencing significant differential settlement along the back and side walls. The exterior walls and roof were all constructed with precast concrete making the building very heavy.
Example 2: Under Pinning Metal Building With Partial Height Concrete Block Wall.
A deep excavation at the interior of this building, adjacent to the outside wall, was required to install a large tank. This excavation was much deeper than the foundations so under pinning with piers was required to support and maintain stability of the building next to the excavation.