Why Does a Foundation Settle?
More About Settlement Repair
Pinpointing the Settlement Issues with Your Foundation and Implementing Permanent Solutions
It is rare that foundation problems are the fault of the design of the structure itself. Most of the time, these problems arise from conditions UNDER the building…the changes that occur in the soils that support the foundation and therefore, the entire structure.
The list below briefly outlines some of the more common causes of foundation settlement:
Weak Load-Bearing Soils
Sometimes, the soil beneath a foundation is simply not able to support the weight or pressure exerted by a structure’s foundation. When this happens, the footings can sink into soft soils, much like a person standing in the mud sinks into sand or soft, wet clay. Commercial design experts often order footings constructed to distribute the weight evenly over the weak soils, reducing the potential for foundation settlement. However, in most cases the settlement problems caused by weak load-bearing soils occur in residential construction, where footings are designed to follow general guidelines and are not modified to fit site-specific soil information.
Faulty Soil Compaction
The use of fill soils is typical in the construction of both commercial and residential subdivisions.
In most cases, before a foundation can be erected on an open lot, hilltops or rises are shaved down and depressions or valleys are filled in order to create surfaces suitable for building. Very, very few lots are level and even from the beginning! When fill soils are placed and compacted properly, they provide sufficient support for foundations. However, when not handled properly, imported fill soils can shift or settle under the weight of the foundation, resulting in damage to the structure.
Moisture Content Changes
Changes in the dryness or moistness within the soil surrounding the foundation can result in damage to the structure. The saturation of foundation soils, caused by an excess of moisture, often leads to the softening and weakening of various types of soils, including clays and silts. When overly moist, the soil is unable to support the weight of the structure, resulting in the settlement of the foundation. Various situations can lead to increased moisture within foundation soil, including poor surface drainage around the structure, water line or plumbing leaks or a raised groundwater table caused by heavy rains, flooding or an excess of winter snow melt.
Loss of moisture can affect soil with high clay content, causing it to shrink. When clay soils shrink or contract, a general decrease in soil volume is the result. The decreased soil volume can lead to settlement damage, as the reduced volume of soil has less ability to support the structure. The drying of foundation soils is often caused by long-term drought-like conditions, mature trees and vegetation (as mentioned below) and/or leaking subfloor heating, ventilation, and air conditioning (HVAC) systems.
Mature Trees and Vegetation
If mature trees, bushes and other vegetation are in close proximity to a home or building, they can be a common cause of foundation settlement. As plant life matures, the demand for water grows along with it! The root systems of the vegetation expand as the plants grow. Their increased need for water and the extended reach of these root systems force the plants to draw moisture from the soil beneath the foundation. As a rule of thumb, the diameter of the root system of a tree is usually at least as large as the tree’s canopy.
As we mentioned earlier, clay-rich soils will shrink as they lose moisture. This can result in the settlement of structures atop these root systems. It may take decades for the plants to cause these types of settlement problems, as this time frame coincides with the maturation and growth of the trees and vegetation. Deep, basement level foundations are often less affected by tree root dehydration than foundations closer to the soil surface.
Soil consolidation is a concern when the weight of fresh fill soils or of a new structure compresses lower, weak clay soil. This extra load squeezes the water out of clay soil, allowing the individual soil particles to become more densely spaced. Soil consolidation causes a downward movement or settling of overlying structures. Over time, settlement can continue. It may take weeks, months, or years for soil consolidation to be considered “complete.” As the process continues, the foundation will display additional downward movement – often at an uneven rate. This situation often leads to cracking foundations and structural damage.
Call on Us to Solve Your Foundation Settlement Problems!
At BL Bennett Structural Solutions, we excel in providing both homeowners and commercial customers with permanent, guaranteed solutions to settling foundations and structures. We always provided a professional inspection and consultation for your affected building at no cost to you. Contact us by phone or e-mail today!