The problem lies in what lies below the foundation or concrete. The soil is always the problem and depending on which area your house is in, it could be a number of reasons why the soil has failed. In BC, the sediments vary from soft peat to mountain bedrock. The soils react differently over time but the 3 major causes of settlement are: drying and shrinking of the soils, wetting and softening of soil and poorly compacted fill soil.
During prolonged dry periods, the soils around your home may begin to dry. Clay soils shrink considerably when they dry, creating a void between the structure and the soil it’s relying on to support it. When this happens, your foundation settles as well, frequently resulting in structural damage.
Water can pose dangers for your home’s foundation in several ways: Heavy rain and flooding: When clay soils contact water, they retain it and become very soft. Soft soil does not bear loads well, causing heavy objects to sink into it. Poor drainage: If water is allowed to “pool” next to the home due to poor soil grading, clogged gutters or some other factor, soils absorb the water. If soils around the home are clay, they will soften. This can cause the home to sink. Plumbing leaks and broken water lines: Plumbing leaks under or near a home can saturate soils around it, potentially weakening their load-bearing capacity. Often, plumbing leaks push soil out from under the home, creating a void into which a home or building can sink.
When leveling a lot to prepare it for your home’s foundation, builders often use soil from another location to fill hollow or depressed areas. This recently excavated fill soil can be looser and lighter than the dense, hard-packed virgin soils already present. To compensate, builders frequently compact the fill soil thoroughly before placing a foundation. If this compaction is not done, or is done poorly, your home’s weight may cause the soil to compress, leading to foundation settlement issues.