What causes concrete to sink or become uneven?
There are many reasons that can cause your concrete to sink and often times it can be hard to identify some of the problem areas. You will come across it in the form of uneven, cracked, or sunken concrete slabs. You will hear some companies refer to this as slab settlement. What is slab settlement you ask? Well, slab settlement refers to the sinking or movement of a concrete slab when the soil below the slab can no longer support the weight of it. This happens on driveways, patios, sidewalks, pool decks, stairs, garage floors, and foundations around the country.
The Three Main Reasons Your Concrete Is Sinking
When it comes to slab settlement and concrete sinking, changing soil conditions underneath your concrete is generally the main culprit. While there are many reasons that can cause this, there are three main causes.
Soil Washout underneath your concrete slab
Poorly compacted fill soil
Soil moisture content fluctuation
Soil Washout Beneath Concrete Slabs
Water caused by plumbing leaks, erosion, large rainfall, etc. will find its way underneath concrete slabs in your walkways, pool decks, garage and basement floors. As this water moves through the soil beneath your concrete, it can wash away the soil that is supporting the weight of the concrete. As this occurs over time, the amount of soil present underneath the concrete slab will diminish and your slabs will begin to sink due to a lack of support material.
Poorly Compacted Fill Soil
During the construction of a driveway, patio, sidewalk, or foundation, the soil is most often spread out or moved to achieve the desired grade level. If this soil is not properly compacted and a new slab is poured over the top then slab settlement is more likely to occur. The loose soil underneath the slab will compact over time and create empty cavities beneath the slab. Over and with very little support your concrete will crack and fall into the hole beneath. This is most often the cause of cracked concrete and occurs more around the edges and corners of large slabs.
Soil Moisture Content Changes
Cycles of wet and dry weather have a direct effect on the soil underneath your concrete slabs. When soil which large contents of clay get wet, they hold onto the water and expand in size. Later when the soil drys out it begins to shrink. This can leave large sections of your concrete wholly unsupported which can lead to cracking and slab settlement.