Inadequate Drainage and Foundation Movement
Inadequate drainage occurs when the topography is flat, slopes toward the house, or puddles inside closed planters. When irrigation volume is unnecessarily high, or torrential rains occur, this creates ‘ponding’ conditions where water has no escape route (bathtub scenario), or yard drains are blocked due to debris or lack of maintenance.
For many houses, water may have saturated the soil adjacent to the foundation due to inadequate surface drainage during irrigation, past torrential rains, or an excessive use of the hose along the backyard wall. One of the most prevalent scenarios we see is rain gutters draining directly adjacent to the foundation, often into a planter that creates pooling.
Proper drainage is important to keep water away from perimeter foundations to prevent foundation movement. Water percolates through the topsoil to saturate the subgrade soil under the foundation. In such conditions, the soil becomes more compressible. This is known as ‘soil consolidation’. Soil consolidation can occur in most soil types but is far more prevalent in clay-type soil conditions.
The Plasticity Index (PI)
The plasticity index (PI) is a measure of the plasticity of a soil. It is the size of the range of water contents where the soil exhibits plastic properties. The PI is the difference between the liquid limit and the plastic limit ($PI = LL – PL$). The higher the plasticity index, the greater the potential for foundation problems, and the greater need to manage your soil conditions around your home.
Soil Classification
Soil is classified into four types:
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Sandy Soil: Consists of small particles of weathered rock. Sandy soils have very low nutrients and poor water holding capacity. Most desert communities are built on sandy soil and experience little settlement.
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Silty Soil: Made up of rock and other mineral particles smaller than sand and larger than clay. It holds water better than sand. Many homes constructed in lowland valleys near natural water flows or lakes are built upon this type of soil.
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Loamy Soil: A combination of sand, silt, and clay. It is often referred to as agricultural soil as it includes humus. The percentage of clay content will dictate the potential foundation problems.
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Clay (Clayey Soil): The smallest particle amongst the other types of soil. These particles are tightly packed together with very little or no airspace. Clayey soils have a high expansion and contraction rate. Upon moistening, these soils expand; upon drying, they shrink more than they previously expanded, leading to differential settlement.
Do You Know the Signs of Foundation Problems?
Cracks in your foundation or sloping and uneven floors can indicate you have foundation problems. At first, you notice a door won’t open, then a few windows. Cracks start showing up in the corners, and one in the ceiling. The size, location, and shape of the cracks help to determine the severity of the problem.
Signs of Foundation Problems:
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Cracked walls / stuck doors or windows
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Sinking floors / crooked roof
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Leaning chimneys
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Cracked or uneven floors
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Vertical cracks in foundation
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Recent or past sewer replacement