Causes and Signs of Failed Foundations

Foundation problems can be caused by both homeowners and mother nature. No matter if you've lived in the same home for years or have purchased a newer home, it is good to know the causes and signs of a failing foundation. Unfortunately, mother nature can cause foundations to fail and a homeowner can't do much about it. Knowing the signs and getting your foundation fixed by a professional foundation contractor early can potentially save you thousands of dollars. Foundation problems don't go away on their own, they only get worse.

Causes of Foundation Problems that Lead to Failure

foundation repairMost foundation problems are caused by the soil surrounding a home. Throughout the year the soil expands and contracts from moisture and temperature levels. Foundations fail when there is too much water or not enough. Sections of the soil can have different moisture levels causing the soil to swell and shrink at various locations. Some sections of the soil can become much drier or wetter than other parts causing stress on your home's foundation. These inconsistencies in the soil generally result from overloading, poor water management, faulty compaction, an abundance of organic materials, and erosion.

Transpiration The soil dehydrates because of tree roots beneath the home. The soil shrinks because of this loss of moisture. The soil shrinkage causes homes to settle. 

Plumbing Leaks Water can seep into the soil from leaky pipes. This causes too much water in the soil and can contribute to unneeded stress on the walls of the home's foundation.

Drainage Poor drainage both on the exterior and interior of your home's foundation can cause excess moisture to build up in the soil. This may cause soil heaving. 

Poor Building Site Preparation Commonly on building sites soil is removed from part of a building and piled on other soil. The soil needs proper stabilization before the structure is built; otherwise, the soil may move below the structure.

Common Ways Homeowners Cause Foundation Failure

  • water and rainOverwatering Lawns - this is a common way to create the areas of wet and dry soil
  • Planting Too Close To House - It is important to keep plants a safe distance from the foundation, usually more than 5 feet. Roots can cause soil moisture differences and can also grow into the home's foundation.
  • Swimming Pools - seepage from a swimming pool can leak into the soil causing increased pressure on the foundation.
  • Gutters and Downspouts - gutters and downspouts not installed correctly can lead water directly down to your foundation. Be sure to fix leaky gutters and draw water away from the home.
  • Interior Remodeling - large changes to your home's structure can put pressure on your foundation. Hire a professional contractor to ensure the foundation can handle the structural changes.

A foundation's movement and cracking may result from a wide range of hidden factors, which may include:

  • Swelling or Shrinking of clays caused by changes in moisture content
  • Compression of the ground as a result of the applied foundation loads
  • Soil softening
  • Frost heave
  • Improper backfilling of the foundation
  • Variation in groundwater levels
  • Erosion or undermining of the foundation
  • Vibration from nearby construction
  • Hydrostatic Pressure on the foundation

Inadequate design of basement walls, footings, and slabs traditionally account for 75 to 85 percent of all problems in homes built upon expansive clay soils. These failures are generally divided between two broad classes of failure – lateral pressure and differential settlement. Both classes of failure generally have few primary causative factors.

Lateral pressures on basement walls have four likely sources:

  • Pressure from soil weights
  • Pressure from soil swelling
  • Hydrostatic pressure
  • Pressure from frost

foundation problemsIt is not difficult to identify lateral pressure, but accurately quantifying the source is very difficult and should only be handled by a qualified engineer. The inward bowing of a basement or retaining wall is the simplest indication of lateral pressure. The bowing generally occurs when the external forces exceed the wall strength. The maximum bowing will often occur near the center of the wall because the adjoining perpendicular walls provide support in the corners. If bowing becomes severe, these walls can collapse inward.

Cracking can occur when the lateral pressure exceeds the strength of the concrete or block wall. The most common crack pattern begins in the corners and moves up or down at 45-degree angles in concrete walls. For block walls, the cracks move along the mortar joints in a stair-step pattern. Often these cracks end at a long horizontal fracture that parallels the basement floor.

Lateral pressures may affect the overall integrity of a house. Severe structural damage results in a visible opening between the top of the basement wall and the structure. Since water is one of the main causes of these cracks, water infiltration becomes significant in the largest of the cracks. Filling these cracks with epoxy, without solving the water problem, only moves the lateral pressure to another section of the wall.

The difference of the outside ground level and the basement floor creates a mass of soil that must be retained thus causing a lateral pressure. Picture a walkout basement or a tall retaining wall. The pressure of soil weight is typically considered during the design of an engineered wall using theoretical earth pressures.

Soils with heavy clay content undergo a change in volume when the moisture content of the soil changes. When expansive clays are placed against basement walls, the swelling of these soils can induce lateral pressures not accounted for in the original design. Cyclic shrink/swell can also reduce the shear strength of the backfill and thus increase the lateral pressures. The solution to this problem can be as easy as replacing clay backfill with gravel or other non-swelling material. When used in conjunction with a footing drain, gravel will prevent increased lateral pressure.

Hydrostatic pressure is pressure exerted by a fluid due to its weight. Hydrostatic pressure against a basement wall develops when water fills voids or “ponds” within backfill immediately adjacent to the wall. This water buildup can cause dripping, seepage, dampness, or efflorescence (salt residual). Leakage during heavy rains or poorly designed/maintained drainage increase hydrostatic pressure. Like soil swell, hydrostatic pressure is not typically considered during design and construction of basement walls.

waterproofing your homeWater that accumulates in backfill and then becomes frozen may cause a large amount of lateral pressure on basement walls. Severe damage can result from frost causing lateral pressures much greater than even hydrostatic pressure. The expansive natures of water crystals have been known to create catastrophic structural damage.

Backfill that is heavily laden with clay, present long-term lateral soil pressure problems. Their cohesive nature makes it practically impossible to re-compact them to a uniform moisture content and density. Clay backfills require significantly stronger basement walls to withstand the larger horizontal pressures. The obvious solution is to backfill with non-cohesive aggregate with proper drainage.

A structural settlement is characterized as either total and /or differential settlement. The total settlement is a complete structure downward movement. Differential settlement is the difference in vertical movement between various locations causing structure distortion. Generally, total settlement is not a critical factor as long as it is uniform. Utility connections are affected to the greatest degree by the total settlement. Even relatively small differential settlements can cause cracks in floor slabs, brick walls, and drywall.

Some amount of settlement can be tolerated in most homes provided it is within specified limits. Small amounts of settlements are anticipated in most design work. When homes experience excessive settlement special procedures must be employed to stop or limit the amount of settlement. These special procedures usually employ the use of steel piers or helical anchors.

 

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