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Foundation heave is the movement of expansive soil due to changes in its moisture content. The foundation heave occurs in various patterns like doming, edge, cyclic, and lateral movement.
Differential movement of expansive soil is more damaging than a uniform heave. It mostly affects lightly loaded structures like one or two-storey structures, highways, retaining walls, canal linings, and reservoir linings.
Building damage due to heave occurs within a few months after construction and may develop over about five years, or it may not be visible till some changes occur in the soil moisture.
Contents:
What are Patterns of Foundation Heave?
Doming or Edge Down Heave
Foundation heave is generally erratic but can occur with an upward, long-term, dome-shaped movement that develops over several years. The greatest heave occurs toward the center of the structure.
A doming heave causes the external walls in the superstructure to lean outward, initiating horizontal, vertical, and diagonal fractures with larger cracks near the top.
The roof of a building restrains the rotation due to differential vertical movement, causing additional horizontal fractures near the roofline at the top of the wall.
A dry, hot, semi-arid climate and deep water table can be more conducive to severe and progressive foundation soil heaves if water becomes available.
Cyclic Heave
A cyclic expansion-contraction associated with drainage, frequency, and amount of rainfall and evapotranspiration may be superimposed on a long-term heave close to the perimeter of the structure.
Localized heave may occur around the ponded area or water leaks. Evapotranspiration is the moisture evaporation from the ground surface and the transpiration of moisture from heavy vegetation into the atmosphere.
Downwarping from soil shrinkage can develop underneath the perimeter of the building during dry and hot periods or from the desiccating influence of trees and vegetation close to the structure. These edge effects may extend inward around 2.4 to 3 m and become less effective in a well-drained land.
Heavy rain periods may cause ponding adjacent to the structure with edge lift and reversal of down warping.
Edge Heave
Edge or dish-shaped heaving of portions of the perimeter of a building may be noticed relatively soon after the construction, especially in semi-arid climates on construction sites with preconstruction vegetation and a lack of topographic relief.
The removal of vegetation leads to the increase of moisture in the soil, whereas the absence of topographic relief leads to ponding.
Edge heave may also occur beneath foundations due to consolidation, drying out of surface soil from heat sources, or sometimes, lowering of the water table. Lowering the level of the water table in uniform soil beneath uniformly loaded structures may not contribute to differential heave.
However, buildings on a deep foundation, like drilled shafts with slab-on-grade, can be severely affected by water table variations or soil moisture changes if the slab is not isolated from perimeter grade beams and if the internal walls and equipment are not designed to accommodate slab movement.
Lateral Movement
Lateral movement can affect the integrity of the structure. The lateral thrust of expansive soil with horizontal force up to the passive earth pressure can lead to the bulging and cracking of basement walls.
Basement and supporting walls do not tolerate the same movement as a cantilever retaining wall, so they have to be designed to a higher degree of stability.
Foundations and walls built on slopes greater than 5 degrees may suffer damage due to downhill soil creep of cohesive expansive soils. Downhill soil creep can also generate shear force on shaft foundations. The depth of creep may range from a few inches to several feet.
FAQs
Foundation heave is the movement of expansive soil due to changes in its moisture content.
The foundation heave occurs in various patterns like doming, edge, cyclic, and lateral movement.
Lightly loaded structures like one or two-storey structures, highways, retaining walls, canal linings, and reservoir linings are mostly affected by foundation heave because their loads do not suppress the expansive soil movement.
A Doming heave causes the external walls in the superstructure to lean outward, initiating horizontal, vertical, and diagonal fractures with larger cracks near the top. The roof of a building restrains the rotation due to differential vertical movement causing additional horizontal fractures near the roofline at the top of the wall.
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What are the signs of foundation heave?
