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Soil mechanics

Before a determination is made whether or not repairs are necessary, it is of utmost importance to have an understanding of the geological content of the existing soils beneath the foundation in question.

Soil composition can radically vary from one lot to another for a plethora of reasons, so even if a repair is warranted, the solution could be an entirely different pier system, drainage solution, soil injection, root barrier installation, or an excavation and disable project could be the correct intervention.

Often times, simple corrections to grading, water mitigation with gutters or redirected downspouts, or even a repaired plumbing leak or redirected a/c drip line is all that is necessary to correct movement in the foundation.

Having a basic understanding of both physics and applied mechanics is of paramount importance when assessing potential foundation movement, since there should be a distinct correlation with the signs of foundation movement with both the soil composition and potential causation of expansion or contraction depending on the soil plasticity.

Depending on the plasticity index, the amount of shrinking or swelling will vary, as well as the permeability, compressibility, or shear strength in the soils.

For these reasons alone, this information is essential in identifying the right solution for long term stability.

Plasticity index, also known as Atterberg limits, is the basic measure of the critical water contents of soil: shrinkage limit, plastic limit, and liquid limit. 

 

 “Because water serves as the catalyst to the expansion of the clay or silty soil, if an equilibrium does not exist around a foundation that has a PI above 24, structural failure is highly probable.”

Soil injections, drainage, and a complete underpinning of a foundation lifted beyond the total PVR, or potential vertical rise, can be used to mitigate further movement, but is often misinterpreted as settlement or soil consolidation where no problem exists at all.

Consolidation is a process by which soils decrease in volume. It occurs when stress is applied to a soil that causes the soil particles to pack together more tightly, therefore reducing volume. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil, which can cause settlement of the foundation. 

 

 “When stress is removed from a consolidated soil, the soil will rebound, drawing water back into the pores and regaining some of the volume it had lost in the consolidation process. ”

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