Negative skin friction is a type of soil-structure interaction problem that can occur in deep foundation structures, such as piles or drilled shafts. It occurs when the soil surrounding the foundation element undergoes consolidation or settlement, causing the foundation to experience a downward load. The resulting shear forces cause frictional resistance between the soil and the foundation, which can lead to a negative load that opposes the original applied load. This negative load is known as negative skin friction.
The causes of negative skin friction can vary, but typically occur when there is a difference in settlement between the foundation and the surrounding soil. This difference in settlement can be caused by changes in soil properties, groundwater levels, or other factors that affect the soil's ability to support the foundation. Negative skin friction is most commonly seen in soft, compressible soils such as clays, silts, and peats.
The negative skin friction force is determined by multiplying the coefficient of friction between the foundation and the surrounding soil with the magnitude of the downward settlement or consolidation. The magnitude of negative skin friction depends on the time rate of settlement, the magnitude of the applied load, and the stiffness of the foundation.
Negative skin friction can have serious implications for the design and performance of deep foundation structures. It can cause significant reductions in the capacity of the foundation to support the applied loads, resulting in excessive settlement or even structural failure. In order to prevent or mitigate negative skin friction, various design and construction techniques can be used, such as increasing the depth of the foundation, reducing the stiffness of the foundation, or using soil stabilization methods.
In summary, negative skin friction is a type of soil-structure interaction problem that can occur in deep foundation structures due to differential settlement between the foundation and surrounding soil. It can cause significant reductions in the capacity of the foundation to support the applied loads, and therefore should be carefully considered and appropriately addressed during the design and construction phases of a project.
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