How does the presence of expansive soils beneath a pavement structure influence maintenance and rehabilitation decisions?

Expansive soils are soils that significantly change in volume due to variations in moisture content; they swell when wet and shrink when dry. The presence of expansive soils beneath a pavement structure creates several challenges that influence maintenance and rehabilitation decisions. The repeated swelling and shrinking of the soil can cause the pavement to heave, crack, and distort, leading to premature failure. This movement is not uniform, creating differential heaving which is particularly damaging. Therefore, traditional maintenance techniques like patching and overlays may provide only temporary relief because the underlying soil movement will continue to damage the pavement. Several strategies are used to mitigate the effects of expansive soils. Soil stabilization involves modifying the soil to reduce its swelling potential. This can be achieved through techniques like lime stabilization, cement stabilization, or chemical stabilization. These methods alter the soil's composition to make it less susceptible to moisture changes. Another approach is to improve drainage to minimize moisture fluctuations in the soil. This can involve installing subsurface drains, improving surface drainage, or using impermeable membranes to prevent water from entering the soil. A common solution is to increase the thickness of the pavement structure, especially the base and subbase layers. This provides a buffer between the expansive soil and the pavement surface, reducing the stress caused by soil movement. Replacing the expansive soil with a non-expansive material is another option, although it can be expensive. Pre-wetting the expansive soil before pavement construction can also help to reduce future swelling. Regular monitoring of pavement condition is essential to detect early signs of distress caused by expansive soils. This allows for timely intervention and prevents more extensive damage. The chosen maintenance and rehabilitation strategy will depend on the severity of the expansive soil problem, the traffic loading, and the available budget. It's often a combination of strategies to effectively address the issue.