What type of material may cause sand to shrink under high head loss and create cracks?

The correct answer is gelatinous material. Gelatinous substances are often associated with high water content and can create a slippery, cohesive mass that holds water. When high head loss occurs, such as in situations where there is rapid flow or extreme pressure differences, the gel-like consistency can lead to issues like shrinkage and cracking in sand.

As the water is drawn away from the surrounding material, the gelatinous material loses its structure and can exacerbate the shrinking process in adjacent sandy soils. This can create voids or cracks through which water can move more freely, potentially causing further instability in the sand.

The other materials listed, while they can affect soil behavior in different ways, do not lead to the same gelatinous effect that causes cracks in sand under high head loss conditions. Clay, for example, can swell and retain water but typically does not create the same shrinkage issues, while granular materials are more stable and do not form cohesive gels. Organic materials can decompose but also do not lead to the characteristic shrinkage and cracking seen with gelatinous substances.