Final answer:
Clay has the greatest chance of shifting during excavation due to its cohesiveness and ability to retain water.
Step-by-step explanation:
The material with the greatest chance of shifting during excavation is clay. Clay is a type of sedimentary rock that is composed of fine particles of silt and has a high plasticity when water is added. Its cohesiveness and ability to retain water make it more prone to shifting and movement compared to other materials such as fractured rock, sand, and stone.