Progressive compression describes which scenario?

• A. Planar shear that required at least one tap to cross column and block doesn't slide easily
• B. Sudden crack in column and noticeable collapse
• C. Thin planar crack crosses column
• D. Nonplanar fracture of noticeable thickness followed by compression of layer with noticeable taps

Answer: (D)

Progressive compression is a gradual, nonplanar fracture process that develops with noticeable thickness as load increases, and it is followed by compression of the surrounding layer that may produce visible taps as the crack and contact zones interact. The scenario described matches this pattern: you have a fracture that is not simply a flat, thin crack, but a thicker, nonplanar break, and after that fracture forms, the adjacent layer undergoes compression evidenced by the taps. This captures the slow, progressive nature of the failure, rather than an abrupt, planar crack or sudden collapse.

The other descriptions fit quicker, more abrupt events or simpler crack geometries that do not embody the slow, nonplanar progression and the subsequent layer compression with taps that define progressive compression.