What phenomenon occurs due to a sudden large decrease in shearing resistance of cohesionless soil?

The phenomenon that occurs due to a sudden large decrease in shearing resistance of cohesionless soil is liquefaction. Liquefaction is a process where saturated or partially saturated granular soils lose strength and stiffness in response to applied stress, often during an earthquake or other sudden loading conditions.

During liquefaction, the pore water pressure in the soil increases, which can lead to a loss of effective stress—the stress that contributes to soil strength. As a result, the soil behaves more like a liquid than a solid. This phenomenon is particularly prevalent in loose, sandy soils that are saturated.

Understanding liquefaction is crucial for geotechnical engineers and geologists, especially in seismically active regions where the potential for earthquake-induced ground failure can have disastrous consequences, including building collapse and ground displacement.

The other options pertain to different geologic or engineering phenomena. Hydrocompaction involves the densification of soil typically due to moisture infiltration, lateral spread refers to the horizontal movement of soil or other materials on a slope, often associated with liquefaction but different in context, and microseism refers to small, undetectable vibrations of the ground. Each of these has distinct characteristics and mechanisms separate from the rapid loss of shearing resistance seen in