Under what conditions is liquefaction most likely to occur?

Liquefaction is a phenomenon where saturated sandy soils lose their strength and stiffness in response to applied stress, often due to seismic activity or other dynamic loads. The conditions that facilitate liquefaction predominantly include the saturation of the soil and the presence of granular material such as sand.

Choosing lightly loaded sand layers that are situated 15-20 meters below the surface indicates that these layers are likely to be fully saturated. The depth provides a buffer against immediate surface load impacts, allowing for a build-up of pore water pressure during an event, such as an earthquake. When the p-wave stresses reach a threshold, the pore pressure can increase sufficiently to cause the effective stress to drop, leading to a rapid loss of strength and the potential for liquefaction.

The other conditions presented in the remaining options do not align with the critical characteristics needed for liquefaction. For example, saturated shallow clay layers with heavy loads would likely not experience liquefaction since clay tends to exhibit plastic behavior and shear strength persistence when loaded. Similarly, dry sandy soils under high pressures are not conducive to liquefaction because the presence of water in the pores is essential for the phenomenon to occur. Lastly, uniform gravel particles in saturated conditions are less susceptible to liquefaction due to