Liquefaction indicators in geotechnical engineering and their mitigations: which combination is correct?

• A. Indicators include sand boils and lateral spreading; mitigations involve deep foundations only.
• B. Indicators include sudden settlement only; mitigations involve relocation of structures.
• C. Indicators include sand boils, lateral spreading, and sudden settlement; mitigations include soil improvement, drainage, and deep foundations.
• D. Mitigation relies solely on early warning systems.

Answer: (C)

Liquefaction occurs when saturated, loose sands lose strength during strong shaking, leading to ground deformations. The key indicators to look for are sand boils (water and sediment erupting at the surface from pressurized pore water), lateral spreading (horizontal ground movement away from loads or along slopes), and sudden settlement (rapid loss of bearing capacity causing uneven settlement). These indicators reflect the sudden rise in pore water pressure and loss of shear strength that characterize liquefaction.

Mitigations focus on reducing pore pressure and increasing ground resistance. Soil improvement methods densify and stabilize the near-surface sands so they resist liquefaction. Drainage improvements help dissipate pore water pressure during shaking, limiting the fluidizing effect. Deep foundations transfer loads to deeper, more stable layers, bypassing the weak, liquefiable stratum and reducing susceptibility to failure.

That combination fits well because it covers both the observable signs of liquefaction and a set of practical, widely used strategies to prevent or lessen its impact. The other options miss important indicators or mitigation approaches—for example, relying only on deep foundations, or focusing on a single indicator and ignoring drainage or soil improvement, or suggesting that mitigation is only about early warning systems.