Geotechnical Earthquake Engineering

The Cone Penetration Test (CPT) is an in-situ test that pushes a cone-tipped probe into the ground at a constant rate and measures tip resistance and sleeve friction. It provides continuous, high-resolution soil profiling and is a primary tool for liquefaction assessment and soil characterization.

Cyclic softening is the progressive reduction of soil stiffness and strength under repeated cyclic loading, such as earthquake shaking. It is related to but distinct from liquefaction, and is especially relevant to silts, clays, and dense sands that may not fully liquefy but still degrade under cyclic loading.

Excess pore water pressure is the increase in water pressure within soil pores above the static (hydrostatic) level, generated by cyclic or monotonic loading. Its accumulation under seismic shaking reduces effective stress and can lead to liquefaction, cyclic softening, and ground failure.

Ground improvement is the set of techniques used to modify the engineering properties of soil in place, typically to increase strength, reduce compressibility, or mitigate seismic hazards such as liquefaction. It is a key mitigation strategy for geotechnical earthquake engineering.

Lateral spreading is the horizontal displacement of soil — typically toward a free face such as a riverbank, shoreline, or excavation — caused by liquefaction or cyclic softening during an earthquake. It is a major cause of damage to bridges, pipelines, and waterfront structures.

Liquefaction is the phenomenon in which saturated cohesionless soils lose strength and stiffness during earthquake shaking, temporarily behaving as a liquid. It is a major cause of ground failure, foundation damage, and building collapse in seismic regions worldwide.

Shear wave velocity (Vs) is the speed at which shear waves propagate through soil or rock, determined by the material's shear modulus and density. It is the most fundamental parameter for characterizing the dynamic stiffness of a site and forms the basis for site classification in modern building codes.

Site response analysis is the calculation of how soil deposits modify earthquake ground motion as it propagates from bedrock to the ground surface. It is used to develop site-specific design spectra and to evaluate the effects of local soil conditions on ground shaking.

Soil-structure interaction (SSI) is the mutual influence between a structure and the soil supporting it during dynamic loading. It modifies the structure's effective period, damping, and deformation pattern, and is especially important for stiff, heavy, or embedded structures on soft soil.

The Standard Penetration Test (SPT) is an in-situ field test that measures the resistance of soil to the penetration of a split-spoon sampler driven by a standard hammer. The resulting blow count (N-value) is one of the most widely used indices for soil characterization and liquefaction assessment.