Seismic velocities, specifically primary (P-wave) and shear (S-wave) velocities, are fundamental parameters in both geophysical and geotechnical investigations. Understanding these velocities and their relationship to geotechnical properties is crucial for site characterization, and hazard assessment.
P-wave velocities are typically measured using seismic
refraction tomography (SRT) method; while S-wave velocity measured using Multi
Channel Analysis of Surfaces Wave (MASW) method. Those methods involve
generating seismic waves and recording their travel times to determine velocity
profiles. We are using DAQ LINK-III for field data acquisition and processing
with Rayfract and Seisimager software to produce Vp and Vs profile.
The following section showing the profile of Vp of the study along the taxiway of the APT Pranoto airport in East Kalimantan.
Seismic velocities provide indirect measurements of
subsurface properties and are closely linked to geotechnical parameters such as
density, porosity, and mechanical moduli. The relationships between seismic
velocities and these properties enable the estimation of geotechnical
characteristics. The following table showing the empirical correlation between Seismic Velocity and Geotechnical Properties (Sarkar, et all. 2021).
Density and Porosity
Both P-wave and S-wave velocities are affected by the
density (ρ) and porosity of the material. Generally, higher density and
lower porosity result in higher seismic velocities.
Mechanical Moduli
Seismic velocities are directly related to mechanical moduli
(bulk modulus and shear modulus). These
moduli describe the material's resistance to deformation and are fundamental in
defining the elastic properties of soils and rocks.
Soil and Rock Stiffness
Stiffness, or the ability of soil or rock to resist
deformation, is another key geotechnical property linked to seismic velocities.
Higher velocities typically indicate stiffer materials. The modulus of
elasticity (Young's modulus) can be estimated from seismic velocities; Poisson's ratio, which can be derived from the
ratio of P-wave to S-wave velocities.
Applications in Geotechnical Engineering
The integration of seismic velocity measurements into
geotechnical investigations enhances the understanding of subsurface conditions
and aids in the assessment of properties such as:
- Soil
Compaction: Higher P-wave velocities often indicate well-compacted
soils, while lower velocities may suggest loose or poorly compacted soils.
- Soil
Liquefaction Potential: S-wave velocity is a critical parameter for
evaluating soil liquefaction susceptibility, with lower velocities
indicating higher liquefaction potential.
- Rock
Quality: The quality and fracture density of rock masses can be
inferred from seismic velocities, where higher velocities are indicative
of more competent rock.
Primary seismic velocity (P-wave) and shear velocity
(S-wave) are essential parameters in both geophysical and geotechnical
contexts. Their measurement provides valuable insights into subsurface
properties, which are critical for resource estimation, site characterization,
and hazard assessment. The relationships between seismic velocities and
geotechnical properties enable the indirect determination of material density,
porosity, stiffness, and other mechanical characteristics, making them
indispensable tools in the field of geotechnical engineering.