What Does Compressional Wave Velocity Mean?
Compressional wave velocity is a measure of the velocity with which sound waves pass through soil and rock strata. It varies with porosity, lithology, degree of fracturing and bulk density of the earth material. Site investigation for trenchless construction includes both soil and rock depending on geology, and the degree of saturation greatly influences the compressional wave velocity.
Different methods such as suspension logging, seismic refraction, crosshole test, and downhole test are used to measure compressional wave velocity.
Trenchlesspedia Explains Compressional Wave Velocity
Suspension logging provides both shear and compression wave velocity measurements in a single hole at depths greater than 200 feet. It offers high resolution as less as 20 cm for resolving thin layers, that can affect the surface response. It is not affected by path effects near a soil-rock interface or in steeply dipping beds and is optimized for soil and soft rock, providing better penetration and accurate results. Crosshole testing is conducted near the surface (the upper hundred meters) and determines the compressional and shear wave velocity of materials.
The downhole test measures the travel time from the time of wave generation until observed by a receiver and predicts the velocity propagation required by elastic waves i.e. compressional and shear wave to propagate through the soil under consideration.