The Downhole Test is a method which determines soil stiffness properties by analyzing direct compressional and shear waves along a borehole down to about 30 m.
The aim of the downhole testing is to derive elastic rock properties such as Poissons ratio or YOUNGs modulus. Shear waves have to be generated at surface. A shear wave source (sledge hammer hit sidewise) is used at surface and a coupled receiver system is moved in the borehole.Traveltimes of the seismic waves are analysed and seismic velocity is calculated. Shear wave velocity can be transformed to soil stiffness
The measurements can be performed below and above the groundwater table. A grouted casing (e.g. PVC) with a diameter between 3 and 6 inch needs to be prepared.
Additional information can be found in: Dynamic_SoilProperties_DH.pdf