SEISMIC Tests :

The objective of the seismic survey is to estimate the P- and S-wave velocities down to a depth of 50 m at one specified location within the site. Terraloc Pro, from ABEM company, can be used for all seismic surveys :

• Down Hole Test (ASTM D7400)

The Down Hole Test is a method which determines soil stiffness properties by analyzing direct compressional and shear waves along a single borehole. P- and S-waves are generated on the surface using a sledge hammer. A borehole geophone (S) or hydrophone string (P) is used to receive signals.

• Cross Hole Test (ASTM D4428)

The Cross Hole Test is a method which determines soil stiffness properties by analyzing direct shear waves between boreholes. S-waves are generated using a shear wave source between dry or water filled boreholes. A borehole geophone is used to receive signals. Source and receiver need clamping to borehole wall.

• Reflection

Reflection seismic is commonly used to delineate subsurface horizons from surface measurements. Downward propagation seismic waves generated by a surface source are going to be reflected at any layer interface having a different acoustic impedance. The reflected wave field is received at the surface by geophones. S-wave reflection survey can be done with high resolution down to about 50m.

• Borehole tomography

Seismic tomography images the space between boreholes. Typically, P-waves are generated in one borehole and received in the other borehole. A high resolution structural image is calculated based on travel times.

• MASW

The surface wave seismic (MASW - Multi channel Analysis of Surface Waves) is a method which determines soil stiffness properties by analyzing Rayleigh type surface waves down to about 15 to 30 m. Rayleigh waves are generated at the surface by a vertical hammer impact. Geophones arranged in a line are used to acquire signals.