SEISMIC DOWN-HOLE/CROSS-HOLE TESTING
Instrumentation for geognostic investigation
This type of survey is performed for the mechanical characterisations of grounds crossed during the probing phase. The technique consists in the measurement of the travelling times of the elastic waves between the seismic source on the surface and the geophones located inside the probing hole, properly conditioned with PVC pipe or geo-technical pipe. The seismic exploring activity in the down-hole takes place by placing one or more triplets of sensors (horizontal and vertical) inside one of the probing holes and at various depths, aimed at receiving the seismic signals generated through ram on anchored plate. Energy will be supplied in phase inversion in order to polarise phases S on a horizontal plane H, according to an orientation of 180°. Through seismic speeds Vp and Vs, it is possible to obtain information, such as elastic modules and geo-seismic parameters. Vs 30 can be measured on probing holes up to 30 metres of depth (O.P.C.M 3274/2003).