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Operative guide downhole Down-hole OPERATIVE GUIDE DOWN ?? HOLE SEISMIC MAE advanced geophysics instruments - www mae-srl it CDown-hole Down-hole seismic procedure Generality Down-Hole method represents one of the best and most accurate techniques for det

Down-hole OPERATIVE GUIDE DOWN ?? HOLE SEISMIC MAE advanced geophysics instruments - www mae-srl it CDown-hole Down-hole seismic procedure Generality Down-Hole method represents one of the best and most accurate techniques for determining physico-mechanical and dynamic properties of soils Gasperini Signanini Test aim is to produce an horizontal and vertical stress on ground surface through a mechanical source and to study P and S waves train that propagates within the ground at various depths in vertical direction with polarized vibrations in the propagation direction waves P and polarized on the horizontal plane with vibrations perpendicular to propagation direction SH waves Through a receiver made up of a geophonic backbone oriented in the three spatial directions z x y placed into the hole at known depths ?rst arrival moment of P and SH waves train is compared to the moment measured with the trigger in which the stresses are induced to the source therefore dividing for such values the distance between source and receivers P and SH waves speed can be obtained Fig Picture Execution scheme of down-hole test MAE advanced geophysics instruments - www mae-srl it CDown-hole Down-hole test allows to detect horizons at lower speeds below an higher speed level overcoming the refraction seismic limits known in the bibliography as silent horizons For down-hole seismic surveys there are many di ?erent acquisition geometries depending on how the energizing system and the receivers are arranged among themselves each di ?erent geometry gives a di ?erent name to the test We have three kind of surveys down - hole cross - hole and up ?? hole Picture In down - hole survey the elastic waves source is in surface while receivers are in hole In up ?? hole test the opposite happens that is source in hole and receivers in surface The cross - hole survey needs positioning of the source and receivers In two perforations at a distance of usually no more than ten meters Picture Di ?erent methods of acquisition for seismic surveys in hole Execution of drilling tests must be preceded by a preparatory phase in which the hole is made if this is not already available where to place the receivers or the source and a preparation phase of the recording tools During the drilling phase of the survey it is necessary to work in such a way as to minimize the disturbance on the walls and surrounding areas around the hole The drilling must be performed in rotation and it is advisable to support the walls with bentonite mud Subsequently the hole must be coated with a high vibration- resistant pipework such as PVC or ABS pipes with a thickness mm to be assembled by M F threading or glued junctions Finally the hole must be cemented at the annular space between the walls and the lining tube and closed with a packer to ensure the continuity of the ground-pipe contact MAE advanced geophysics instruments - www mae-srl it CDown-hole Methodology consists in recording at various