IGS can provide in situ seismic testing through seismic profiling of Shear wave (Vs) and Compression wave (Vp) velocities in combination with any of our CPTu and DMT testing. The seismic testing modules can be connected both a DMT blade (developed by Marchetti) or a CPTu cone. This has been made possible by cooperation between two of our valued suppliers, Marchetti and Geomil. The use of these modules is everyday practice for IGS.
IGS uses the latest “fixed interval” seismic profiling equipment for the collection of S-wave velocities. This is a quantum leap in data reliability and repeatability compared to traditional down hole pseudo-interval profiling methods. Our Seismic equipment has been developed and supplied by our good friends at Marchetti - Please follow the link to visit the Official Marchetti Website.
The seismic module is a tubular element placed above the CPT cone/ DMT blade, equipped with two receivers located at 0.5 m distance. When a shear wave is generated at the surface, it reaches first the upper receiver, then, after a delay, the lower receiver.
The seismograms acquired by the two receivers, amplified and digitized at depth, are transmitted to a PC at the surface, that automatically calculates the delay using the Cross-Correlation algorithm.
The shear wave velocity is obtained as the difference in distance between the source and the two receivers (S2 – S1) and the delay ΔT from the first to the second receiver. The true-interval test configuration with two receivers avoids possible inaccuracy of the “zero time” at the hammer impact, sometimes observed in the pseudo-interval one-receiver configuration.
Shear wave velocity data processing is:
The Shear wave velocity profiling can be conducted in materials ranging from very soft clays to strong rock by executing the test in a borehole backfilled with gravel (Totani et al. 2009).
The SPDMT or SPCPT is an enhanced version of the "S" unit containing two additional sensors for recording compression waves (Vp).
Once again, the seismic module is a tubular element placed above the CPT cone/ DMT blade, equipped with two receivers located at 0.64 m distance. When a compression wave is generated at the surface, it reaches first the upper receiver, then, after a delay, the lower receiver.
The seismograms acquired by the two receivers, amplified and digitized at depth, are transmitted to a PC at the surface. Both the upper and lower wave forms are assessed using the Marchetti ELab software to provide two series of data from the same profile.
Our Seismic equipment has been developed and supplied by our good friends at Marchetti - Please follow the link to visit the Official Marchetti Website .
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