Geotechnical probesBesides the advantages of using the CPTU test, we have the possibility of carrying out seismic tests in conjunction with the CPTU. These tests allow simple, low cost measurement of the wave velocity Vs. This combination of tests gives us the survey we call SCPTu.

The wave velocity (Vs) is a basic property of all solids which corresponds in engineering terms with the stiffness to small deformations (γ<10-6), termed G0 or Gmáx.= ρVs2, where ρ is the density of the material.

The modulus G displays a non-linear behaviour, i.e. it decreases considerably as the deformation level increases. The diagram below shows a theoretical graph of the range of deformation for which the CPTU test is valid and the levels of deformation where the most common geotechnical problems occur.

 

 

Various studies have demonstrated that the Vs values determined from the SCPTu surveys in normally consolidated soils (NC), is repeatable and is the same as that measured using the cross-hole technique although at a much lower cost.

 

The SCPTu is appropriate for use in any situation in which the CPTu test is used, thus improving on the already excellent data the latter provides. The combination of the two tests offers a major contribution to geotechnical investigation.

 

 

Advantages and applications

  • Speed.
  • No previous survey necessary.
  • Classic CPTU results, plus wave velocity Vs.
  • Combination of measurement of stiffness at very different deformation levels in a single instrument.
  • Analysis of degradation of stiffness and G modulus.
  • Analysis of liquefaction