CPT Pore Pressure

[NBRY1]

How is the equilibrium pore pressure determined?
Is it a measured or calculated value?

 

[GeoEnvGuy]

The equilibrium pore pressure is typically determined by pore pressure dissipation tests just below the inferred phreatic level, this is not shown in the typical CPT plot. Pore pressure dissipation tests measure the equilibrium pore pressure at the depth tested. Pore pressure dissipation plots are provided as separate file to indicate the depth of the test, the time interval and the pore pressure reading. Looking at your attached picture I can find at least two tests were completed, the first being between the first and second dashed lines and another between the 6 and 7 dashed lines.

 

[Okiryu]

Not sure if this is what you are asking for but my understanding is that the pore pressure measured during CPT is the shear-induced pore pressure during the test. So, you may need some piezometers to measure the in-site pore pressures. Plot the hydrostatic pressure (u=gamma water x depth) and compare it against the piezometer measurements. If the measured pore pressures are close to the hydrostatic pressure line, you may consider that the pore pressures are in equilibrium. This may be helpful to see if consolidation is on-going (measured pore pressures higher than hydrostatic pressures) or if consolidation is nearly to completion (measured pore pressures close to hydrostatic pressures).