Residual Pore Pressure Technique

Ups is the reference residual pore pressure Ov is the in-situ vertical effective stress 

Note 1. ICU is the isotropically consolidated undrained triaxial test 

Determination of the residual pore water pressure. (From Kirkpatrick, W.M., and Retmie, I.A., Stress relief effects in deep sampling operations, Proceedings Underwater Construction Conference, University College, Cardiff, 1975.) 

Ratio of measured residual pore pressure to predicted reference residual pore pressure UJU  

Correlation of data for predicting strength changes resulting from sample disturbance Santa Barbara channel sediments. (From Chaney, R.C., and Demars, K.R., Strength Testing of Marine Sediments, ASTM SIP 883, American Society for Testing and Materials, Philadelphia, PA, 558, 1985. Reprinted with permission from ASTM.) 

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NAPL, especially when distributed discontinuously, may show little or no tendency to move unless the applied hydraulic gradients are extremely high, beyond what is normally achieved in the field (Fig. 3-25). The same problem of residual saturation occurs during the recovery of oil from a petroleum reservoir a significant fraction of the petroleum cannot be recovered even with the most advanced techniques. In coarse soils, NAPL with sufficient vapor pressure can sometimes be recovered below residual saturation by volatilization into the air in pore spaces, and subsequent removal of the air... 

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