Inflow and outflow permeability tests in a very soft clay under low stresses

Abstract

In situ inflow and outflow permeability tests with the BAT probe at Sarapuí II soft clay test site are presented. A description of the BAT permeability test is provided, discussing its advantages and shortcomings, especially in the case of very soft clays under low stresses. Pore pressures were monitored during probe installation and were found to be slightly lower than piezocone u2 pore pressures, consistent with the position of the filter. The role of filter tip saturation was investigated after the usual saturation procedure provided an unsatisfactory pore pressure response during probe installation. Results show that the vacuum saturation procedure provides adequate response during installation and increases the reliability of the coefficient of permeability determination in early measurements. Both inflow and outflow tests yielded similar results, indicating that careful execution of the test can lead to good test repeatability regardless of the loading condition. Various sequences of alternated inflow and outflow tests have yielded similar results, indicating that soil reconsolidation and filter clogging were negligible in the tests performed. Data are presented concerning the relationship between index parameters and the in situ coefficient of permeability for Sarapuí II clay, which plot outside the range of existing databases.