Constant Rate of Strain Consolidation Testing of Saturated Cohesive Soils Without Back Pressure Saturation

Abstract

Abstract ASTM D4186/D4186M-12, Standard Test Method for One-Dimensional Consolidation Properties of Saturated Cohesive Soils Using Controlled-Strain Loading, requires back pressure saturation for all specimens to accurately measure pore fluid pressure and flow behavior. Constant rate of strain (CRS) consolidation testing performed without back pressure saturation has the potential to provide significant time and cost savings, as the need for costly back pressure saturation equipment and the time required for specimen back pressure saturation would be eliminated. The results of one-dimensional CRS consolidation comparison tests performed with and without back pressure saturation on high quality Sherbrooke block and 76-mm diameter modified tube specimens and on reconstituted specimens of low overconsolidation ratio, soft, saturated clays are presented herein. Comparison of the compression curves from specimens tested with and without back pressure saturation, especially at stresses greater than the estimated in situ vertical effective stress, show good agreement. Flow behavior between the two types of specimens is more erratic at low stresses but becomes more comparable as the effective stress level increases. It can be concluded from the results that accurate CRS consolidation stress–strain behavior can be measured for saturated specimens tested without back pressure saturation for stresses greater than the in situ vertical effective stress.