To determine mechanical properties of soil, specimens may be consolidated to the estimated conditions in-situ before being tested. The in-situ vertical effective stress is estimated from density measurements of the soil layers above. The in-situ horizontal effective stress is usually inferred from profiles of overconsolidation ratio with depth or derived from in-situ tests. An alternative method for estimation of the horizontal effective stress is desirable to reduce the duration of usually sequential laboratory testing in projects and to produce more reliable estimates of horizontal stress for soils like glacial clay that have low voids ratio owing to several shearing sequences rather than due to overconsolidation. Therefore, a tensiometer has been developed that is installed in triaxial cells or used as a standalone unit at site laboratories to measure soil matric suction immediately after soil samples are recovered. Triaxial isotropic loading/unloading tests showed that the tensiometer can measure negative pore-water pressure with an average error of 1%. Soils suction from different offshore sites was measured and was mostly higher than the best estimate in-situ mean effective stress. Test results showed that tensiometers can be used to reliably determine in-situ horizontal stress when a sample is of good quality and retaining its effective stress.
Amin Rismanchian, Tim Carrington, Karl Snelling and Jerry Sutton
Keywords: high matric suction, saturation, triaxial, site investigation, in-situ horizontal stress
Publisher: DFI