Sediment shear strength. Using the laboratory T-bar and effect of the diameter

Résumé

Dehydration of the dredged sediments is necessary in different operations of sediment valorization: lagunage, handling and transport of sediments. The evaluation of hydric properties (WC water content, LL liquidity limit, PL plastic limit, SL shrinkage limit) and of undrained shear strength Su must be made to ensure the follow-up of these operations (slopes stability, reversal of wind-rows in lagunage basins, bearing capacity of engines circulating on layers of sediments, consistency of the sediments, effect of remolding under cyclic request,…), rate of dehydration or drying. In first approach, the relation Su–WC could answer the problems posed. Measurement of the water content WC can be given by sampling; these samples obtained which also make it possible to follow the evolution of the components of the sediments (environmental properties, OMC organic matter content, pollutants level). For measurement of undrained shear strength, two laboratory tools are transposable on site: Vane Shear Test (VST) and the T-Bar Test (TBT). The first provides discrete measurements of Su, the second, continuous measurements. This last is sometimes used in laboratory. TBT Test can be used in vertical alternate cycles (penetration-extraction) and record the degradation of undrained strength. This tool allows the establishment of the relation Su–WC. Once presented the T-Bar Test geometry, kaolin clay properties and experimental set-up are given. Some geometry influences, (diameter, proximity, roughness) are commented.