Schematization of shear strength

Abstract

The Water Authority Rivierenland is responsible for periodically assessing the safety of the dike trajectories in the Alblasserwaard region. In 2012, the safety assessment for inner slope macro-stability was performed based on stress dependent design values for the shear strength, based on the cell test
collection of the Water Authority. The most recent assessment on the inner slope macro-stability of the Lekdijk has shown a significant deviation from the previous assessment. According to these results, large scale reinforcement works are requested. Before starting any additional soil investigation, the water authority is interested in investigating the sensitivity of the schematization of the shear strength. The transition from the cell test collection to the triaxial and direct simple shear test collection, and therefore the transition from using the Mohr-Coulomb calculation model to the SHANSEP formulation, is expected to have the most impact on the outcome of the macro-stability safety assessment. The influence of the two test collections on the macro-stability safety assessment is analyzed by using a D-Geo-Stability model from the previous safety assessment for one cross-section of the Lekdijk, and transferring the model to D-Stability. The D-Stability model with the cell test collection parameters and the Mohr-Coulomb shear strength calculation model can be adjusted to the triaxial and direct simple shear test collection with SHANSEP shear strength calculation model. The transition from drained to undrained modelling results in a decrease of the shear strength of the soil around the failure surface. Therefore, the transition from the previous to the new test collection has resulted in a lower safety factor in the macro-stability analysis, having a negative impact on the overall macro-stability safety assessment.