Evaluation of the consolidation state and strength of soft clay using shear waves

Abstract

Reliable estimation of the consolidation state and strength of soft soils is important for the prediction of permanent settlement and strength, particularly when an additional load induced by civil structure construction is added in situ. The effective stress state and void ratio value are particularly critical as they are the most important parameters for consolidation state evaluation and strength estimation. To date, the consolidation behavior of clay has been studied in various civil engineering practices. However, the existing in-situ consolidation characterization approach entails several difficulties in monitoring the effective stress and density variation during the consolidation process. This thesis focuses on the evaluation of the consolidation state and strength of soft soil using shear waves. The shear wave velocity is a function of the particle composition and inter-particle force, because the shear wave propagates through particle contact in saturated clay. Therefore, the effective stress of a clay media can be evaluated``using the shear wave velocity. Several shear wave-based laboratory tests are performed so as to monitor the shear wave velocity variation during consolidation. Piezoelectric bender element sensors are used to generate and receive shear waves inside laboratory specimens, without soil disturbance. First, the consolidation state and properties of natural clay deposits are characterized by laboratory consolidation tests using bender element sensors installed in non-disturbed Shelby tube specimens. The vertical effective stress - shear wave velocity relationship for the normally consolidated state is evaluated from laboratory tests. The in-situ consolidation state is evaluated by comparing the in-situ shear wave velocity with the estimated effective stress - shear wave velocity trend. However, the accuracy of the in-situ consolidation state evaluation depends on the in-situ shear wave velocity data. As such, reliable in-situ shear wav...