A landslide in sensitive clay was occurred after the Saguenay earthquake on 25 November 1988 in the municipality of Saint-Adelphe. The soil profile indicates that the deposit is composed of a crust of stiff clay, after the crust the deposit is composed of plastic sensitive clay with consistency soft to stiff. A geotechnical investigation has been carried out in-situ and in laboratory. In addition to the conventional tests, a new seismic simulator was used to develop a geotechnical model of Saint-Adelphe clay. A finite difference analysis has been performed to study the stability of the slope before and during the earthquake and the results show that there is a development of some plastic zone and generation of pore pressure but the global factor of safety of the slope was above the unity. A post-seismic analysis by using the strain-softening behaviour model show a propagation of plastic zone and a development of failure surface close to the observed failure surface. It is then put forward that Saint-Adelphe landslide could be explained by the progressive failure mechanism.
Stiffness degradation, G/G0, curves of Champlain clay at St-Adelphe, Quebec, and the associated variation of its damping ratio with shear strain are constructed in this study using the new combined triaxial simple shear (TxSS) apparatus. The apparatus offers the ability to obtain the stiffness (G/G0) and damping ratio of soils over a wide strain spectrum from 0.001% to 10%. The value of the small-strain stiffness of the tested clay is further confirmed through another series of piezoelectric ring-actuator technique (P-RAT) tests. Although, the stiffness degradation curve of the tested clay follows to some extent traditional curves suggested in the literature, the examined Champlain clay exhibits a different trend with respect to hysteresis damping, especially at large strains (>1%), and available analytical models could not successfully predict the damping behavior of the Champlain clay at such a strain level. A new constitutive model is therefore presented as a modification of the original Sig4 model considering the pore-water pressure built up with shear strain. Stiffness degradation and damping ratio versus shear strain curves of Champlain clays estimated using the proposed soil model are similar to their experimentally determined counterparts even at large shear strains where other models tend to misjudge the damping behavior of the clay.
The shear modulus and equivalent viscous damping ratio of three sensitive clays from the sediments of the Champlain Sea were investigated using a combined triaxial simple shear apparatus. The tests were conducted on undisturbed samples and were carried out on a wide range of shear strain from about 0.001% to 1%. The values of the small strain shear modulus of the tested clays were further confirmed through a series of piezoelectric ring actuator and MASW tests. Although the shear modulus and damping ratio of the sensitive eastern Canada clays follow some classic literature models, the results show that the examined clays exhibited more linear behaviour. Such behaviour may be attributed to their highly structured nature compared to other clays. The compilation of available data on the shear modulus and damping ratio of several sensitive eastern Canada clays confirmed this trend and showed that some literature models might not be representative.
The assessment of the strain rate effect on the geotechnical properties of soils constitutes an important step toward a more accurate analysis of their response. This study presents the experimental results of monotonic and cyclic simple shear tests performed to examine the strain rate effect on the behavior of eastern Canada soils. Eight natural soils sampled from different locations in eastern Canada were used in this study. The tests were performed on a simple shear device using a strain-controlled mode. In addition to the obtained experimental results, published data in the literature were used to draw the conclusions of this study. Analysis of the data indicates that the undrained shear strength increases proportionally with the strain rate by approximately 10–17% per log cycle of . The results also show that the secant shear modulus G increases with the strain rate, especially at large strain amplitude. Moreover, the analysis of the data revealed that the magnitude of the strain rate effect seems to be correlated with the shear strain amplitude and plasticity index (Ip). A practical application of the outcomes on the backbone curves is given in which illustrates the influence of and on the strain rate effect.
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