Abstract
Abstract This study concerns the creep impact on strength parameters of the selected very cohesive soils (PI = 30–70%). The analysis refers to Neogene clays characterized by a complex structure, resulting directly from a complicated load history in the geological time scale and identified glacitectonic deformations. In the process of samples’ preparation for strength tests as well as during the interpretation of the post-failure state, particular attention was paid to the soil structure. The imaging methods (X-ray densitometry and computer microtomography) enabled the comparison of the soil structure and the selection of samples with similar characteristics. The completed program of strength tests consisted of two series of tests in the triaxial stress state, differentiated by the occurrence of the initial creep stage, preceding the typical strength test scheme under undrained conditions. This study allowed to obtain a quantitative assessment of the influence of the creep process on the strength parameters of tested soils. Constant stress lower than 60% of the shear stress deviator leads to the deceleration creep course (m parameter 0.64–0.89). As a result, higher values of internal friction angle (20% increase comparing to triaxial tests without creep stage) and cohesion reduction are obtained from triaxial creep tests. Creep parameter m is found to be a valuable indicator for differentiation of landslide activity trend. The tests proved low values of axial strains (1–5%) at failure, which was associated with lithogenesis. By the implementation of obtained strength parameters into the 3D finite element model of the slope, the potential influence of the creep process on the stability of an exemplary cross section of the Warsaw slope could be determined.
Highlights
The diversity of the strength parameters of the soil depends on many factors, among which structural features are significant
The soil shows a constant rate of deformation, which corresponds to the value of m = 0
Controlled structural features of soils are important factors influencing the reduction of slope stability
Summary
The diversity of the strength parameters of the soil depends on many factors, among which structural features are significant. They result from the genesis and postsedimentation transformations of sediments, which have been determined by complex, sometimes multi-stage geological history. The soil genesis affects the course of geodynamic processes within the slopes. Both large-scale shears due to sudden landslide movements as well as slow creep are considered in the slope stability analysis, whereas the second factor is less frequently analyzed. The creep process is considered as a displacement of soil materials along the slope with different speeds and intensities. The character of creep refers both to slow displacements of quasi-stiff parts of soil materials and the internal deformations of the soil caused by the constant or variable non-failure load
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