Preliminary Investigations of Creep Strain of Neogene Clay from Warsaw in Drained Triaxial Tests Assisted by Computed Microtomography

Abstract

Abstract:The study concerns soil creep deformation in multistage triaxial stress tests under drained conditions. High resolution X-ray computed microtomography (XμCT) was involved in structure recognition before and after triaxial tests. Undisturbed Neogene clay samples, which are widespread in central Poland, were used in this study. XμCT was used to identify representative sample series and informed the detection and rejection of unreliable ones. Maximum deviatoric stress for in situ stress confining condition was equal 95.1 kPa. This result helped in the design of further multistage investigations. The study identified the rheological strain course, which can be broken down into three characterizations: decreasing creep strain rate, transitional constant creep velocity, and accelerating creep deformation. The study found that due to multistage creep loading, the samples were strengthened. Furthermore, there is a visibly "brittle" character of failure, which may be the consequence of the microstructure transformation as a function of time as well as collapse of voids. Due to the glacial tectonic history of the analyzed samples, the reactivation of microcracks might also serve as an explanation. The number of the various sizes of shear planes after failure is confirmed by XμCT overexposure.

Contemporary overview of soil creep phenomenon

“…The figure 3 shows the creep evolution by means of a graph showing the increase in soil strain at a time of constant stress. The author's experience with triaxial creep tests (e.g., Kaczmarek et al, 2017) confirmed Kisiel's description (1982) that soil creep dynamics is dependent on "strength reserve".…”

Experimental research on consolidation creep characteristics and microstructure evolution of soft soil

“…At the microscopic level, there are some popular methods being used to explore the microstructure of the soil, such as optical microscopy, scanning electron microscope (SEM), environmental scanning electron microscopy (ESEM) (Sun et al, 2019), Mercury intrusion porosimetry (MIP), and computed tomography (CT) scanning (Kaczmarek et al, 2017). Based on these microscopic test means, the main microstructure forms and creep mechanism of soil can be described qualitatively.…”