University of Twente Student Theses
Influence of different pore fluids and micro mechanics and shear strenght of non-active clay
Jacobs, D.H.J.E. (2019) Influence of different pore fluids and micro mechanics and shear strenght of non-active clay.
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| Abstract: | The objective of this Bachelor Assignment was to find out the influence of the different pore fluids on the micro mechanics and shear strength of non-active clay. This objective was divided into different research questions. One question focused on the influence of the pH-level of the pore fluids, another on the influence of the dielectric permittivity. Also the influence of the different OCR states was investigated. The last research question was to find out what micromechanisms would be responsible for the observed behaviour on macro level. The first result that was observed is that for pH 4 water the ultimate strength is smaller than the critical strength, even though they should have been the same. For the pH 9 water both ultimate strength and critical strength had the same value. This difference in behaviour can either be explained by looking at the different ways of interpreting the Mohr Circle, but it can also be explained by looking into the difference in microstructure. Further research into the microstructure of the clay using the MIP method could help understanding these mechanisms, but this was out of the scope of this bachelor assignment. The difference in ultimate and critical strength can also be explained by looking at the Taylor’s equation. This equation holds for sand, but it is not sure whether it also holds for clay. In the report it is proposed that this equation should have an additional term that takes into account the elastic energy. For sand this term would become negligible, but for clay not. Taking into account the elastic energy would explain the difference in ultimate and critical strength, but also the fact that the peak strength does not occur at the maximum dilatancy and that pH 9 does not have a peak. Another result is the difference in friction angle of the failure envelopes for the pore fluids with different values of dielectric permittivity. The research of Pedrotti and Tarantino (2017) already showed this difference upon 1D compression, but now it is shown that this difference also occurs upon shearing. Why this difference in shear strength can be observed between the pore fluids with different dielectric permittivity again can be explained by looking at the microstructure. The higher the repulsion between the particles, the bigger the angle between the particles in edge-to-face configuration. What happens at micro level that causes particles with a bigger angle to have a higher shear strength still has to be found out by doing further research on microscopic level. A conclusion that was drawn upon these results is that for clayey soils elastic energy has to be taken into account while looking at the Taylor’s equation. (Taylor, 1948). This would mean an additional term needs to be added to the equation. A detailed explanation can be found further in this report. |
| Item Type: | Essay (Bachelor) |
| Faculty: | ET: Engineering Technology |
| Subject: | 56 civil engineering |
| Programme: | Civil Engineering BSc (56952) |
| Link to this item: | https://purl.utwente.nl/essays/80734 |
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