University of Twente Student Theses
Mechanical response of soil mixtures under Freezing and Thawing processes
González Pérez, N. (2024) Mechanical response of soil mixtures under Freezing and Thawing processes.
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| Abstract: | This study investigated the mechanical response of soil mixtures subjected to freezing and thawing cycles (abbreviated to FT cycles in this report). The research focused on understanding how these cycles affect the shear strength characteristics of various soil mixtures, which is especially crucial for construction in cold regions where cyclical freezing and thawing of the ground occurs multiple times throughout the year. The study consisted of conducting the direct shear test on mixtures of sand and clay. Initially six mixtures of differing proportions of sand and clay were prepared, but two were soon discarded. Per mixture three batches of three samples each were tested, so nine samples per mixture in total. The batches pertained to the state of the samples when being tested: dry, saturated, and subjected to FT cycles. The tests measured the shear force, vertical displacement, and horizontal displacement under an imposed normal stress. This normal stress was predetermined and differed per sample in a batch of a mixture, so that each batch consisted of identical samples each tested with a different normal stress. From the experiment measurements, parameters such as void ratios, volume deformation, shear stress, cohesion and friction angle were derived and analysed. The findings indicated that soil mixtures with a fine content of 20% or above demonstrated an erratic mechanical response under FT cycles, but also when saturated or when dry. It was seen that for these mixtures the shear strength decreased for increasing normal stress and showed no difference between dry, saturated and FT states, which opposed the main hypotheses drawn from the literature. An important finding was that these mixtures often had excessive contraction which rendered them unfit for shear testing. In the case of the mixtures with a fine content below 20%, the shear strength generally increases with higher normal load. These mixtures showed more predictable behaviour, with clear trends in shear strength and volume deformation. However, the strength of the dry samples was not always greater than that of the FT samples, another main hypothesis of the literature. This led to the conclusion that a higher degree of FT cycling is necessary to observe more pronounced results, meaning lower freezing temperatures and more cycle iterations. The study concluded that FT cycles can significantly impact the mechanical properties of soil mixtures, but a higher degree is needed to fully visualize this impact. Further research is recommended especially in terms of the high fine content mixtures to investigate the erratic behaviour shown in this study and justify it. Additional further testing could also incorporate refinements to the methodology, particularly in the preparation of samples, the measurement of important parameters such as the void ratio, and considerations of more intense FT cycling. |
| Item Type: | Essay (Bachelor) |
| Faculty: | ET: Engineering Technology |
| Programme: | Civil Engineering BSc (56952) |
| Link to this item: | https://purl.utwente.nl/essays/104505 |
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