University of Twente Student Theses


Effects of Natural Vegetation Root systems on the shear strength of soil. Comparison of effectiveness of vegetation root system reinforcement and fiber reinforcement

Matyunin, A.A. (2022) Effects of Natural Vegetation Root systems on the shear strength of soil. Comparison of effectiveness of vegetation root system reinforcement and fiber reinforcement.

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Abstract:This study investigated and compared the effects of root reinforcement and Polypropylene (PP) fiber reinforcement on the shear strength of unsaturated sand. The plant that was chosen to grow and develop in sand is common Maize (Zea Maize L.), since it can freely develop a root system in coarse sand with the addition of a nutrient solution. Sand is chosen as a soil since it is the most available soil for analysis. Several mathematical models were taken as a basis for this study, namely the Pallewatha et al. (2019) model for rooted soils, the Tarantino and Di Donna (2019) model is used for unsaturated soils and the Maher and Grey (1990) model is used for analysis of fiber reinforced soils. Since in this case it is necessary to develop plant life in the tested samples, the unsaturated soil approach had to be taken. The tests were performed by means of a Direct Shear Cell device, in which constant vertical stress is applied while horizontal stress changes in accordance to the set shearing rate. In order to not disturb the soil integrity of rooted samples, several shea boxes were 3D printed to use both as a growing container and a part of the testing apparatus. The plants were grown in a growing chamber with constantly maintained temperature and moisture conditions, as well as a simulated daytime cycle. After testing, the rooted samples were exhumed to acquire root volume by image segmentation to determine the volume of the fiber to be used in the comparative testing. The results of testing rooted samples showed one major trend, which was that plant roots do not perform well in terms of shear reinforcement at high values of normal stress, while at lower values of normal stress plants perform quite well. As well as that, several connections between plant age, the volume of the root and the density of the root were identified as influences on the shear strength reinforcement capacities of the root system, which meant that root behavior could not be predicted linearly by growing period as initially assumed. The results of fiber reinforced samples were directly compared to the results of the plants from which the fiber volume was acquired to achieve the most direct comparison. In all cases fiber reinforcement underperformed when compared to root reinforcement, which could be due to several factors. One is that rooted samples on top of the mechanical effect of the roots utilize a suction mechanism which results from evapotranspiration of moisture from the soil. Therefore, the general performance of rooted samples was better. However, the underperformance of fiber samples could be due to the stolen void ratio effect and the fact that the chosen fibers were too short to entangle with each other and simulate root performance. The study was subject to several limitations, the most major of which was the limited time frame since it restricted the number of tests that could be performed on the rooted samples and as a consequence on the fiber reinforced samples. As well as that, some equipment and material problems were present, which resulted in a significantly smaller number of shear boxes being 3D printed. Further studies could focus on creating a systematic picture of plant root influence on the shear strength of soil, especially with regards to how much influence can be attributed to variables like plant age, suction, root stiffness, root volume and how they are interconnected.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Programme:Civil Engineering BSc (56952)
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