Stability of tree in structural cell in unsaturated soil mixtures
Date of Issue2016-05-17
School of Civil and Environmental Engineering
Singapore is a green urban city with millions of trees planted around the country. Many of them are located beside pavements and roads. Concrete pavements and roads laid above compacted soil leads it to carry the traffic load near the trees reducing the space for roots to spread and as a consequence also limit the root growth. Hence, structural cells have been proposed to improve this problem since structural cells provide spaces for root to grow. As different soil mixtures acting as tree planting medium inside the structural cells may have different properties as well different shear strengths, one of this FYP project scope is to carry out laboratory tests and numerical modeling to investigate the effect of different soil mixtures with the presence of structural cells on the stability of trees. Multistage consolidation drained unsaturated (CD) triaxial tests and numerical modeling using SIGMA/W were carried out on two soil samples, ASM Top soil and soil mixture comprising of 50% gravel chips and 50% ASM Top soil. The soil samples were taken from the site in Bukit Timah where the pilot study about structural cell has been conducted. The results from the triaxial tests suggested that for soil mixtures of low compaction, the shear strength of the soil mixture when gravel chips made up 50% of its content did not give much improvement if compared with 100% ASM Top Soil which has a higher degree of compaction. In conclusion, the results obtained showed that the most stable tree planted in a structural planting space is the 7m high tree followed by 9m and then 5m high tree. Secondly, the degree of unsaturation does not have an effect on small trees, i.e 5m high trees used in this study but has some notable effect on the bigger trees. Thirdly, the increase in root length is the most effective for 7m trees when root length was increased from 1.6m till 2m. Lastly, the trees planted in the soil without gravels (ASM Top soil) are more stable as compared to trees planted in soil which contains 50% of gravels.
Final Year Project (FYP)
Nanyang Technological University