UROP Proceedings 2020-21

School of Engineering Department of Civil and Environmental Engineering 91 Shear Strength Properties of Hydrophobic Soil Supervisor: LEUNG Anthony / CIVL Student: LI Sau Long / CIVL Course: UROP1100, Fall Hydrophobic sand, which has been utilised to minimise rainfall infiltration, is investigated for its possible use in slope stabilisation. However, how the application of the silicone coating may affect the mechanical behaviour of hydrophobic soil including the shearing properties has rarely been investigated. The purpose of this study is to design and develop a new apparatus, which can monitor any pore water pressure changes during a direct shear test and can determine the effects of suction on the shearing behaviour of hydrophobic soil. The hydrophobicity in sands can be attained by artificially applying a layer of silicone coating, polydimethylsiloxane (PDMS). Various mass ratios of dimethyldichlorosilane (DMDCS) is mixed with Toyoura sand to produce PDMS coatings by silanisation. In this project, a preliminary direct shear test, 25 and 50kPa tests and a validation test on only untreated and unsaturated samples were conducted. Results gave reasonable trends with increasing normal stress but formed shear stress peaks less prominent than expected. In the future, the shear strength and dilation behaviour of treated samples will be studied through suctionmonitored direct shear tests. Engineering Properties of Soil Amended by Hydrochar, a New Resource Derived from Food Wastes Supervisor: LEUNG Anthony / CIVL Student: WAN Ngo Yeung / CIVL Course: UROP1100, Fall Hydrochar is charcoal derived from biomass and has been used for soil amendment and modifying the soil properties. However, effects of hydrochar on the geotechnical properties including shear strength are unknown. This project investigates the effects of biochar on the shear strength properties of a local soil, completely decomposed gravel (CDG). Direct-shear tests were conducted to compacted CDG samples in order to measure soil’s shear stress, vertical displacement, and horizontal displacement. It is found that hydrochar increases the vertical displacement of dry CDG but decrease that of moist CDG (at optimum water content). Hydrochar has minimal effect on the shear stress of dry CDG but decrease that of moist CDG. Hydrochar decreases the friction angle of both dry and moist CDG. Recyclable Hydrogel-Based Brick for Construction on Mars: A Feasibility Study Supervisor: QIU Jishen / CIVL Student: NGAN Man Cheuk / CVGBM Course: UROP2100, Fall This study aims at investigating the feasibility of recycling hydrogel-based bricks and the impact to its mechanical properties after recycle process. Our research object is Gelatin as it provides high recyclability with little requirement of additional chemical agents and environment condition. Compression tests and SEM analysis are conducted to examine the impact of recycling bricks to the stress, elastic modulus and failure modes of the hydrogel-sand composites. The bricks recycled by heating with water only can attain an elastic modulus of 177.4MPa and a compressive strength of 6.45MPa, which is about 70% of the original strength before recycling.

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