| Author: | Teng, Jingcheng |
| Title: | Behaviour and modelling of sand-filled GFRP pile-wall system in reclamation engineering |
| Advisors: | Dai, Jian-guo (CEE) Yin, Zhen-yu (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Reclamation of land Foundations Piling (Civil engineering) Fibrous composites Retaining walls Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xx, 191 pages : color illustrations |
| Language: | English |
| Abstract: | To address the scarcity of land resources, super-fast large-scale economical marine reclamation is a feasible solution adopted by governments worldwide. To expedite the construction process, a novel composite pile wall system comprising an outer glass fibre-reinforced polymer (GFRP) tube filled with dense sand or cemented sand is developed in this study. This innovative pile allows for easy and immediate utilization of general fill material, i.e., sand, while reducing the use of cementitious grout materials and thus significantly reducing the carbon footprint and contributing to construction sustainability. However, the performance of this novel hybrid GFRP pile-wall system in marine reclamation engineering has not been explored. Against this background, this thesis investigates for the first time in the world the mechanical performance of the above-mentioned novel GFRP composite piles through a series of structural tests with simulations according to the actual reclamation working condition. A total of 12 GFRP stub columns and 10 GFRP piles are prepared for axial compression tests and four-point bending tests, respectively, in order to investigate the mechanical performance of the proposed novel composite GFRP piles. The key investigating parameters include the type of infill materials and the thickness of the GFRP tube. Optical Frequency Domain Reflectometry (OFDR) monitoring technology is employed to record the surface strain distributions of the tube during loading. The test results reveal that the presence of sand cores and cemented sand cores can provide internal support for GFRP tubes, preventing buckling failure and resulting in excellent ductile response under both compression and bending. Compared to sand-filled GFRP stub columns, cemented sand-filled GFRP stub columns exhibit significantly increased initial stiffness but slightly reduced peak load and ductility. With increasing axial displacement, the strength of the sand core eventually exceeds that of the cemented sand core due to the compressive hardening behaviour of the former. In the case of flexural members, the presence of a sand core effectively prevents ovalization and compressive buckling failure typically observed in hollow GFRP piles, leading to improved ductility, though the improvement in flexural bearing capacity is insignificant. On the other hand, cemented sand-filled GFRP piles not only exhibit excellent ductility but also demonstrate significantly increased stiffness and strength as compared to GFRP hollow piles. Both the stiffness and strength of the hybrid GFRP pile gradually increase as the strength of the cemented sand core increases. However, the effect of increasing the GFRP tube thickness is more pronounced. It is worth noting that increasing the tube thickness may lead to over-confinement of the internal cemented sand core, resulting in a reduced rate of pile strength improvement and the occurrence of slip between the cemented sand core and the GFRP tube. The composite action between the ductile GFRP composites and the highly ductile infill materials (i.e., compared to conventional concrete) enhances structural performance. Furthermore, theoretical modelling of the stress-strain behaviour of GFRP-confined cemented sand under compression and bending is systematically conducted. The interface behaviour between soil and pile is also a critical aspect that influences the long-term performance of the pile structure. Notably, compared to traditional piling materials (e.g., concrete or steel), GFRP composites exhibit lower stiffness and hardness, which may lead to sand particles plowing into the surface of the GFRP plate that causes abrasion and affects the behaviour of pile-soil interaction. Therefore, a series of interface shear tests have been carried out to investigate the interface behaviour between sand and GFRP composites with varying levels of hardness (i.e., though using different types of epoxy resins), with a particular emphasis on the abrasive surface wear of GFRP composites. The results of monotonic tests indicate that, under a given shear displacement and normal stress, the softer GFRP plate exhibits a higher interface friction angle and more pronounced dilation behaviour. Upon repeated tests, the interface friction angles of the softer GFRP specimens decrease due to the surface wear along the shear direction, while the overall surface roughness of the GFRP plates gradually increases. Finally, a series of physical model tests are conducted to assess the deformation performance of this new pile retaining wall system under strip loading. The effect of strip footing width at two different loading positions is investigated. The test results show that as the distance between the strip footing and the pile wall decreases, the ultimate bearing capacity of the footing also decreases, accompanied by the increased deflection of the pile wall. A wider strip footing manifests more elevated ultimate bearing capacity and settlement, inducing more pronounced deflections in the pile wall. Numerical simulations are performed using the finite element method (ABAQUS). After validating the finite element model with experimental results, a comprehensive parametric study is conducted to examine the effects of sand filling and the geometry of the GFRP cross-section on the load transfer mechanisms and deformation characteristics of the GFRP pile retaining wall system to simulate different scenarios encountered in the reclamation engineering. |
| Rights: | All rights reserved |
| Access: | open access |
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