| Author: | Li, Penglin |
| Title: | Experimental investigation and numerical modelling of clay slurry consolidation considering creep |
| Advisors: | Yin, Jianhua (CEE) Yin, Zhenyu (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Dredging spoil Dredging Soils -- Creep Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxviii, 277 pages : color illustrations |
| Language: | English |
| Abstract: | Large amounts of dredged material are generated in waterways (e.g., rivers, and lakes) and harbors every year. The rapid and efficient treatment of these dredged materials is a key issue in geoenvironmental engineering. Dredged materials usually exhibit undesirable physical and chemical characteristics such as high water content, high compressibility, low permeability, time-dependent behavior, and contamination. A typical beneficial reuse approach for dredged materials is to replace natural sands as filling materials in practical projects, such as reclamation projects. For contaminated dredged materials, further treatment in confined disposal facilities (CDFs) is required. Both in reclamation projects and CDFs, dredged materials in high water content need dewatering/consolidation. To accelerate the dewatering/consolidation process, applying prefabricated horizontal drains (PHDs) assisted by vacuum preloading is an effective method, following further strengthening by surcharge/vacuum loading with the prefabricated vertical drains (PVD). Large strains often occur during the consolidation process of these dredged materials. However, existing experimental studies investigating the consolidation behavior of clay slurry can be further enhanced, and the PHD-assisted consolidation characteristics are still not thoroughly understood. There is a dearth of developed finite strain consolidation models capable of incorporating soil creep. This thesis systematically conducts experimental investigations on clay slurry including oedometer tests using a modified apparatus and the PHD-assisted consolidation model tests. Finite strain consolidation models are developed by introducing a time-dependent compression constitutive equation and the complex interaction between consolidation and solute transport. The oedometer test results reveal that initial water content has a significant influence on the soil compressibility parameters including recompression index Cr, compression index Cc, and creep index Cα . Empirical equations are derived according to the oedometer test results to calculate the remoulded yield stress and its corresponding void ratio. Non-linear compression features are more obvious for Kaolin clay with initial water content larger than 3.5 times the liquid limit. A novel non-linear compression model incorporating a compression limit is proposed and its efficacy in describing the nonlinear compression behaviour of very soft soils is validated. Subsequently, an enhanced digital image correlation (DIC) method suitable for very soft soils is proposed and applied to explore the nonuniform consolidation behaviour of PHD-assisted consolidation. The evolution of the soil column is examined according to the displacement velocity field and void ratio distribution obtained through image analysis. The distributions of excess pore water pressure, water content, and undrained shear strength are also discussed to describe the nonuniform consolidation of very soft soils with PHDs under vacuum loading. Further, an enhanced elastic visco-plastic (EVP) constitutive equation, for describing the nonlinear compressibility and creep of very soft soils during finite strain consolidation, is developed and incorporated into the finite strain consolidation models to simulate the one-dimensional (1D) consolidation of soils with and without PHD or PVD under vacuum loading. The performance of the proposed numerical models is verified by comparing the numerical solutions with the results from existing models and measurements from model tests and field tests. Finally, for contaminated dredged materials treated in CDFs, solute transport also occurs. The design service life of CDFs and construction in the reclaimed area is usually ten or even hundreds of years. The dewatering process of dredged materials involves a typical long-term, fully coupled process, including finite strain consolidation coupling solute transport. It is important to consider the interaction between the consolidation process and solute transport, but this aspect is neglected by many existing models. To fill this research gap, the interaction effects between consolidation and solute transport (i.e., consolidation-induced solute transport and chemico-osmotic consolidation) are incorporated into the proposed numerical model. The fully coupled model was verified mathematically and experimentally by comparing it to the existing numerical solution of one-way consolidation-induced solute transport and oedometer tests exhibiting obvious mechanical and chemico-osmotic consolidation. |
| Rights: | All rights reserved |
| Access: | open access |
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