| Author: | Chen, Xiaoyu |
| Title: | Investigation of sinkhole formation mechanisms by single-layer soil-water coupled smoothed particle hydrodynamics method |
| Advisors: | Leung, Yat-fai Andy (CEE) |
| Degree: | Ph.D. |
| Year: | 2023 |
| Subject: | Sinkholes Soil mechanics Groundwater flow Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xvii, 250 pages : color illustrations |
| Language: | English |
| Abstract: | The formation of near-surface sinkhole is a large-deformation process and is often associated with complex hydro-mechanical interactions. It often occurs suddenly with significant economic loss, public inconvenience, and even human fatalities, especially in crowded urban areas. However, the understanding on the failure mechanism and governing factors of this kind of sinkholes are still limited due to the complex soil-water interactions and limitations of many existing numerical methods. The smoothed particle hydrodynamics (SPH) method is a popular mesh-free methods and has been applied to geotechnical engineering to simulate the large-deformation processes involving soil-water interactions. Considering the limited studies on the sinkholes and the unique features of SPH method, this study proposed a single-layer soil-water coupled SPH to simulate and investigate the failure mechanism and governing factors of seepage-induced sinkholes. The proposed single-layer soil-water coupled SPH involve a single type of particles that carry both the mechanical and hydraulic properties of the geomaterials, without any background mesh. The pore water pressure is updated by considering hydraulic gradients and the volumetric strain from large deformations. The mass conservation equation, motion equation, constitutive model, and Darcy’s law are incorporated at each time step to balance computing consumption and calculation. The associated boundary treatment and stability techniques are also updated with the proposed soil-water coupled method. The method is validated by simulating small-strain and large-strain self-weight consolidation problems and comparing the simulation results with the analytical solutions or other numerical solutions. The good agreement between the SPH results and other solutions indicates the accuracy and capability of the proposed method. In addition, the selection of the timestep, initial particle interval are evaluated based on parametric study, which provides reference for the subsequent application of the method. A physical model of the seepage-induced sinkhole was set up and several experiments were conducted and then simulated by the proposed method to demonstrate its capabilities and to investigate the system response under different hydraulic conditions. An improvement of the proposed method is introduced to dynamically detect changes in the free surface and boundaries around the underground opening. The good agreements on patterns of failure propagation, pore pressure response and soil displacement profiles at various stages of the experiment suggest that the proposed method can capture the key features of sinkhole developments and serve as a promising tool to explore the associated failure mechanism. Based on those achievements, the failure mechanism and influences of the governing factors are further investigated by simulating two sets of experiments with different soil types. Both the experimental results and numerical simulations indicate that an underground cavity could form and be sustained in soils with high shear strength, eventually resulting in a sudden collapse of sinkhole; while weaker soils could not sustain a sizable cavity and gradual surface displacements occur. To further explore the mechanisms behind these observed differences, a parametric study is conducted by considering variations in mechanical and hydraulic properties. A simple quantitative framework is then proposed to characterize the various types of sinkholes. The influences of mechanical properties and hydraulic conditions on sinkhole formation processes are also revealed. |
| Rights: | All rights reserved |
| Access: | open access |
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