| 1. |
- Do, Tan Manh, et al.
(author)
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Numerical analysis of the tunnel uplift behavior subjected to seismic loading
- 2022
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In: Journal of Mining and Earth Sciences. - : Hanoi University of Mining and Geology. - 1859-1469. ; 63:3a, s. 1-9
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Journal article (peer-reviewed)abstract
- Seismic loading has always been a major concern for any engineering structures, and thereby, underground facilities (e.g., tunnels) are not exceptional. It is due to the seismically induced uplift and instability of tunnels caused by the large deformation of liquefiable soils. Therefore, the tunnel uplift behaviors subjected to seismic loading are always taken into account in any designing stages of tunnels. This study's main goal was to evaluate how a tunnel buried in liquefiable and non-liquefiable soils would behave when subjected to seismic stress. Seismic and liquefaction potential assessments of the soils surrounding the tunnel were carried out using the finite-element method. In this study, PM4sand, an advanced constitutive model was adopted in all finite-element models. In addition, the uplift displacement and excess pore pressure of liquefiable soils were studied, under a typical earthquake. Investigations were also conducted into how the thickness of the non-liquefiable soil affected seismic loading, tunnel uplift displacement, and the buildup of excess pore water pressure. As a result, during the earthquake, liquefaction was triggered in most parts of the sand layer but not in the clay layer. In addition, the tunnel uplift displacement was triggered due to the relative motion and interaction at both sides of the tunnel. In addition, this study found that the thickness of the non-liquefiable soil layer (sand layer) had a significant impact on the build-up of excess pore water pressure and, consequently, the tunnel uplift displacement. The uplift displacement and excess pore water pressure build-up were higher the thinner the non-liquefiable layer was.
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| 2. |
- Do, Tan Manh
(author)
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Excess pore water pressure generation in crushed and fine granular materials under cyclic traffic loads
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Excess pore water pressure can develop in subgrades of railway and pavement substructures due to cyclic loading from heavy traffic, leading to the migration of fine particles into upper layers. This migration can clog pores and diminish the drainage capacity of upper layers,negatively impacting the long-term performance of sub-structures and service life, ultimately risking failure. Therefore, understanding the mechanisms behind the accumulation of excess pore water pressures and the migration of fine particles under cyclic loading is essential for efficient and cost-effective maintenance methods. The main objectives of this research include (1) investigating excess pore water pressure generation in crushed and fine granular materials under cyclic loading, (2) evaluating the migration of these materials into upper layers under cyclic loading, and (3) simulating a practical application using an advanced model to provide valuable insights into the operation of structures subjected to cyclic traffic loads while considering real-world factors from the field.A series of cyclic triaxial tests were conducted to investigate the generation of excess pore water pressure in fine granular materials. Two types of fine granular materials, tailings (a crushed material) and railway sand (a fine granular material) were selected for this investigation. The cyclic characteristics of these materials, including cyclic axial strain and excess pore water pressure, were evaluated in terms of number of cycles and applied cyclics tress ratios (CSR). As a result, the cyclic axial strain and excess pore water pressure were observed to accumulate over time due to cyclic loading. However, the extent of accumulation was found to be significantly dependent on CSR values and material types. In addition, a relationship between excess pore water pressure and cyclic axial strain of the fine granular materials was established and proposed based on the results from the undrained cyclic triaxial tests (including both tailings and railway sand samples).To assess the migration of fine granular materials into overlying layers under cyclic loading, a modified large-scale triaxial system was employed as a physical model test. A quantitative analysis of material migration was based on the mass percentage and grain size of migrated materials collected at the gravel layer. Additionally, cyclic responses (strain and excess pore water pressure) were evaluated. As a result, the total migration rate of the tailing sample was significantly higher than that of the railway sand sample. The migration analysis on tailings also revealed that finer tailings particles exhibited a greater tendency to migrate into the upper gravel layer compared to coarser tailings particles under cyclic loading. This migration could be attributed to significant increases in excess pore water pressure during the final cycles of the physical model test. The findings from this research could make a valuable contribution to the existing literature concerning the accumulation of excess pore water pressure and its effects on the migration of fine particles under cyclic loading.A numerical study was conducted to simulate the complex interactions between tailings materials and cyclic traffic loads on the piers of tailings dams. The integration of experimental data and advanced constitutive models enabled a comprehensive understanding of the behavior of tailings under these loading conditions. The findings focused on the build-up of excess pore water pressures in tailings subjected to cyclic traffic loads while taking into account the effects of truck loads, velocities, and truck resting times. As a result, excess pore water pressures in tailings progressively increased with the number of passing trucks, indicating a cumulative effect of loading cycles. In addition, the effect of truck loads and truck velocities on the excess pore pressure build-up was discovered, with higher truck loads and lower truck velocities leading to increased excess pore pressures, posing a greater risk. Furthermore, through anoptimization process involving variations in truck loads, velocities, and resting times, it was revealed that a combination of increased truck velocity, reduced truck load, and extended truck resting time could effectively minimize the build-up of excess pore water pressures in tailings beneath the pier. These findings offer valuable guidance for optimizing transportation operations on tailings dam piers, enhancing efficiency and safety.
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| 3. |
- Do, Tan Manh
(author)
-
Excess pore water pressure generation in fine granular materials under cyclic loading -A laboratory study
- 2021
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Licentiate thesis (other academic/artistic)abstract
- Abstract Excess pore water pressure can be generated in subgrades of both railway and pavement sub-structures under cyclic loading caused by heavy traffic. When saturated subgrades are subjected to cyclic loading, excess pore water pressures accumulate over time which then could lead to migration of particles into overlying layers. The migration of subgrade soil particles to the upper layers would lead to clogging of pores and reducing the upper layers' drainage capacity. Both excess pore water pressure accumulation and migration of fine particles could negatively affect the long-term performance and service life of the sub-structures and eventually may lead to failure. Understanding the mechanism of both excess pore water pressure and migration of fine particles under cyclic loading is, therefore, essential for not only designing but also further proposing efficient and economical maintenance methods. The main objectives of this research are to (1) investigate excess pore water pressure generation in fine granular materials under cyclic loading and (2) evaluate migration of fine granular materials into overlying layers under cyclic loading. A series of undrained cyclic triaxial tests were performed to study the excess pore water pressure generation in fine granular materials. Two types of fine granular materials, i.e., railway sand (natural granular material) and tailings (artificial granular material), were selected for this investigation. The cyclic characteristics of these materials, e.g., accumulated strain and excess pore water pressure, were evaluated in terms of number of cycles and applied cyclic stress ratios (CSR). As a result, axial strain and excess pore water pressure accumulated over time due to cyclic loading. However, its accumulations were significantly dependent on CSR values and material types. Finally, a relationship between excess pore water pressure and accumulated strain of the fine granular materials was discovered based on all outputs from the undrained cyclic triaxial tests (both tailings and railway sand samples). In order to evaluate the migration of fine granular materials into overlying layers under cyclic loading, a modified large-scale triaxial system was used as a physical model test. Samples prepared for the modified large-scale triaxial system composed of a 60 mm thick gravel layer overlying a 120 mm thick subgrade layer (tailings and railway sand). The quantitative analysis on migration of the fine granular materials was based on the mass percentage and grain size of migrated materials collected at the gravel layer. In addition, the cyclic responses (strain and pore water pressure) were evaluated. As a result, the total migration rate of the railway sand sample was found to be small. There were no migrated sand particles pumped up to the gravel surface, i.e., no mud pumping, after the test terminated. The migrated sand particles were observed and collected at the bottom half of the gravel layer. The total migration rate of the tailing sample was much higher than that of the railway sand sample. In addition, the migration analysis revealed that finer tailings particles tended to be migrated into the upper gravel layer easier than coarser ones under cyclic loading. The migrated tailings particles were observed at the surface of the gravel layer after the test ended. It could be involved in significant increases in excess pore water pressure at the last cycles of the physical model test. The findings obtained in this research may provide an additional contribution to the literature dealing with the excess pore water pressure accumulation and its effects on the migration of fine particles under cyclic loading.
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| 4. |
- Do, Tan Manh, et al.
(author)
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Excess pore water pressure generation in fine granular materials under undrained cyclic triaxial loading
- 2023
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In: International Journal of Geo-Engineering. - : Springer Nature. - 2198-2783. ; 14:1
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Journal article (peer-reviewed)abstract
- Understanding the mechanism of excess pore water pressure generation in subgrades is essential for not only designing but also further maintenance purposes. The primary goal of this research was to investigate excess pore water pressure generation in fine granular materials under cyclic loading. A series of undrained cyclic triaxial tests were performed to study the excess pore water pressure generation in two selected fine granular materials: (1) railway sand and (2) tailings. The excess pore water pressure response of these materials was evaluated in terms of density conditions, number of cycles, and applied cyclic stress ratios (CSR). As a result, excess pore water pressure accumulated over time due to cyclic loading. However, its accumulation was significantly dependent on the governing factors, i.e., densities, CSR values, and material types. The excess pore water pressure exhibited a slight increase at low CSR values, but a sharp increase was observed at higher CSR values, which ultimately led to a failure state after a certain number of cycles. In addition, under the same loading conditions, the samples that had higher relative compaction showed better resistance to cyclic loads as compared to those with lower relative compaction. Finally, a relationship between excess pore water pressure and cyclic axial strain of the fine granular materials was discovered.
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| 5. |
- Do, Tan Manh, et al.
(author)
-
Migration of fine granular materials into overlying layers using a modified large-scale triaxial system
- 2024
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In: Geomechanics and Engineering. - : Techno-Press. - 2005-307X .- 2092-6219. ; 37:4, s. 359-370
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Journal article (peer-reviewed)abstract
- The primary goal of this study is to evaluate the migration of fine granular materials into overlying layers under cyclic loading using a modified large-scale triaxial system as a physical model test. Samples prepared for the modified large-scale triaxial system comprised a 60 mm thick gravel layer overlying a 120 mm thick subgrade layer, which could be either tailings or railway sand. A quantitative analysis of the migration of fine granular materials was based on the mass percentage and grain size of migrated materials collected in the gravel. In addition, the cyclic characteristics, i.e., accumulated axial strain and excess pore water pressure, were evaluated. As a result, the total migration rate of the railway sand sample was found to be small. However, the total migration rate of the sample containing tailings in the subgrade layer was much higher than that of the railway sand sample. In addition, the migration analysis revealed that finer tailings particles tended to be migrated into the upper gravel layer easier than coarser tailings particles under cyclic loading. This could be involved in significant increases in excess pore water pressure at the last cycles of the physical model test.
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| 6. |
- Do, Tan Manh, et al.
(author)
-
Railway embankment behaviour due to increased axle loads - A numerical study
- 2021
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In: 18th Nordic Geotechnical Meeting 18-19 January 2021, Helsinki, Finland. - : Institute of Physics (IOP).
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Conference paper (peer-reviewed)abstract
- Due to an increase in axle loads, the development of excess pore water pressure and settlement in a railway track foundation of fine-grained subgrade soil can be observed. A thorough understanding of the mechanism of development of excess pore water pressure is essential for understanding the development of settlements and the design of potential ground improvement. In this paper, a three dimensional numerical study is presented, which investigates the effects of an increase in axle loads of trains on both excess pore water pressure and settlement. Special attention is given to a soft soil layer beneath the embankment and the influence of ground improvement (deep soil mixing columns). As a result, an increase in axle loads leads to a considerable increase in both excess pore pressures and settlement in the subgrade layer. This increase is more significant in the case of heavy axle load (32.5 tons) than that of the light axle load (16 tons). In addition, cyclic loading can lead to a considerable increase in both vertical displacements and excess pore water pressure. The use of deep soil mixing columns reduces excess pore water pressures and settlements significantly.
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| 7. |
- Do, Tan Manh, et al.
(author)
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Tailings fluidization under cyclic triaxial loading – a laboratory study
- 2022
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In: Geomechanics and Engineering. - : Techno Press. - 2005-307X .- 2092-6219. ; 29:5, s. 497-508
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Journal article (peer-reviewed)abstract
- Tailings fluidization (i.e., tailings behave as being fluidized) under cyclic loading is one concern during the construction of tailings dams, especially in the shallow tailings layers. The primary goal of this study is to evaluate the responses of tailings under cyclic loadings and the tailings potential for fluidization. A series of cyclic triaxial undrained and drained tests were performed on medium and dense tailings samples under various cyclic stress ratios (CSR). The results indicated that axial strain and excess pore water pressure accumulated over time due to cyclic loading. However, the accumulations were dependent on CSR values, densities, and drainage conditions. The fluidization potential analysis in this study was then evaluated based on the obtained cyclic axial strain and excess pore water pressure. As a result, tailings samples were stable (unfluidized) under small CSR values, and the critical CSR values, where the tailings fluidized, varied depending on the density of tailings samples. Tailings fluidization is triggered as cyclic stress ratios reach critical values. In this study, the critical CSR values were found to be 0.15 and 0.40 for medium and dense samples, respectively.
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| 8. |
- Manh Do, Tan, et al.
(author)
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Numerical Analysis of an Upstream Tailings Dam Subjected to Pond Filling Rates
- 2021
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In: Applied Sciences. - : MDPI. - 2076-3417. ; 11:13
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Journal article (peer-reviewed)abstract
- One of the challenges in upstream tailings dam projects is to ensure the allowable rate of deposition of tailings in the pond (i.e., pond filling rate) while maintaining the stability of the dam. This is due to the fact that an upstream tailings dam is constructed by placing dikes on top of previously deposited soft tailings, which could lead to a decrease in dam stability because of the build-up of excess pore water pressure. The main purpose of this work is to investigate the effects of pond filling rates on excess pore water pressure and the stability of an upstream tailings dam by a numerical study. A finite element software was used to simulate the time-dependent pond filling process and staged dam construction under various pond filling rates. As a result, excess pore water pressure increased in each raising phase and decreased in the subsequent consolidation phase. However, some of the excess pore water pressure remained after every consolidation phase (i.e., the build-up of excess pore water pressure), which could lead to a potentially critical situation in the stability of the dam. In addition, the remaining excess pore water pressure varied depending on the pond filling rates, being larger for high filling rates and smaller for low filling rates. It is believed that the approach used in this study could be a guide for dam owners to keep a sufficiently high pond filling rate but still ensure the desirable stability of an upstream tailings dam.
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