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.

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.

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.

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.

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.