Tetsuya Tokoro

Influence of Freeze-Thaw Action on Hydro-mechanical Behavior of Unsaturated Crushable Volcanic Soils

The objective of this study is to evaluate the effect of freeze-thaw action on the strength and water retention-permeability characteristics of crushable volcanic coarse-grained soils in unsaturated conditions. A series of triaxial compression tests, water retention tests and permeability tests were performed for volcanic coarse-grained soils under different freeze-thaw histories. Test results showed that the particle breakage caused by the freeze-thaw action made the shear strength in unsaturated conditions decrease and the water retentivity increase, while not affecting the permeability. These indicate that the freeze-thaw action has strong influences on the hydro-mechanical characteristics of a crushable volcanic coarse-grained soil in unsaturated conditions even if the soil lacks in frost-susceptibility.

Coupled Thermo-Hydro-Mechanical Analysis of Freeze–Thaw Behavior of Pavement Structure over a Box Culvert

Evaluation of frost heave is essential for good design of a geotechnical structure in cold regions. Frost heave often causes severe roughness and cracking of structures like pavements. To model frost heave around a box culvert, a practical coupled thermo-hydro-mechanical (THM) model is presented. The performance of the proposed THM model, which can predict the freeze–thaw behavior of unsaturated soil, is demonstrated through frost heave tests under different conditions. A pavement structure located above a box culvert was simulated, and the analysis could reproduce phenomena observed in the field, including uneven upheave of the pavement and frost-heaving force induced by frost-susceptible backfill. To mitigate such damages, the mechanism and countermeasure of uneven frost heave were investigated. It was revealed that the freeze–thaw action considerably affects smoothness and failure of the pavement structure. In addition, the use of insulation may reduce roughness and extend the fatigue life of the pavement structure. The findings of this study are useful for minimizing frost heave in geotechnical structures.

A Finite Element Analysis of Stress Change in Pavement Subjected to Freeze-Thaw

The prediction of stress change in pavement structure is quite essential for the design, construction, and maintenance of pavement in the seasonal cold region. Much attention is concentrated on the change of elastic modulus of soils due to freezing and thawing. To overcome the limitation of conventional design method, in which the elastic modulus of materials needs to be assigned manually to various thermal state layer by layer, a comprehensive analysis method is proposed in this study. This analysis can specify temperature-dependent modulus, and a typical pavement in the cold region was selected and simulated. It is revealed that snow cover on footpath can affect the thermal pattern in the pavement, which leads to differential frost penetration along the cross-section of the pavement. The stress change induced by frost action of soil shows the reverse trend between frozen and unfrozen (thawed) layers. The stress increment in subgrade during spring season should be accounted properly.

Frost heave analysis of ballasted track above box culvert and its influence on train vibration

The uneven frost heave of frost-susceptible subgrade soil causes track irregularity, which highly enhances train vibration and affects the comfort and safety of railway transportation. This paper presents a coupled thermo-hydro-mechanical (THM) analysis for the freezing behavior of railway located above a box culvert. The vertical acceleration of the vehicle, an indicator of riding comfort, is predicted through a vehicle dynamic model. The results reveal that the existence of a box culvert changes the subgrade thermal pattern, leading to a deeper frost penetration depth. The frost heave amount above the box culvert is larger than the adjacent section, resulting in uneven track structure upheave and track irregularity. This frost-induced track irregularity highly affects train vibration.

Influence of Various Experimental Conditions on Shear Behavior of Compacted Sandy Soil under Unsaturated Condition

The objective of this paper is to examine the influences of moisture content, loading speed, and degree of compaction on the shear behavior of compacted sandy soil under unsaturated conditions. A series of triaxial compression tests with various experimental conditions were carried out by using triaxial apparatus for unsaturated soil. The test results show that the shear strength of unsaturated soil decreases with the increase in moisture content and increases due to increment of loading speed. The effect of degree of compaction is also discussed. The results reveal that moisture content, loading speed, and degree of compaction have strong influences on the shear behavior of unsaturated sandy soil.