Ballasted railway track
Ballasted track sleepers serve an important function of providing sufficient lateral resistance to prevent the lateral movement of rails. If the lateral force induced by the thermal expansion of the steel rails overcomes the lateral resistance of the sleepers, rail buckling may occur. However, there is a high degree of uncertainty over the prediction of the lateral resistance of sleepers. In view of the foregoing discussion, a series of laboratory tests were performed on 1/5-scale models to evaluate the lateral resistance of the sleepers. Single-sleeper pullout tests and track panel pullout tests were performed on different types of concrete sleepers. The results of the pullout tests revealed the effects of the sleeper shape, sleeper spacing, and number of sleepers on the lateral resistance.
Here, I introduce my research projects that I recently carried out with my collaborators.
Airport pavement
A heat-reflective pavement is well known for reducing the pavement temperature. So far in Japan it has been used to sustain the heat island effect particularly in urban areas. On the other hand, these days severe rutting problems are observed in the asphalt pavement at the main airports such as the Haneda International Airport and Narita International Airport in Japan. In this study, attempts were made to introduce a heat-reflective pavement into an airport pavement to solve these rutting problems.
Schematic view of lateral instability of ballasted tracks
Track panel pullout test
Pavement damage observed in the National Highway
Recycling of the existing old asphalt layer
Road pavement
Reasons for pre-mature failures and applicable measures against those failures occurring in National Highways in Bangladesh were investigated. Under the periodic and maintenance programs, 50-mm bituminous overlay (BO) work over existing old asphalt surface is typically suggested. Owing to repeated BO work, pre-mature failures occurred immediately after the construction had been completed. We conducted an analysis and indicated that the pavement life reduced due to the coupling effect of interface bond failure and overloading. On the basis of the calculated results and the site conditions, two measures were suggested: one measure involved the conversion of the existing old asphalt layer to a stabilized cement base layer, and the other measure involved the combination of the new and old asphalt layers to a single asphalt layer using the RAP technology.
Trial construction of heat-reflective pavement
Surface temperature of airport asphalt pavement with or without heat-reflective coating
Soil stabilization
A new method for granulating liquid muds was proposed. This method involves the crumbling of partially cemented muds. Laboratory experiments revealed that the cone indices of the cement-mud mixtures obtained immediately after they are primary cured can be used to control the possibility of granulation and the size of particles, irrespective of the water content and the primary curing period of the muds. We also found that the granulated soils are light in weight, have high porosity, and exhibit characteristics that are similar to those of conventional granular materials. The test results indicate that the granulated soils show high potential for use in materials such as reclamation, subgrade, or backfill materials.
Trial construction of motocross tracks using the granulation method
Laboratory experiments performed on granulated soils
Sustainable geotechnical design
In the recent decades, while a large amount of dredging materials has been drived from the coastal or lacustrine areas in various countries, the development of infrastructure requires a large amount of high-quality soils for reclamation, embankment or backfilling materials. The utilization of dredged soil as construction material with appropriate engineering properties and reasonable cost has been a big challenge for geotechnical engineers. Attempts were made to utilize paper sludge ash (PSA) and fly ash (FA) to improve the engineering characteristics of dredged soils. The water absorption performances of PSA and FA were found to play key roles in the improvement of soil characteristics.
Dredged soils with high water content
Paper sludge ash
Laboratory geotechnical testing
Several types of laboratory tension tests exist for cement-treated soils and soft rocks. However, Brazilian split tests do not give the tensile strength of cement-treated soils or that of soft rocks accurately, because the actual loading conditions are far from the theoretical assumptions. On the other hand, uniaxial and triaxial tension tests require considerable efforts and craftsmanship techniques to set up the required specimen. We therefore developed a new method to obtain the tensile strength of cement-treated soils and soft rocks. We obtained the tensile strength of Tage tuff, mudstone, and cement-treated soil by applying centrifugal acceleration to the specimens. The tensile strength obtained from the centrifugal tension tests was compared with that obtained from the Brazilian split tests and uniaxial tension tests.
Uniaxial tensile test
Centrifugal tensile test
Flow out of railway ballasts
SPH simulation
Numerical modeling
Recently in Japan, railway ballasts have been flown out several times by heavy or intense rainfalls. However, the mechanism by which the railway ballasts have been flown out has not yet been investigated in detail; therefore, the risk associated with such a mechanism as well as the countermeasures against such a mechanism cannot be reasonably proposed. Therefore, in this study, a permeability simulation of railway ballast was reproduced using a smoothing particle method (SPH), with focus on the permeability of a ballast bed. It was found that the permeability characteristics of ballast track-beds can be expressed on the basis of Forchheimer’ law, and not Darcy’ law. Thus, we proposed a model that can reproduce Forchheimer’s law, as well as performed some permeability simulations for verification. The permeability simulation of a ballast bed yielded reasonable results as compared with those obtained from experiments.