A slab track is used for the primary railway track structure for shinkansen, and it is composed of a concrete bed, filling layer (cement asphalt mortar), RC track slab, and so on. It has been reported that some aged slab tracks laid after the 1980s have voids between the RC track slab and filling layer due to degradation of the filling layer. In the maintenance of the slab track, it is important to detect such voids at an early stage and repair them appropriately. In this study, we investigated a method for detecting voids by non-destructive testing by impact acoustics. As a result, we found that impact acoustics generated in this testing can be influenced by hammering position and supporting condition as well as the existence of voids. Furthermore, it was considered that supervised machined learning is an effective approach for the detection of voids. However, we do not consider the independence of learning data and test data in this study. It is necessary to be verified separately about the discrimination performance for the test data with clear independence such as the measured data from another slab tracks.

 Japan’s asphalt mixture has started recycling in the early 1980s and has repeatedly reused, so in recent years, the deterioration of asphalt contained in regenerated aggregate has progressed in recent years. However, test methods for evaluating of asphalt's deterioration on the quality of reclaimed asphalt pavement (RAP) have not been established. In this study, we developed three new methods of mechanical properties of RAP. The normal temperature range is evaluated by the SCB test, and the high temperature range is by two-points bending test. And the low temperature range is evaluated by NAT-SCB testing. These three types of tests revealed the effect of aging of recycled aggregate, addition of regenerating additive, and the type and amount of novel asphalt on the mechanical properties of the RAP. Moreover, we devised a new addition method which enhances the permeability of the regeneration additive, and the effect was confirmed by manufacturing by actual plant and test pavement by actual road.

 The Pavement Diagnosis Researchers Group (PDRG) has implemented a program to train and develop young engineers capable of performing detailed surveys of early-stage deterioration in paved roadways. The program utilizes knowledge management techniques based on the SECI model (socialization, externalization, combination, and internalization). In this program, young engineers work together with moreexperienced engineers to conduct detailed investigations (collaboration). Through this experience, the young engineers acquire and share implicit knowledge (socialization); convert implicit knowledge into explicit knowledge through analysis and consideration (externalization); extract new explicit knowledge through the creation of reports (combination); and incorporate the results (internalization). In a survey administered after the program, participants reported that they had acquired new explicit knowledge and felt that they could apply it at their respective workplaces. Furthermore, to assess the onsite needs for such programs, we also investigated the current state of engineer training and development at small and midsized paving companies on the northern Japanese island of Hokkaido.

 In this study, in order to measure quickly the results equivalent to the Mr test in the field and to enable appropriate bearing capacity evaluation of subgrade in the theoretical structural design of pavement, estimation method of material parameters used for Mr calculation from portable FWD test results using the multilayered theory was examined. As a result, it was found that the calculation point can be set from the forward analysis using the multilayered elastic theory, and that the material parameters can be obtained using regression equation of Mr from the stress state at the calculation point. In addition, by analyzing past Mr test results, it was found that the depth of the calculation point and the elastic modulus of the subgrade can be approximated by the linear equation.

 Structural design of asphalt pavement is to decide the necessary thickness and layer with consideration of bearing capacity of subgrade, standing under the expected heavy traffic loads in design period. However, it is still unsure how long the pavements designed by conventional method can perform its durability and structural life in fields. This 10 years research shows a clear concept and appropriate way to establish a new structural design method, which refer to the real fatigue phenomenon of asphalt pavement, clarified by the decade field survey on the deterioration actually occurred in motorways. It is a historical proposal to dramatically increase the reliability of the structural design of asphalt pavement.

 Sinkhole accidents on urban roads are induced by the collapse of an underground cavity that expands mainly because of the soil drainage from the cracks of sewer pipes. Although ground-penetrating radar is broadly utilized for detecting cavities, an evaluation method for determining whether the detected cavity exhibits risks of eventually causing sinkholes has not been established to date. In this study, small modelscale experiments were conducted to simulate cavity expansion. The tested materials exhibited grain size distributions that were similar to those of the backfill soils, which are typically used in practical sites. Two conditions were varied: the fines content of the materials and width of the aperture, which opens at the bottom of the soil chamber for simulating cracks in sewer pipes. Experimental results indicated that the cavity collapse and approaching the surface can be evaluated by 10% or 20% grain size related to the permeability, and that cavity size enlargement can be evaluated by 85% grain size, which determines the minimum width of the cracks that lead to continuous soil drainage without clogging. Finally, an evaluation method is proposed based on the aforementioned factors and other common material properties, such as weathering potentials or soil improvement that affect the cavity growth.