There is strong societal demand to improve the functions of existing infrastructure to enable active, efficient use. Requests include countermeasures against increasing logistics volume and larger ships and vessels, expansion of airport functions, and countermeasures against existing facilities which can no longer be used due to increased external forces and other reasons. In addition, regarding waste disposal sites at sea which accept industrial and non-industrial waste, there is public demand to ensure highly efficient use of the sites. On the other hand, it has become difficult to secure land for soil disposal sites which accept soil dredged from shipping routes. Accordingly, it is necessary to prolong the life of soil disposal sites.

Therefore, we will develop the following: techniques to efficiently improve and renew the functions of existing infrastructure and to efficiently change the applications of existing infrastructure; techniques to reduce or efficiently utilize construction-generated soil and other redundancy; and techniques to efficiently utilize waste disposal sites at sea.

We have already conducted research and development on improving existing facilities including deepening existing quaywalls. However, such improvements were made using techniques for newly-built structures. Hereafter, we will investigate methods of evaluating ground characteristics, design methods, and subsurface-exploration methods to improve and renew existing facilities. In such methods, the construction history, effects from neighboring structures, and other factors will be taken into account. We will also investigate ground-evaluation methods and ground databases, both of which cover residual settlement and other phenomena, with the aim of long-term facility maintenance.

We will investigate the following techniques regarding dredged soil: improvement techniques to transform dredged soil into high-value added materials including composite soil, which provides habitats for benthic creatures, and solidified soil with high water permeability; and new volume-reduction techniques. We will also investigate durability when solidified soil and slag composite soil are used in sea areas, the mechanical characteristics of composite ground materials containing various byproducts, crushable materials, and other contents, and methods of evaluating and managing the quality of these materials.

Regarding disposal sites at sea, technologies for seepage control works for construction have been developed. However, research on post-construction utilization of such sites has not progressed. Therefore, we will investigate the following which are necessary for utilization: ground-making methods, construction methods, effects on impervious layers, construction methods to manage the internal water level at low cost, techniques to detoxify waste before land reclamation, and the medium- to long-term strength and elution characteristics of solidified soil.

Based on measurements of differential settlement regarding reclaimed land, we evaluated individual phenomena through element tests, investigated overall behavior through numerical simulation using case examples, and then predicted the settlement.

We developed an experiment system which simulates a series of processes ranging from chemical grouting experiments to shaking table test using geotechnical centrifuge. We used a refractive-index matching technique to visualize the ground and developed a technique to directly observe the penetration process of chemical grouting.

We continued to conduct a model experiment regarding the ground range affecting the bearing strength of piles and the effects of structure construction and other works on the surrounding ground. In addition, we started to investigate methods of evaluating ground characteristics taking construction history into account, through numerical analyses. We also developed a construction method to improve the existing pile castings (soil-improvement work between piles) during the research.

We conducted erosion tests on steel-slag/clay composite soil and compiled the results regarding durability. The characteristics of erosion of these soils induced by water flow remained unknown, so we developed a new compact erosion test apparatus to quantify such erosion characteristics. Then, we performed a series of erosion experiments by utilizing the apparatus developed. On the basis of the results, we proposed an erodibility chart of consolidated clay, cement treated clay, and steel-slag/clay composite soil.

We conducted various trials using X-ray CT scanners and three-dimensional molding apparatus (3D printers), and then compared the numerical analysis results using the discrete element method. In a replication analysis of compression tests, we found that the reproducibility of particle-contact points is an important factor. In addition, regarding permeability issues, we found that analyses can obtain similar permeability coefficients when particle diameters and particle configurations are the same.

We continued to evaluate water-shielding characteristics regarding the peripheral surface of piles installed at a disposal site which had been filled with non-incinerated waste in 2014. We also participated in a field test of pile-installation at a waste site which had been filled with incinerated ash.