The strength of construction materials at historical sites built since the Edo era was investigated using the rebound hammer test and evaluated with regard to construction age, facility usage, and kind of materials. The tested materials were rocks (andesite, granite, and sandstone) at 18 sites, concrete at 23, and brick at 9. The strength of the first strike was smaller than that obtained with subsequent hits at the same position. The strength increased by increasing the number of hits until it became constant after several strikes. The mean values and coefficient variations of the strength for stone and brick were not influenced by the age of construction or facility type. An unique relationship has been observed between unconfined compressive strength and dry density for rocks and bricks. This relationship does not depend on the rock type of stone or on the ordinary, burned, or refractory bricks of the bricks.

The acquisition of new engineering technologies through biomimetics is a major approach in the civil and mechanic fields. Some species of bivalves are known to dig into the sand with high energy efficiency and low force using only their shells and foot. The purpose of this study is to reveal the mechanism of reduction of penetration resistance and energy loss by this foot movement. The author flowcharted the foot motion by biological observation, formulated a model of foot penetration, and conducted penetration experiments using a texture analyzer. As a result, it was found that the thickness, shape, and non-action part of the foot contributed to the reduction of penetration resistance.

High-pressure jet grouting is one of the common columnar soil improvements. Although its extensive utilization, a mud-like mixture, slurry, is ancillary generated during the application. The slurry is mainly floating soil particles with water which occurs in two ways: (1)-during the cutting water application and (2)- during the binder material injection. That means most waste slurry arises from the input materials, water, and binder. Therefore, decreasing the inputs might be a basis for the waste slurry reduction. This research suggests using a superabsorbent polymer aqueous solution as a jet grout cutting material for improving cutting performance and substituting the traditional way (water use). The applicability of the recommended method was examined with laboratory and in-situ experiments. In conclusion, the cases which use the superabsorbent solutions generate less slurry than the traditional method, although they have similar engineering performance values (strength and fluidity).

In recent years, momentum has been rising to use large-size soil-bag to permanent recovery work as for road quick recovery due to the slope disasters that often occur along mountainous roads. In order to obtain the fundamental data for diverting large-size soil-bag to permanent recovery work a series of full-scale experiments of rock fall are conducted in this study. The behavior, the damage state, and the application range of impact energy of the protection wall made with large-size soil-bag are investigated by full-scale tests. It was found that, the laminated soil-bag wall structured of 6×3 soil-bags on the bottom layer, 5×2 soil-bags on the middle layer, and 4×2 soil-bags on the top layer was able to catch the falling rock impact energy of 1,300kJ. Furthermore, it was confirmed that the number of soil-bags reacting against impact becomes larger with increasing the impact energy.

In order to solve the problems related to subsurface cavities in urban areas, a joint research project between industry, government and academia from 2018 to 2020 was carried out. It has analysed existing cavity data, conducted laboratory model experiments, numerical analysis, full-scale field tests and cavity monitoring on the road, and attempted to develop a "series of rational processes for investigation planning, cavity exploration, collapse risk diagnosis and cavity repair". Based on the analysis of the formation and expansion mechanisms and actual conditions of cavities, a cavity potential map, a collapse risk assessment index and a menu of cavity repair and prevention measures were developed. Here, an overview of the cave-in prevention solution and a full-scale field test are reported. A full-scale test road with artificial cavities was constructed and loading tests were conducted on the road surface to elucidate the cavity behaviour in order to develop a cave-in hazard assessment and repair method that takes the road structure into account.

It has been reported that the deformation greatly increased in the secondary consolidation process in the past long-term consolidation test of 1.8 years on Na-type bentonite/sand mixed soil. Therefore, we analyzed potential contributing factors in this behavior. A long-term consolidation test for about 10 years on bentonite and kaolinite was started using the test equipment with countermeasures against these factors. In this paper, the secondary consolidation behavior of bentonite was investigated based on the long-term consolidation test data for 2.7, 3.7 and 4 years. The results were generally consistent with the conventional findings on soil mechanics that the deformation due to secondary consolidation progresses linearly with respect to logarithm of time. This test will be continued for about 10 years and longer-term secondary consolidation behavior will be investigated.