There is a concern that polymer flocculants used in the flocculation and settling processes of construction sludge contain a toxic unreacted monomer material. Therefore, a new intermediate treatment process is necessary to reduce the amount of polymer flocculant added while maintaining the required flocculation performance. Furthermore, at present, owing to the shortage of disposal spaces and the decrease of cement demand, paper sludge ash (i.e., PS-ash) generated from the paper production process should be reused in new applications. In order to reduce the amount of polymer flocculants to be added, PS-ash is employed as a material to assist the flocculation by combining a polymer coagulant with an inorganic coagulant during the coagulation sedimentation stage. Consequently, it was confirmed that the electric zeta potential of the clay slurry suspension was decreased by the addition of PS-ash and the aggregation performance was highly improved. In addition to this, it was confirmed that the addition of PS-ash to construction sludge reduced the elution of a fluoride material originating from the sediment.

The author’s research group has proposed a new improvement method for waste sludge and dredged sediment in construction sites using fine paper made from used paper (hereafter referred to as fine shredded paper: FSP). Previous studies have proved that the addition of fine shredded paper (FSP) improves the transportability of the high-water content clay due to increase of the strength of the treated clay. However, the FSP treated clay is insufficient for proper use as a geomaterial when the original clay has an extremely high moisture content. In this study, we investigated the mechanical properties of the FSP mixed treated clay with cement by uniaxial compression tests in order to examine the applicability as a geomaterial. The results indicated that the combination of FSP and cement is likely to reduce the difference in stiffness between FSP-cement treated clay and surrounding ground, which is a concern in the case of cement stabilization. The FSP mixed treated clay with cement will be more compatible in stiffness with the surrounding ground. This mechanical characteristic may derive from the water absorption and reinforcement effects of the FSP fibers.

For the Kanto Loam cement stabilized soil, the mix proportion that satisfies both fluidity and strength was examined. In the experiment, 3 types of cement were used, and the relationship between the water content ratio and the flow value was first investigated under the condition that the water cement ratio was constant. Then, unconfined compression tests were performed under both 4 conditions of water cement ratio and 4 conditions of flow value. In the examination of the mix proportion of the cement stabilized soil, two conditions of on-site strength of 500 kN / m² and 3000 kN / m² were set, and the mix proportions under 3 types of cement and 4 conditions of flow value were obtained. Finally, the characteristics of the mix proportion were considered from the comparison of the cement mass and soil particle mass in the cement stabilized soil.

Since ground improved by sand compaction pile (SCP) method involves complex characteristics, in addition to density increase induced by compaction, the entire improved ground may have higher liquefaction resistance than that obtained from SPT N-value taken in-between the sand piles. To elucidate the effects peculiar to SCP-improved ground, the authors carried out a research aimed at more sophisticated ground improvement evaluation by focusing on the change in microstructure due to cyclic shear application. Here, model experiments simulating the SCP construction using an X-ray CT (Computed Tomography) scanner were conducted, and the ground behavior around the sand piles during sand pile construction was examined through image analysis. As a result, it was found that the change in soil microstructure in the SCP-improved ground can be evaluated by the number of contact points between soil particles, and that SCP-improved ground has larger number of contact points than that induced by pile densification method where piles are left in the ground, indicating a more effective anti-liquefaction effect.

In recent years, the number of cases of the groundwater lowering method as a countermeasure against liquefaction has been increasing. In Osaka and Kobe areas, since the alluvial sand layer is loosely deposited on the surface and the groundwater level is high, damage due to liquefaction is expected in the event of an earthquake. However, in the lower part of the alluvial sand layer, the alluvial clay layer, which has undergone large subsidence due to the past pumping of groundwater, is thickly deposited. We predicted ground settlement by groundwater lowering, using shallow subsurface model constructed from Kansai Geo-informatics Database and the result of ground investigations conducted independently. We also predicted liquefaction potential at the present groundwater level and after the groundwater lowering within the allowable ground settlement. As the result, it was found that liquefaction countermeasure can be obtained by groundwater lowering.

The ground freezing method is one of the ground improvement methods for excavation protection in tunnel construction, etc. In the clay layer, the effect of freezing expansion on the structure increases due to the excess frozen soil after the creation of the frozen soil thickness required. Therefore, minimizing this effect is an important task of the ground freezing method. One of the measures against frost heaving has been thermal control of the position of the frozen soil surface using a heat fence, and empirical control of freezing has been successfully performed. In this study, we proposed a method of applying the freezing heat analysis method used in design and construction management for frozen soil thickness control, and verified its applicability using actual examples of frozen construction. As a result, it was clarified that the proposed method is practically effective, and it was possible to quantitatively demonstrate that frost heave is controlled by suppressing the increase in frozen soil thickness by the heat fence method.

In this study, we conducted triaxial compression elongation test, hollow cylindrical torsional shear test and simple shear test on undisturbed viscous soil and reconstituted clay, so that loading direction, loading mode, loading speed and compaction stress history on the static mechanical properties of viscous soil. Brittle strain softening, which is cited as a representative dynamic behavior of the non-disturbing clay with outstanding skeleton structure, is observed depending on the loading speed by triaxial compression test, and it is a small loading speed and a simple shear mode, It was shown that the degree of softening decreased and it became impossible to observe it, so it was not an absolute mechanical property of the clay. In addition, it was shown that the anisotropy attributable to the initial structure is small in the non -disturbing viscous soil sample used in this study.

We have developed two types of reinforced soil walls using chains as reinforcing material: walls mainly made of steel pipes and walls made of cylindrical wire mesh, and have constructed them at various sites. Reinforced soil walls constructed at wind power generation sites are temporary but important structures, since heavy vehicles which transport heavy items such as blades and towers frequently make round trips on the temporary access road, and large cranes construct wind turbines in wind turbine yards. We investigated the chain reinforced soil walls constructed on the access road and the wind turbine yard for nine months, due to the concerns about deformation caused by the large load during its construction. As a result, no significant deformation occurred. All the chain reinforced soil walls were constructed within standard value for as-built management, and the amount of maximum displacement observed was as small as up to 6 mm at the access road and up 24 mm at the wind turbine yard.

One of the main causes of subsurface cavities, which may lead to road cave-ins that frequently occur in urban area, is the outflow of soil at the breakage of buried pipes. Many studies on the generation and expansion processes of those types of cavities have been conducted so far. Recent excavation investigations at the sites of subsurface cavities revealed that there are cases where only water leakage gaps, which cannot be regarded as breakages, exist in the joints of sewer pipes below the cavities. These gaps have not been associated with the cause of subsurface cavities. In this study, the mechanism and influential factors of the generation and expansion of subsurface cavities caused by water leakage points of sewer pipes were investigated by a series of model experiments. It was confirmed that subsurface cavities are induced even by small gaps in the joints of sewer pipes.

More than twenty deep-seated landslides occurred by the heavy rainfall in July 2018 in Tajikawa river basin at Otoyo, Kochi, Japan. They destroyed a bridge of an express highway and gave much damage to local roads and river structures while gave no damage to human lives. Micro-topographic features in the slopes with the landslides were examined by field investigation and LiDAR DEM with 1 m resolution. It was revealed that the landslide at 2018 occurred within an old landslide and other old landslides near the ridge existed above the landslides at 2018. Fresh cracks and steps were identified just above the upper boundary of the landslides at 2018. These cracks and steps might have been generated due to the reactivation of the old landslides near the ridge by the rainfall.

Ageing underground infrastructure and intensifying natural disasters increase underground cavities and the risk of road collapse, so prevention is necessary. Determining the expandability of the explored cavity and predicting the time of depression will optimise the survey plan and repair time and realise an effective and efficient maintenance cycle. Unfortunately, there are few records of the expansion process. For this reason, monitoring surveys were conducted on ten existing roads with 55 cavities under the road surface. As a result of radar exploration for two years every six months, expansion of 7 holes and new 28 cavities were confirmed. In addition, the 12 cavities in the sandy soil were investigated in detail during the repair. As a result, multiple events were identified in which the earth and sand flowed out from the small gaps created in the buried pipe, and the cavities were formed.