In this study, we developed a new method for the evaluation of the urea hydrolysis rate as a measure of soil improvement. The urease-producing bacterium Sporosarcina aquimarina isolated from the sea off the coast of Korea was selected to enhance soil strength. The soil strength of coastal regions was enhanced using a soil improvement technique based on urea hydrolysis by S.aquimarina, with less than two types of laboratory test. The main outcomes are as follows: (1) The urea hydrolysis rate can be used for a short-term evaluations using an electronic conductivity meter. (2) The soil strength determined on the basis of microbial carbonate precipitation depends on the microbial species. (3) Enhancement of soil strength on the basis of microbial functions is highly correlated to the rate at which urea is hydrolyzed by the urease-producing bacterium.

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This paper discusses horizontal coefficient of consolidation (ch) for prediction of consolidation settlement in peaty ground improved by plastic-board drain (PBD). A numerical analysis is carried out on two nearby sites of test embankments on peaty grounds improved with and without PBD. It is found that the coefficients of consolidation back-calculated from the analysis were significantly different between the grounds which were improved or not; ch for PBD improvement ground was 15 times as small as that without PBD. We deduce that water passageways locally grown in the peaty ground lead to high permeability and raise the effective coefficient of consolidation for unimproved ground. On the other hand, for improved ground, the effective coefficient of consolidation is less affected by the water passageways because of the short distance of horizontal drainage towards the PBD. As a result, The value of horizontal coefficient of consolidation ch approaches that obtained by laboratory consolidation test. In addition, our simulation shows that the effective horizontal coefficient of permeability in the peaty grounds was predicted smaller than the effective vertical one. We conclude that this result implies strong effect of disturbance induced by installing the PBD into the ground.

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At the moment in Japan, appropriate disposal management of vast amounts of disaster waste generated by the Great East Japan Earthquake, which occurred on March 11, 2011, is required. As matters now stand, although waste is being collected from across the devastated areas of eastern Japan and moved to primary and secondary provisional waste yards, practical waste disposal work is not being carried out enough, so it is necessary to propose guidelines for waste disposal for speedy rehabilitation and reconstruction. In this study, we quantified the environmental impact with respect to the tsunami debris generated by the Great East Japan Earthquake (the quantified environmental impact is defined as the severity of environmental impact) and further, by incorporating a time scale, we discussed the appropriate disposal flow from both environmental economics and time axis viewpoints. As a result, it is shown that the promotion of broad-based disposal and reuse of waste is important from the comprehensive aspect of environmental impact and time.

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The solidification method including deep mixing stabilization is widely used as countermeasure of settlement of structures on soft ground and supplementary method for the construction of the structure. Recently, the technology that expects the reaction force from the solidification improvement ground is proposed in the highway bridge. To apply to an actual bridge, it is necessary to examine the bearing mechanism and the failure mode by the loading experiments and to examine how to secure the safety allowance against failure. In this research, bearing mechanism, reaction characteristics and failure mode pile foundation of highway bridge supported on contact column type cement-treated ground were clarified by lateral loading tests and numerical analysis. Based on demand performance of highway bridge foundation and acquired knowledge, what design and construction of pile foundation of highway bridge supported solidificated ground should be was considered.

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Pre-bored piling method using nodular pile (precast concrete pile) consists of pitching the nodular pile into soil cement formed by mixing and agitating cement slurry and soil. In pre-bored piling method, soil cement affects the vertical bearing capacity. Unconfined compressive strength of soil cement in base bulb is much larger compared to the deep mixing method. In this study, laboratory mixing test of soil cement in base bulb was carried out to clarify the characteristics of soil cement. From the examinational results, unconfined compressive strength of soil cement in base bulb is a good correlation between the effective cement-water ratio. It was found out that amount of gravel fraction and fine fraction content affects unconfined compressive strength of soil cement in base bulb.

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It is necessary to evaluate the slope stability considering the change of the ground water level on the slope surface layer for executing operation control more appropriately during wet weather. This paper has reported on a study conducted to develop a method for evaluating rain-induced slope failure and described the results of the study on the method of predicting the groundwater movement in the surface layer of the slope of interest by using a simple calculation method. In addition, the natural slope failure process is simulated with a simple predict model of the stability of slope surface layer. Specifically, decreased of a cohesion with increased of a degree of saturation are considered. The simulation results indicated that the observational result of slope failure time and location were good agreement with the calculated ones.

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Sudden failures of slope during or just after slope excavation works cause many serious accidents which sometimes take the lives of workers. Loss of lives and property damages could be prevented if early predictions of failure could be made. In this paper, some measurement apparatus was installed at the slope cutting site, and the installation performance of measurement apparatus, accuracy of measuring; long-term stability, etc. were checked. Although there is no special problem during construction phase, tilt-sensors installed near the slope cutting area showed a little deformation during slope cutting work. In addition, it is found that the slope creeps with some rainfalls event.

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A simple soil layer system which is composed of a finer soil (sand) layer underlain by a coarser soil (gravel) layer provides an excellent property of capillary barrier. The capillary barrier is necessary to make larger the gap of particle diameter of sand and gravel material. The functional deterioration of capillary barriers in service for dozens of years is of concern because of the transport of sand particles to the lower gravel layer due to an earthquake etc. The authors found that the inclusion of sand particles into the lower layer can be reduced by using the crushed shell particles instead of gravel in the capillary barrier. In this study, it’s examined an effect of the nonwoven fabric laying in the layer boundary surface to give to diversion length of the capillary barrier using a laboratory soil box test. As a result, the authors make clear not to have an effect of the nonwoven fabric laying to give to diversion length of the capillary barrier even if we laid it in the layer boundary surface.

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In order to resolve the existing problems regarding execution management and operational management, notably the management of structures built using the rock-bonding method for preventing rockfalls on a slope, an investigation was conducted to examine the effects of the construction, the earthquake resistance, and the overall state of such a structure. We found that a rockfall risk vibration assessment can be utilized to examine the effects of construction involving the rock-bonding method. We also observed that structures built using the rock-bonding method are resistant to earthquakes having seismic intensities slightly greater than 6 provided the results of the rockfall risk vibration assessment of such a structure are within a stable region. However, the result was guided by only two units of data, and thus improvement in the reliability of the result is desired. The consideration of these findings during the design and maintenance of structures constructed using the rock-bonding method, coupled with periodic maintenance checks can not only facilitate effective management of these structures but also extend the life of the structures.

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