The reinforced earth walls have come into wide use in Japan after 1995 Hyogo-ken Nanbu Earthquake in particular. High seismic resistance of the reinforced earth walls has been shown by the large earthquakes occurring in Japan, e.g., the 2011 off the Pacific coast of Tohoku Earthquake and the 2016 Kumamoto earthquake. However, a reinforcing mechanism of the seismic resistance regarding to the reinforced earth walls has been clarified insufficiently. The authors have developed the new reinforced earth wall using the reinforcement member incorporating both a friction resistance and a bearing resistance. A prototype reinforced earth wall was constructed in Sendai City after the Tohoku Earthquake, and then, dynamic and long-term static data in the reinforced earth wall had been measured for three years. In the present paper, the observed dynamic behavior of the proposed reinforcing member during the relative large two aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake are shown. Both a bearing resistance and a friction resistance were separately measured in a reinforced member during the aftershocks. The bearing resistance and the friction resistance acted effectively in the reinforced member at shallow and deep positions, respectively.
Monitoring of soil moisture and groundwater level is important for predicting slope failure caused by heavy rainfall. We have been developing a new device using ultrasonic waves for monitoring soil moisture and groundwater level. In this paper, threshold level has been validated for prediction of slope failure using the reflective intensity and the propagation time which obtained by ultrasonic measuring system by slope collapse experiment using a full scale model. As a result, ultrasonic measuring system can detect quasi-saturated state, saturated state of soil, and rise of groundwater level, are warning signal of collapse.
The 2011 off-the Pacific coast of Tohoku earthquake affected Japan, wreaking severe damage to a nuclear power plant in Fukushima. During decommissioning, ensuring worker safety is important in relation to fuel debris retrieval. Given that background, the authors specifically examined the use of heavy bentonite-based slurry as a filling material in a nuclear reactor. Heavy slurry can shield gamma rays and neutron beams because of its high specific gravity and water contents. Also, soil materials are used for soil cover type storage facilities for radioactive waste without evaluation for shielding. This research was conducted to investigate and define the radiation shielding capability of soil materials for controlling nuclear accidents. To quantify the radiation shielding capability, the authors measured the transmitted radiation dose through soil materials under some conditions of pass length. Results show that the reduction of the gamma ray dose has a proportional relation with wet density of materials, and show that the reduction of the neutron beam dose is related with the volume water content of materials. The research described in this paper is a proposal for application to the design for construction using soils for decommissioning of the Fukushima Daiichi Nuclear Power Station.
In order to predict the time of slope failure during an excavation, a full-scale model slope was built, and the deformation of the slope surface was monitored during slope excavation. The surface displacement rapidly increased with the elapsed time after the excavation, and the relationship between the displacement and elapsed time included an exponential function just before collapse. Based on the results, by computing the inverse of the velocity of the slope surface displacement, a warning signal can be provided 7 min before collapse. In addition, we determined that this method can apply to the data obtained by extensometer, distortion meter, and clinometer.
The decorated burial chambers in tumuli have been deteriorated due to temperature change and moisture movement in the burial chambers. Heat insulation of a burial chamber by covering with an earth mound is one of feasible means to control the damage. In the present paper, the temperature and dew condensation in a burial chamber was evaluated by one dimensional equation of heat conduction to investigate the influence of the thickness, degree of saturation and dry density of the mound on the chamber environment. The calculated performance suggested that the thickness of the mound has larger influence on the environment in the burial chamber than other factors. Therefore, the thickness of the mound is a key factor for designing an earth mound storing a decorated chamber which requires hydrothermal environment control for preservation. On the other hand, the degree of saturation and dry density of the earth mound with less influence on chamber environment should be decided considering the mechanical stability and water infiltration of the mound.
An equivalent linearization analysis based on the elastic beam foundation theory has frequently been used on actual structural foundation designs. The deformation modulus of soil, which is defined as the secant incline in the stress-strain relationship, is the most important parameter on an equivalent linearization analysis. Specifically, the deformation modulus of soil should be adjusted in accordance with the deformation level of the foundations and the strain level of the soil. In this study, theoretical approaches were conducted with regard to the relationship and consistency between primary soil investigations. Furthermore, strain dependence modeling for the modulus of soil has been considered via a statistical approach using a large-scale soil investigation database conducted at bridge construction sites. From the above considerations, a practical estimation method to evaluate the rational deformation modulus of soil is presented based on soil investigations and SPT-N values.
An equivalent linearization analysis based on the elastic beam foundation theory, i.e. spring model, has frequently been used on actual structural foundation designs. A method to convert the nonlinear properties of soil to an equivalent linear model in order to conduct rational calculations is required. The purpose of this study was to examine whether the relationship between the soil strain level and structural deformation level can be used to simplify the model from applicability to actual structural design. From the results, a versatile scheme to set the rational modulus of a subgrade reaction in various structural deformation levels was presented with consideration for the relationship between the structural deformation level and soil strain level.
At the 2011 off the Pacific coast of Tohoku earthquake, hinge-type arch culverts experienced the large damage which led to loose the transport availability for the first time. The resultant disaster seems to be closely related to the inertial force in the culvert longitudinal direction. These damaged culverts had one point in common, namely, the small soil cover of the culverts or the embankment slope began very near the mouth wall. Therefore, the aim of this study is to clarify the influence of the embankment shape on the seismic behavior of precast arch culverts in the culvert longitudinal direction. We performed dynamic centrifuge tests on an embankment model including precast arch culverts with the change of embankment shape patterns. As a result we found that in the case of the culverts with small soil cover, the seismic behaviour of the culverts near the mouth with the smallest constraining effect of embankment get to be amplified largely and exceeds that of the surrounding embankment, and that in the case of the culverts with large soil cover, the seismic behaviour of the surrounding embankment strongly binds that of the culverts near the mouth, which leads to the united response between the culverts near the mouth and the surrounding embankment.
The Fukui earthquake in 1948 caused extensive damages of river levees. Further, deformed levees by earthquake greatly caught the influence of external force by high water with rainfall. In this study, we investigated seepage behaviour of deformed levees after shaking and evaluated durability of deformed levee under plural external forces such as earthquake and high water using centrifugal model tests. As a result, the flux through the deformed levees with shaking was larger than that through non-deformed levee without shaking during high water, and progressive seepage failure was observed near the cracks on levee slope after shaking.
In seepage flow analyses employing the finite element method, recharge or pumping wells are generally approximated by point sources, since the wells are extremely small compared to the analysis region or other subsurface structures. However, such wells, when modeled as point sources, often yield inaccurate results. The authors have developed a new well model using point sources that improves the solution accuracy. This well model calibrates the permeability of finite elements surrounding the point sources based on theoretical solutions. The effectiveness of the well model has been presented via several numerical experiments in published papers. This paper discusses the outcomes of code verification on the present well model in Verification and Validation (V&V) terms.
Ground anchors are installed in general in slope, and it is useful to maintain the stability of the slope. Anchors is constructed in heterogeneous ground, therefore, the residual tensile load and the function of the anchor tendon show different changes at each anchor. Currently, there is the method for evaluating the health level of the anchor based on lift-off test result. However, there is not defined the method for evaluating the health level of the anchor slope. In this paper, we conducted many lift-off tests on cut slopes, and proposed the health evaluating method of anchors slope that based on the variation in the function of anchor tendon and the incidence of failure anchor.
In order to improve a dredged clayey ground, the vacuum consolidation method (VCM) using horizontal drains has been developed and already effectively applied at 10 construction sites. In this consolidation method, the drains are horizontally installed in the very soft clayey ground using a drain installation ship, and a negative pressure was applied to the clay through the horizontal drains. In case of the VCM using vertical drains, the drains with 0.1 m in width and 0.003 m in thickness were usually used. On the other hand, the special prefabricated drains were used in case of the VCM using horizontal drains, where its dimensions were 0.15 m in width, 0.01 m in thickness and 250 m in length. Wide and thick drains bring an advantage to prevent the delay of consolidation when long drains are used, because the well-resistance of drains is small. In this paper, the design, the execution procedure and the four case histories regarding the VCM using horizontal drains are generally described from outcomes of the former study.