1/30-scaled static centrifuge model tests and an elastic FE analysis were conducted to investigate the seismic behavior of buried RC-pipe, FRPM-pipe and box-culvert. In the tests, distributions of normal and tangential earth pressures acting on the surfaces of the three types of model culverts, as well as those of bending strains produced in their walls were precisely measured during cyclic simple shear deformation of the model ground. Test results showed that the tangential earth pressures acting on the culverts were almost null in any case. Numerical results of the FE analysis in which slip and separation at the culvert-ground interface were allowed showed good agreement with the test results. However, the prediction from the current seismic design standard for buried sewer culverts using seismic deformation method based on spring model contradicted the test and numerical results in both earth pressure and bending moment distributions. An analysis using continuum models based on elastic theory clarified that the seismic deformation method has theoretical defects in predicting the earth pressure. Therefore, the FE method used in this study was proposed as a new seismic resistant design method of buried culverts. Earth pressure on and bending moment of the three types of the sewer culverts were calculated by both the proposed design method and the current design standard under the conditions specified in the design manual, confirming that these two methods generate considerably different results. The proposed design method considers the soil-structure interaction properly and simulates well both the test results and damage to buried culverts observed in the past earthquakes, while the current design standard does not. Therefore, the proposed design method is recommended to be used instead of the current design standard based on the problematical seismic deformation method.
In this study, we tried to evaluate the durability of wooden piles which have been applied to structure foundations and were constructed at approx. 100 years ago. The objective wooden piles have been located in sandy strata and above water table. In order to evaluate the durability, we conducted the visible confirmation of wooden pile surfaces, the soil investigations around wooden piles, and pilodyn tests. Furthermore, in order to confirm the strength and the bearing capacity, we conducted the uni-axial compressive tests of sampled wooden piles, the vertical compressive tests for cubic cut specimens of wooden piles, and vertical loading tests. According to these test results, we can confirm that the wooden piles are sound excluding approx. 1.5m from the pile head and good enough to have the strength and the bearing capacity to the design value set at the time of construction. The wooden piles have been above water table for more than 90 years, are made of pines whose water content is 45-80%. And the soil around them are sandy soil whose fine-grained fraction content is 15-25%, and natural water content is 20-30%. These results indicate that the wooden piles which have the similar characteristics and exist in similar conditions would not be severely deteriorated.
Recently, there is a possibility that vibration problems in areas near railways arise because of hastening of trains. When considering countermeasures against ground vibration, one must assess the frequency properties of the ground vibration and choose countermeasures that can reduce the vibration effectively in the predominant frequency band. In earlier studies, theoretical considerations and FEM analyses have demonstrated the vibration reduction effects using vibration-isolating groove or wall. However, we have insufficient knowledge to elucidate the mechanisms of wave propagation considering a vibration-isolating wall. Choosing a wall material with strong ground vibration reduction effects is also difficult. Therefore, we conducted model tests to assess countermeasures against ground vibration induced by a bullet train (Shinkansen). Experiment results showed that a vibration-isolating wall had stronger ground vibration reduction effects than countermeasures using weights located on the ground surface. Moreover, to display stronger ground vibration isolation effects, the rigid wall should be extended to the small ground vibration place without dividing small segments.
The investigation for producting the high strength solidified soils of 10 MN/m2 or more by mixing cement with dredged marine clay has been conducted. According to the results of the mix-proportion tests, in the case of Nagoya port clay, when the water cement ratio was set to 1.2 and the water content was set to 60 to 100%, the strength of 10 MN/m2 or more could be secured. In addition, in a production experiment of solidified soil block, a biaxial forced mixing mixer was used assuming construction on site. The constraint condition for producting a solidified soil block using this mixer was to secure fluidity for pushing out the treated soil from the opening of the mixer. As a result of fixing the water cement ratio to 1.2 and increasing the water content, it was possible to produce a solidified soil block at the water content of about 107% and the strength of core samples taken from the solidified soil block was 10 MN/m2 or more.
Aging and other such factors may cause ground anchors (hereinafter anchors) to deteriorate. When considering the construction of additional anchors, stability studies carried out at the initial construction of anchors will be valuable information. However, some early anchors have been in service for more than 40 years, and information available for designing and constructing countermeasures might be insufficient. In addition, the slide plane of a slope face where deforming has settled may be hard to estimate even after conducting boring explorations or movement observations. Furthermore, only the anchor head can be confirmed at the site since the most part of anchors is embedded in the ground. In such cases, setting the supporting strength, which decide the number of anchors to be installed, will be difficult when designing the additional anchors. This study proposes estimation method of slip surface for evaluation deterrent force of existing anchors from information gained by examining the appearance of the anchor head and other observations.
The ground anchor has been used as one of stabilizing technologies for cut slopes. The measurement of residual tensile force of ground anchor has been conventionally carried out by lift-off testing, however the development of a simple alternative tension measuring method is required in terms of cost and time. In this study, we have been continuously developing the application of a digital hammering technology using an acoustic emission sensor, which has been practically used as an anchor bolt inspection in nuclear power plants, etc. to the estimation of the tensile force of ground anchors. This paper shows our approach to evaluate and verify the applicability of the technology and to find out remaining tasks based on laboratory testing, finite element method (FEM) analyses and field inspection results in order to try to estimate the tensile force of ground anchor with the screw type anchorage device.
In Japan, there are approximately 30 to 40 slope failure accidents every year, causing injury to workers and damage to property. It has been reported that more than 50% of these accidents occurred during excavating or leveling the lower parts of the slope toe, indicating the necessity of developing a temporary and simple slope reinforced method to prevent such accidents during slope cutting works. Although many natural ground reinforced earth method for permanent have been developed to keep the stability of a steep cut slope, most of them are either difficult to set up under the construction or are too expensive to use at small to medium-sized slope cutting sites. In this study, as a simple and cost-effective slope reinforced method for small to medium-sized slope cutting sites, a temporary soil nailing was considered, and the reinforcing mechanism of soil nailing was investigated by centrifuge model tests. An in-flight excavator, which can excavate the model slope in high centrifuge acceleration environment, was used in this paper for simulating the slope cutting works. The deformation of mode slope during excavation was measured by PIV (Particle Image Velocimetry) and the deformation processes in the model slopes with and without the soil nailing were compared in the strain field.
Anticorrosion functions of ground anchors (hereinafter anchors) have been strengthened after the revision of standards by the former Japanese Society of Soil Mechanics and Foundation Engineering (present Japanese Geotechnical Society) in 1988. But some old-type anchors constructed before the revision fail to achieve the prescribed function due to corrosion of steel materials. Therefore, the three NEXCO companies have indicated in their expressway policy that they will install a new type of anchors in the special renewal and other works, which were approved in 2016. In installing additional anchors as a measure to supplement existing old anchors, some issues remain. For example, there is no concrete method developed to manage the tensile force when unloading tensile force of existing anchors. This paper examines the handling of existing anchors at the sites where special anchor renewal works were carried out, and based on the findings proposes a tensile force management method to be used in countermeasures for anchor deterioration.
It is essential to examine the evolution in hydraulic properties of rocks near high level radioactive geological disposal facility for evaluating the performance of the disposal system under thermal-hydraulic-mechanical-chemical coupled conditions. Especially, geochemical reactions such as pressure solution within fractures should be understood for predicting long-term permeability change of the rock masses. In this study, we have developed a novel THMC coupled model that can consider the pressure solution occurring at contacting asperities within factures predicted by damage theory. Using the developed model, long-term prediction of rock permeability was conducted for fictitious porous rocks that are assumed to be purely composed of quartz. The predictions show that a number of fractures are generated near the disposal cavity and permeability increases in damaged zone during the excavation, and after excavation the permeability of the damaged zone decreases to that of intact zone due to pressure solution at contacting asperities within fractures.
In recent years, the frequency of localized torrential rainfall is increasing, resulting in the occurrence of debris flow disasters that have a big influence on society. Since there are massive numbers of dangerous streams where debris flow is expected to occur, there is great significance in undertaking risk assessment, in order to implement efficient and effective countermeasures. It is very important to calculate the amount of sediment discharge and the movable sediment volume defined as the volume of unstable sediment, which are the basic factors in this evaluation. Additionally, it is crucial to estimate the erosion depth and width which are practical pieces of information. In this research, field surveys were carried out on 1,106 mountainous streams crossing the expressways in the Chugoku region. The distribution characteristics were evaluated based on a statistical analysis of the movable sediment volume, erosion depth and erosion width obtained in the field survey, and a standard value of the estimated erosion depth and width for calculating the amount of unstable sediment in dangerous mountain stream surveys was proposed.