Traces of paleo-earthquakes, were found out at many archaeological sites, in Japanese Archipelago. Especially, traces of liquefaction have frequently found out during the excavation of the alluvial lowland, and the formation age was estimated by archaeological features and remains. Most remarkable features are dykes composed sand and gravel in which grains become finer approaching the surface. These traces sometimes make good the loss of the historical records, and useful for investigation about the history of great earthquakes, supposed to have occurred periodically along the Nankai trough. The estimated age of traces is sometimes corresponded to the date of historical earthquake, such as “Fushimi earthquake” occurred in 1596, and we can get concrete evidences about the ground disaster caused by the earthquake.

View full abstract

As a nondestructive investigation method of soil structure, the radar method was developed in this study. Although the ground penetrating radar has been used as a geophysical investigation, the method is not effective for the homogeneous soil structure. To improve the efficiency of the method, the concept of impact echo method for concrete structure was applied to the radar method. The newly developed method was verified for the laboratory test. Then, the field measurement was carried out for the embankment of irrigation tank. It was found that the proposed method was effective to examine the water content distribution and roughly location of water table.

View full abstract

In recent years, there has been a development of new construction methods to satisfy the river environmental conservation. In this study, a new method called reinforced river dike using geotextile is proposed as a new application of soil reinforcement technique. By using this method, it is possible to reduce the construction period and cost and to use vegetation on the slope. A real-scale field construction and field monitoring, full-scale destruction experiment, model experiment and numerical simulations have been conducted to establish design and construction methods for the proposed reinforced river dike. A manual with respect to design and construction is proposed based on these studies. In this paper, the design manual is reported.

View full abstract

To study effects of grain shape on mechanical behavior and shear band of glanular materials, a number of biaxial compression test were simulated with the DEM analysys, in which the specimens made by different types of grain shape were used. Each grain is composed of three particles which are overlapped each other. From these simulation results, it was found that the shear strengths obtained showed linear relation to the shape index “FU”, which characterizes grain shape. Besides, the rotations of grians contributed to the formation of shear band. A couple of shear bands appeared periodically, and the grain shape had effects on the quantities of grain rotation.

View full abstract

Surface displacement due to shallow inland earthquakes often causes damage to structures. A number of model tests were performed to examine the deformation of unconsolidated sediment subjected to fault displacement. In the case of strike-slip faults, the development of shear bands in subsurface layer has not been completely reproduced numerically, and the mechanism of surface fault rupturing has not been fully elucidated. In this study, DEM analysis was conducted to simulate model tests of strike-slip faulting. Development of shear bands and its mechanism were investigated. The analysis reproduced shear bands typical of strike slip faults; e.g. shear bands in the form of flower structures and en echelon Riedel shears. It was found that the development of flower structures and Riedel shears was attributable to the stress due to dilatancy and the shear in the vertical plane. The results also corroborated that secondary lower-angle shears developed under the stress field which Riedel shears reoriented.

View full abstract

In-situ permeability tests were conducted in peaty soft ground in Hokkaido and oedometer tests on undisturbed peat were performed, to investigate the permeability of peat and its anisotropy.
This study has revealed that the coefficient of permeability of peat from the oedometer test gives lower value of approximately 1/10 to 1/30, as compared with the results from the in-situ permeability tests, which indicate the average value of peat layer. The coefficient of permeability of peat and organic clay depends strongly on consolidation pressure and then “C_k” value increases with their initial void ratio or ignition loss. On the anisotropy of the permeability of peat, almost no dependency of consolidation pressure is found.

View full abstract

A novel stabilizing liquid using an air foam rather than bentonite clay slurry, i.e. an air foam suspension was employed in order to stabilize the trench wall surface during a diaphragm wall excavation. An air foam suspension is created by mixing excavated soil with air foam made from a surfactant. The performance of the air foam suspension depends on its density and consistency, that is, its table flow value (TF). By comparing the trench stabilization capacity of an air foam suspension with that of bentonite clay slurry in model tests, the performance of air foam suspension was confirmed. The performance of air foam suspension for diaphragm wall excavation is presented with two actual trial construction case records, which shows the superiority of air foam suspension to bentonite clay slurry as a stabilizing liquid. This method reduces the wasted soil volume produced from the diaphragm wall excavation and the construction costs of working on an underground diaphragm wall.

View full abstract

The Niigataken-Chuetsu Earthquake caused damage three fill-dam reservoirs of the Shinanogawa Hydroelectric Power Plant; this plant is owned by the East Japan Railway Company. Investigations were showed the settlement of the crest of the dam, cracks and sand pumping at the Shin-yamamoto Reservoir, one of the three reservoirs. The core showed no damage, and there was no damage that lost the function of dam. Therefore restoration was enabled despite the severity of the earthquake itself. However, the crest settlement of the dam amounted to as much as 2% of the height of the embankment.

View full abstract

The purpose of this research is the establishment of practical deformation analysis method for the improved ground by low replacement rate SCP method. Then, we examined physical and mechanical characteristics of the clay between sand piles. 1) Based on two offshore construction cases, we examined the time-dependent change of the clay by sand pile installation. 2) The sand pile installation process was reproduced in a triaxial cell and the behavior of the clay was examined at the element level. 3) The practical deformation analysis method for the SCP improved ground considering the stress history of the clay was shown and the applicability of proposal method was examined using the measured value.

View full abstract

Coral sand includes a lot of calcium carbonate. Colloidal silica contains phosphoric acid as a reactive material. Calcium carbonate reacts the chemistry with phosphoric acid included in colloidal silica, and carbon dioxide is generated. There were two problems by occasion of these. The first problem is that bubble with carbon dioxide remains in the improved sand, and strength of improved sand is not obtained. The second problem is that gel time shortens extremely and the grouting of colloidal silica into the ground becomes difficult. This paper describes the results of the laboratory tests of improved sand made by using coral sand, and the results of grouting test in coral sand ground. The laboratory tests have been conducted on improved sand such as unconfined compression and cyclic torsional tests. From the test results, it was found that: 1) improved sand by permeation grouting under constant confining pressure doesn't remain the bubble, and have enough strength; 2) colloidal silica can be grouting into the coral sand ground by colloidal silica gel time slows while flowing.

View full abstract

In the Tokyo International Airport (Haneda Airport), the new offshore expansion project with the fourth runway (D-runway) is being conducted. Undisturbed clay samples retrieved from the planned construction site were examined in the laboratory to evaluate their geotechnical properties. At the sandy layers, the standard penetration test was conducted to evaluate N-value. From the results of the site invesgitaiton, the stratigraphic model at the site was clarified. For the clay layers, a representative depth-profile for each soil parameter was determined by engineering judgement. In addition, the determined depth-profile was evaluated from a statistical point of view in association with the data variation.

View full abstract

This paper presents a tunnel deformation measurement technique by using digital images taken from a moving car. Because the three-dimensional coordinate of each target installed on tunnel wall can be calculated through photogrametric analysis, it is possible to obtain the positions of the pairs of targets whose distances represent the crown settlement and convergence. This paper summarized the results of experiments performed to verify measurement precision. As a result, the coordinate values of targets with a high degree of precison can be obtained from the geometric constraint conditions of the geodetic network without having to set any fiducial points. Based on this study, this paper argues the practicability of the proposed technique in the tunnel maintenance phase.

View full abstract

As is known, there are many fractures in rock slope, and these fractures are often the cause of failure. Especially, the mechanism of sliding failure depends on fractures in rock slope. In this paper, Three-dimensional numerical simulation for sliding failure by distinct element method are carried out. In relation to this simulation, the interparticle bonding force can be tried to be expressed by bonding theory. It is tried to be simulated an actual sliding failure of rock slope. As the results of this simulation, it is recognized that this simulation can be expressed on this sliding failure phenomena. Moreover, the process of sliding failure can be visualized.

View full abstract

This paper presents a first approximation of the elastic limit displacement of soil resistance to horizontally loaded piles. 37 field test data sets were consistently chosen from a vast database. Both mathematical and graphical approaches were adopted to interpret the elastic limit of soil resistance from the measured load-displacement curve. The data sets indicate that the mean value of the elastic limit displacement is 5% to 6% of the pile diameter, and its coefficient of variation is approximately 40% to 60%. A design horizontal threshold displacement can be also proposed as 2% to 4% of the pile diameter, considering the variation in elastic limit displacement.

View full abstract

Disposal facilities of low-level radioactive waste facilities underground use a sand-bentonite mixture as the buffer material. Tests have been performed to see if this mixture materials can be compacted on site. This sand-bentonite mixture is in an unsaturated condition and takes several decades to become saturated by underground water. A triaxial compression apparatus with variable suction control was used on the sand-bentonite mixture compacted with the optimum water content and maximum dry density to perform a net mean principal stress load, unloading test and shear test to investigate the effect of suction on the shear characteristics of the mixture. Suction minimizes the volume change in the sand-bentonite mixture as well as providing evidence of reductions in volume by unloading suction during the net mean principal stress load test. An greater suction was found to increase the shear strength and stiffness.

View full abstract

For predicting the air permeability coefficient from the water characteristic curve of unsaturated sandy and silty soils, the applicability of the air permeability model based on the Burdine theory and Mualem theory for expressing the relationship between the air permeability coefficient and the degree of water saturation is examined. As a result, the model based on the Burdine theory is more applicable during the drying process. However, the optimized parameter ξ-values for pore tortuosity in the models are varied for each soil and related the shape of the water characteristic curve. And then, it is recognized that the both models are good agreement with each other and fitted to the measured air permeability coefficient.

View full abstract

Liquefaction resistance of soil dramatically increases with decreasing degree of saturation (S_r). This paper proposed a technique for preparing fully saturated model ground used for centrifuge tests. The technique was verified through a series of test on sands with different grain size. It was found that the air entrapped in the funicular saturation zone during the saturation process degrades degree of saturation. The high degree of saturation can be achieved by applying centrifugal acceralation during the process. The saturation process in centrifuge with an aid of vaccume pressure achieved S_r of 99.3% for sand with considerable amount of fines. A technique of high accuracy measurement of S_r is also developed.

View full abstract

Japan Atomic Energy Agency has been conducting the Horonobe Underground Research Laboratory (URL) project in Horonobe, Hokkaido, as a part of the research and development program on geological disposal of high-level radioactive waste. This paper shows the synthesis results of hydrogeological investigations in the surface-based investigation phase of the project. Hydrological and meteorological investigations show that the infiltration rates of the drainage basins depend on the flora and the topography. The hydraulic tests using the deep boreholes reveals that hydraulic conductivity of the in situ test scale varies widely and decreases with depth in the same formation and that of laboratory test scale is influenced by the stress history. The groundwater flow analysis based on the investigations shows that the groundwater flows over topographic watershed and that the groundwater pressure is kept high in the deep underground.

View full abstract

One problem has usually arisen that earth-pressure sensor causes stress concentration in the earth. A new type of earth-pressure sensor with low-rigidity is invented, which is based on the idea to devise effective means of making the apparent-rigidity of sensor the same low as earth. Furthermore, a triaxial variable air-pressure calibration system is newly developed. The test results show that comparing with the diaphragm-type sensor, the measurements gained using the developed sensor are nearer to the real ones. The properties of output error and hysteresis of the sensor that are not given by the error theory about traditional types of sensor are obtained, which benefit the development of optimum earth-pressure sensor.

View full abstract

The excavation of a mountain tunnel through the unstable ground requires full use of techniques or resources. In a mountain tunneling process, various auxiliary methods are in practice for controlling the damage of surrounding environment and ensuring the safety of construction sites. A steel pipe fore-pilling (AGF method) and a vertical pre-reinforcement method are often employed for ground settlement control. Although both methods are well known as effective methods, they have not been evaluated clearly for their control effects. In this article, the investigation of settlement control effects was examined by using displacement data obtained during construction. The effects were evaluated by using a finite element method (FEM) and it was proved that, for the displacement control in the similar type of ground, the vertical pre-reinforcement method was more effective than the AGF method.

View full abstract

The field test of earthfill, which consists of Hachinohe Shirasu and Tsukidate soil, were carried out to study the seepage behavior due to rainfall and evapotranspiratin behaviour after rainfall. By installing the dielectric aquameter sensors and tensiometers in the earthfill, the soil water content and the suction were continuously measured from July 2004 to Decsember 2006. We clarified the rlationsip between rainfall pattern and increasing property of water content due to rainfall and the change of seepage and evapotranspiration behavior from year to year. Furthermore comparing hydraulic property which acquired from field monitoring tests considering hysteresis with laboratory one, it was concluded that the field monitoring results agreed with laboratory test results.

View full abstract

The compaction grouting method is used for soil foundations beneath existing structures as liquefaction countermeasures. It improves the ground by injecting mortar into the ground with high pressure. However, heaving or stress change, which affects the existing structures, may be caused in the grounds by the injection. Model tests on the compaction grouting method were conducted in order to investigate the soil behaviors. In the tests, its execution procedures were simulated on model grounds. Shaking table tests were, also, conducted after the execution. This paper describes the model test results and some discussions on the similitude of the model test for the predictions of ground behaviors during actual executions.

View full abstract

One-dimensional consolidation analysis is described for predicting the consolidation time curve of clays exhibiting secondary compression during primary consolidation. The constitutive soil model is based on the equation governing the secondary compression rate of the decrease in void ratio. This model uses four parameters, C_c, C_c^*, C_α and c_ν^* that can be easily determined or assumed from the conventional standard oedometer test results. As a check on the validity of the proposed soil model, the consolidation time curves observed in oedometer specimens are compared with those predicted by the analysis. Satisfactory agreement can be obtained between the computed behavior and oedometer observations. In adition, it is shown that the void ratio rate due to secondary compression during primary consolidation varies to about two degits as much as its final value before the application of the next loading increment.

View full abstract

The objective of this study is to evaluate the effect of freeze-thaw sequence on the mechanical behavior of crushable volcanic coarse-grained soils. A new test apparatus, which can simulate freeze-thaw sequence in real foundations, was developed and a series of triaxial compression tests and water retention tests were performed. Test results showed that the freeze-thaw sequence made the amount of particle breakage increase, and as the result its strength decreases and water retention capacity increases by being exposed to freeze-thaw action. This indicates that the freeze-thaw action has strong influences on the mechanical behavior of crushable volcanic soils even if the soil lacks in frost heave characteristics.

View full abstract