Slope collapse triggered by snowmelt water occasionally occurs in snowy areas. The main purpose of this study is to develop a disaster warning system based on effective rainfall index added the analytical snowmelt estimated from a meteorological data such as a temperature. In this study, we verified the reasonable half-life parameters to be set for the effective rainfall index. As a result of comparing the groundwater level behavior of several slopes in heavy snowy area with the index, it was confirmed that a strong correlation is confirmed between them by setting the half-life parameters from 24 h to 96 h. And, as a result of case study using past disasters, it is suggested that effective rainfall with a half-life of 96 h can be appropriate index for a disaster alert system applied to embankments.

 A new method of non-destructive evaluation for residual tensile load of ground anchor has been developed. If the tendon tension part of a ground anchor is approximated by a “string” or “beam”, the frequency of its free vibration is determined by line density and tendon free length of the PC steel and the operating tension. Although the free vibration of tendon tension part cannot be directly excited because it is in the ground, it is confirmed by a physical model experiment that the free vibration can be excited by applying a power at the extra length of anchor head. A series of field experiments were conducted by using a small vibrator and an accelerometer. A swept-frequency vibration was applied to the extra length of anchor head, and the vibration wave form was measured at the same position. The observed wave form was analyzed by running-spectrum analysis in order to find a resonance frequency which is used to calculate the residual tension load.

 In recent years, the NATM method are often adopted for constructing a tunnel in the unconsolidated ground in urban areas. When encountering a highly permeable sandy layer, countermeasures such as sealing are required to control the groundwater. Depending on the type and amount of grout material used, however, the construction cost increases and the adverse influences on the groundwater environment may arise. With a goal to develop a new grout material, focusing on two types of Kaolin clay with different particle sizes produced in Okayama prefecture, Kaolin clay suspension was injected into a one-dimensional column filled with sand under a large hydraulic gradient and allowed one-dimensional infiltration. The results indicated that there was an optimum concentration leading to the most efficient permeability reduction. The mechanisms for the permeability reduction were investigated from the viewpoint of clogging characteristics during injection as well as the migration through the pores after injection.

 Precast L-type retaining walls installed on the road receives the wheel load of the passing vehicle with a product extension of 2m through the backfill because the products are not rigidly connected. In this study, firstly, lateral pressures acting on the wall through backfill was measured by repetitive loading experiments using the wall of a box made of light gauge steels. Secondly, pseudo L-type retaining walls were fabricated, and static destructive tests were performed on the stems. Based on the results obtained from static destructive tests and lateral pressures acting on the wall of light gauge steels, wheel loads at which pseudo-L-type retaining walls break under repetitive loading was estimated. Finally, repetitive loading tests were performed with wheel loads around the estimated failure load on pseudo L-type retaining wall. As a result, It was confirmed that the number of loads that the stem breaks through the backfill soil on the back of the pseudo L-type retaining wall changes depending on the magnitude of the repeated load.

 In evaluating the stability of natural slopes that have multiple layers with different soil strength, the safety factors obtained by slope stability analysis using a circular slip surface are not guaranteed to be the smallest safety factors, but the safety factor with non-circular slip surface can obtain reasonable slip surfaces with a smaller safety factor. This paper describes safety factor calculation of four slope models with simple or complex strata with a non-circular slip surface using the widely adopted particle swarm optimization method and a newly developed adaptive particle swarm optimization method. The proposed adaptive particle swarm optimization method is shown to be superior in terms of computational accuracy and speed.

 When the excavated rocks containing toxic natural origin elements are reused for banking or civil engineering materials, leaching test methodology is important issue to evaluate safety reuse. This study reevaluate the main leaching factors by using rock much containing arsenic generated by tunnel construction, and discussed the effective batch leaching method for excavated rocks to evaluate the long-term toxic risk. Arsenic leaching behavior using crushed fine-grained rocks is mainly controlled by secondly Fe/Al (hydro) oxide. The arsenic adsorption/desorption kinetic on Fe/Al (hydro)oxide and Ca compounds in alkali condition require weeks to attain full chemical equilibrium, and short-time evaluation have a non-matching risk with long-term leaching behavior.

 Maximum leaching concentration and available leaching volume are estimated by wet-dry leaching cycle, and the availability was proved it shorten the long-term higher-water/rock ratio reaction. Wet-dry leaching cycle is useful batch leaching test to evaluate the long-term environmental risk for excavated rocks.

 Large-scale submarine landslides can magnify the tsunami amplitude generated by earthquakes and cause severe damage to offshore infrastructures such as submarine cables and pipelines. It is, therefore, important to reveal the mechanism of submarine landslides and the kinematic behavior during the sliding process of submarine slopes. The authors, so far, have conducted laboratory model experiments to understand the kinematic characteristics of submarine landslides. It has been revealed that submarine landslide motions can be classified into three types based on the time histories of the slide velocity. In particular, in the case of the large landslide, it exhibited creep behavior in which the landslide velocity increased exponentially after a steady-state with the constant velocity. In the present study, we discuss those different types of landslide as a bifurcation problem from the steady-state slide and perform a linear stability analysis considering the nonlinear friction law. The main objective of this analysis is to find out the dominant parameters involved in the transition of the submarine landslide from the steady-state to the massive landslide. The results of the linear stability analysis show that the nonlinear system bifurcates into three cases depending on the change in the shear stress acting on the sliding surface after the onset of the slide: two stable cases and one unstable case. In particular, in cases where the system becomes unstable, it was found that the shear stress that is lower than that in the initial steady-state can lead to large landslides. Furthermore, time histories of the slide velocity and the displacement were calculated numerically for each case. The results showed that the slide velocity patterns observed in the experiments, and those calculated were well matched qualitatively. The results of the linear stability analysis mathematically support the idea proposed by the authors that submarine landslide behavior can be classified into three patterns.

 Numerous swelling pressure tests have been conducted to understand the swelling properties of bentonite which is planned to be used as a buffer material in repositories for the geological disposal of radioactive waste. In this study, in order to clarify the cause of the decrease in swelling pressure during the swelling pressure test period, the change in wet density distribution inside the specimen during the swelling pressure test was observed by X-ray CT measurement. It was supposed that this phenomenon was caused by the collapse inside the specimen. Furthermore, in order to confirm that collapse is generated by water absorption, the swelling deformation test was carried out under various load conditions. As a result, it was confirmed that collapse occurs even under the load conditions that are equal to or slightly smaller than the swelling pressure. These test data are expected to be used for validation of coupled analysis codes for evaluating the mechanical behavior of disposal facilities during re-saturation period.

 A simplified in-situ falling head permeability test was proposed by applying the Guelph Pressure Infiltrometer (GPI) method, which is an in-situ constant head permeability test for unsaturated soils. In this method, gravity infiltration is carried out from a single infiltration ring penetrated into the soil surface, and the behavior of the water level falling in the infiltration ring is automatically measured by a portable self-registering water level gauge. The field saturated hydraulic conductivity is calculated using the measured infiltration flow rate at the selected arbitrary infiltration head. In this study, the infiltration head and flow rate in the gravity seepage process which govern the accuracy of calculation of field saturated hydraulic conductivity and the applicability to the GPI method with two-head technique were investigated. The proposed method was applied to the unsaturated dune sands site and the slope of the first-class river levee, and was compared with the GPI method to confirm its usefulness and validity.

 The author proposed a method for theoretically calculating the interlayer distance of montmorillonite minerals, which are the main clay minerals, through experimental and theoretical studies on the water permeation phenomenon and swelling behavior of bentonite. By comparing the montmorillonite mineral interlayer distance calculated by this method with the size of the minute substance that is going to pass through the interlayer, it is possible to quantitatively evaluate the filtration ability of the montmorillonite mineral. In this study, the validity of this method was shown by quantitative evaluation of filtration of seawater components by montmorillonite minerals in the hydraulic conductivities of bentonite-based materials in an artificial seawater environment, and this method was used as the final industrial waste disposal. The author estimated the specifications of the clay-layer material that can be applied to the impermeable work in the field and can filter minute substances from biological waste, which has become an issue these days.