We proposed high-viscosity fluid injection tests to evaluate flow dimension and porosity in fractures. Experiments were conducted to evaluate the method by injecting high-viscosity methylcellulose solution at a constant rate into stainless steel tubing and model fractures. In stainless steel tube experiments, injection pressure increased linearly with time and the pressure gradient was dependent on tube diameter. In model fractures, injection pressure increased logarithmically with time and the pressure gradient was controlled by fracture width. Changes of tube diameter and fracture width could be estimated from the derivative of the pressure. High-viscosity fluid injection tests were able to identify the flow dimension (e. g. one- and two-dimensional flow) and quantify features controlling porosity, such as tube diameter and fracture width. Our results confirm the applicability of high-viscosity fluid injection tests to determine fracture properties in laboratory experiments.
To increase the sliding resistance of a caisson type breakwater against wave force, it is effective to provide back-filling behind the caisson. In this paper, a solidification soil was used as back-filling behind the caisson, and its effect was evaluated by a centrifuge model test. According to the test results, it was confirmed that the sliding resistance increased by back-filling of solidification soil was consist of two components, i.e., one is the shear resistance of the solidification soil and the other is the frictional resistance between the solidification soil and the sand foundation at the bottom of the solidification soil. Therefore, to increase the sliding resistance in drastic, it is considered to be effective that the strength of solidification soil is increased and the prevention works are constructed for preventing the solidification soil from sliding on the sand foundation.
The purpose of this study is to clarify the relationships between incoming angle and coefficients of restitution, friction coefficient, rotational motions, and energy ratio for spherical boulder impacting on rock plate. In this paper, the parameters for spherical boulder impacting on rock plate will be presented based on our experimental data by free-fall-rebounding laboratory experiment using high-speed video camera system. Furthermore, this paper explains influence of combination of normal and tangential components of coefficients of restitution for numerical analysis on rockfall motion. As the experiment results, the incoming angle is one of the factors that greatly affect the value of tangential component of coefficients of restitution. The normal and tangential components of coefficients of restitution are closely related to energies after impact. The result of numerical analysis showed that the increasing trend of the tangential component of coefficients of restitution can be modeled with spring-dashpot-slider system.
Given that Japan has a great deal of slopes with geographical steepness and geological weakness, the idea of preventive maintenance has been employed in the aim of securing the safety and strength of our land against natural disasters. From the preventive maintenance point of view, the quantity of slope inspections is expected to increase, since stable slopes where no movement is presently observed require inspection in order to grasp the current danger of collapse. Especially in the Chugoku region where local severe rain is increasing, there are many slopes with potential risks, which make the preventative maintenance against landslide disasters more important. In this research, the singularity of the relationship between the disaster history of highway slopes and the geography, geology, and rainfall, is derived by analyzing the surface geology from the perspective of the preventive maintenance against road disasters.
Finite element models of specimens which imitated rock slopes were made to validate applying the hammering method on the stability estimation of rock blocks. At first, transient response analysis was done. We confirmed validity of analysis models because the sound pressure spectrums were most of the same with the velocity spectrums. Next, modal analysis were done, we studied about the vibrating situation of the specimens in the experiment. As the result, it was shown that we could recognize vibrating situation that concerned the stability of the rock blocks by hammering method. And it was shown that we could apply hammering method on the quantitative stability estimation of rock blocks. In addition, transient response analysis was done for recognizing the influence on the difference of the size of the rock blocks and the modulus of direct elasticity. As the result, the difference of them influenced on the result of the hammering method, the result showed the difference of the stability of the rock blocks. In the end, we measured the sound pressure spectrums at the real rock slopes. We confirmed that it is possible to comprehend the rock stability by hammering method.
In the freezing method, frozen soil wall to endure earth pressure and hydraulic pressure is made by installing freezing pipes near the underground constructions such as shaft. After creating the frozen soil wall, a partial temperature rise or thawing of the frozen soil may occur due to the heat of excavation or of gas cutting of steel. In addition, the suspension of circulation of coolant to the freezing pipes or the change of temperature may take place in order to control the creation of the frozen soil wall. In general, the shape of the frozen soil wall created by this method is complicated, and because heat conditions change with time, it is important to predict in advance things like the range of frozen area and temperature distribution over time. Consequently, we introduce three-dimensional nonsteady heat conduction analysis based on differential equations, and explain the differential equations and boundary conditions in this paper. We confirm the validity of this method by the comparison with the measured values of the construction site and the analytic values. Also we present the results of model analysis envisioning the underground connection of shield tunnels in order to evaluate the effect of heat transfer on a frozen soil wall.
The coefficient of earth pressure at rest is obviously important in geotechnical problems. The influence of a new plastic potential on the minor principal effective stress during one-dimensional consolidation is examined by finite element analysis. Results of experimental and numerical investigation indicate that the coefficient of earth pressure at rest K0 during one-dimensional consolidation appears to be governed by the plastic potential and secondary compression time effects.