Rockfall is an important geo-hazard of mountainous area in Japan and has gained greater attention and recognition due primarily to the severe accidents and mortalities happening in roadways and railways. Rock fall countermeasures are classified into preventive works and protectors. In rock protectors that have high rigidity, there are rock protecting fence, rock protecting wall and rock shed, etc. On the other hand, there is a pocket type rock net which excels in the application condition of the topography and absorbs energy by deforming itself. The standard absorbable energy of the pocket type rock net is 100 kJ. Then, the rock net is designed so that the absorbed energy exceeds the falling rock energy. However, in recently, many types of rock net such as high energy type and long span type have been developed, and there are cases where conventional design methods cannot be applied. In this study, the performance of a long span pocket type rock net was evaluated by dynamic analysis. Firstly, the physical properties of the rock net members were identified by comparing the results of the real scale field experiments with the dynamic analyses. Then, the relationships between the displacement of the net and the net width, the maximum tensional force of a horizontal rope and the rope position, etc. were evaluated by the dynamic analyses. Typically, these evaluations by conventional design methods are laborious and are carried out using the results of real scale field experiments. However, the current study revealed that the predictions by the dynamic, numerical analyses showed the validity of the performance evaluation by this means.
It is of significant importance to safely isolate the radioactive wastes from the human environments. Entombment of the wastes in deep subsurface may be a plausible solution on this issue, and will be adopted in the countries where the nuclear power plants are in operation. Before burying them in the targeted rocks, the longterm evolution of the mechanical and the hydraulic properties of the targeted rocks should be predicted with a certain precision. To this end, in this study we examined the change of the apparent secant elastic modulus and the permeability of a single fracture in the Berea sandstone and the Horonobe mudstone samples under the relatively high temperature and confining pressure conditions. The apparent secant elastic modulus of the mudstone increased with the increase of the holding time and specifically, the values at 90 ºC were greater than those at 25 ºC, while that of the sandstone little increased with time. In contrast, the permeability of both the mudstone and sandstone samples monotonically decreased with time, and the rates of the permeability reduction were close among all the samples. The increase of the elastic modulus and the decrease of the permeability may be attributed to the chemomechanical processes such as pressure solution and the mechanisms explaining the changes should be clarified. Although the mechanisms are still ambiguous, the increase of the elastic modulus and the permeability reduction with time may improve the integrity of the targeted rocks.
Transmission electron microscopy has been playing an important role in research and development of nanotechnology which is common and fundamental in various fields of science and technology such as energy, environmental sciences, information and telecommunications, and life sciences and etc. A transmission electron microscope (TEM) provides us with crystallographic information and positional information from a local area of specimen. Furthermore information on local chemical composition and atomic bonding state is obtained provided the TEM is equipped with an X-ray energy dispersive spectrometer (XEDS) and an electron energy loss spectrometer (EELS). The image resolution and special resolution of elemental analysis have been improved to an atomic level together with the development of an analytical TEM that has a field emission gun, an aberration corrector and a function of scanning TEM (STEM). It has been possible to extract high quality and various information on substance and materials, owing to the development of electron detectors and imaging techniques of STEM. Objects of TEM observation have been widely spread after the development of related techniques such as preparation of TEM samples and controlling of specimen environment (heating, cooling, gas pressure, stress application etc.). We introduce recent trend of transmission electron microscopy and demonstrate some applications to green nanotechnology which is closely related to development of renewable energy, energy saving, energy storing, saving of rear resource, removal of harmful substance from air and water and so on.