Takao Yano

Improved digital photogrammetry technique for crack monitoring

Inspections to evaluate the safety, durability, and service life of aging infrastructure play an important role in determining the countermeasures that need to be taken, such as reinforcement, repair, and reconstruction. In infrastructure containing concrete, such as bridges and tunnels, crack widths and patterns on surfaces are two of the most important signs used to estimate durability. Current conventional techniques used for this purpose suffer from challenges such as tediousness, subjectivity, and high cost. Consequently, a new measurement technique that overcomes these challenges while measuring crack displacement with high accuracy and precision in aging civil engineering structures is needed. In this paper, we proposed a technique for measuring crack displacement using a digital camera image. In the proposed technique, reflective targets are established around both sides of a crack as gauges, and subsequent digital camera images of the targets are subjected to image processing to determine the displacements of the targets. These displacements can be measured using images captured from any arbitrary camera position. The results of experiments conducted to verify the efficacy of the proposed method show that crack displacements of less than 0.10mm can be measured with high accuracy and precision using digital images captured at a distance of 10.0m from the target, while less than 0.20mm changes in the tensile displacement of the crack can be measured from an image captured at 25.0m from the crack. Measurement results obtained from a tunnel are also presented to show that cracks in the walls of an actual tunnel can be identified through simple measurements. These measurements, taken over a period of one year, indicate that the tendency of crack displacement and slide movements are in close agreement.

Mechanical and hydraulic behavior of a rock fracture under shear deformation

With regard to crystalline rock that constitutes deep geology, attempts have been made to explore its hydraulic characteristics by focusing on the network of numerous fractures within. As the hydraulic characteristics of a rock are the accumulation of hydraulic characteristics of each fracture, it is necessary to develop the hydraulic model of a single fracture to predict the large-scale hydraulic behavior. To this end, a simultaneous permeability and shear test device is developed, and shear-flow coupling tests are conducted on specimens having fractures with varied levels of surface roughness in the constant normal stiffness conditions. The results show that the permeability characteristics in the relation between shear displacement and transmissivity change greatly at the point where the stress path reaches the Mohr-Coulomb failure curve. It is also found that there exists a range in which transmissivity is not proportional to the cube of mechanical aperture width, which seems to be because of the occurrence of channeling phenomenon at small mechanical aperture widths. This channeling flow disappears with increasing shear and is transformed into a uniform flow. We develop a simulation technique to evaluate the macroscopic permeability characteristics by the lattice gas cellular automaton method, considering the microstructure of fracture, namely the fracture surface roughness. With this technique, it is shown that the formation of the Hagen-Poiseuille flow is affected by the fracture microstructure under shear, which as a result determines the relationship between the mechanical aperture width and transmissivity.

Application of MEMS to monitoring system for natural disaster reduction

Recently it has become important to develop a new monitoring system for structures. This is because the ageing infrastructure and an increase in abnormal weathers caused by the climate change have resulted in hazard assessments becoming more difficult. Therefore, there is a need to be able to monitor vulnerable structures more carefully and to assess their safety in real time. For this purpose, we require a new monitoring system that can monitor a structure more closely, easily, and efficiently than the existing methods. We developed a new monitoring system using a Micro Electro Mechanical System and wireless communication. We applied this system to a retaining wall with a deep-seated slope failure, in order to assess the serviceability of this method in general, and the safety of this retaining wall in particular.

STUDY ON VARIOUS PROPERTIES CHANGE OF PERMEABLE PAVEMENTS WITH INFILTRATION OF RAIN WATER

The permeable pavements are mainly constructed for the purpose of cultivating ground water and mainly applied on the sidewalk. It was admitted that permeability was effective for flood which increases rapidly in the city. And application on a heavy traffic road is also considered now in regarding to a recent law about control runoff. Therefore, test constructions are tried in various places. However, it is necessary to solve problems, such as durability, to apply permeable pavements to the roadway. Especially, aggregates of granular materials moves by infiltration of rain water and the quality have been changed. This paper verified the quality change of granular materials by the infiltration of rain water.