This article summarizes the authors’ studies on a high-precision simulator for hydraulic percussion rock drills, which received a technical award from the Japanese Society for Rock Mechanics in the fiscal year of 2016. Hydraulic percussion rock drills are widely used for blast hole drilling in mines, quarries, and tunnel construction sites. The performance and efficiency of rock drills affect the time and expense necessary for rock excavation, and therefore advancement in rock drills has been required. The design and development of rock drills based on experimental results require much time and effort. Alternatively, computer simulation is an effective method, but the computational models in previous studies were too simple to implement recent rock drill mechanisms. In a series of studies by the authors, precise computational models for stress wave propagation, bit penetration into rock, and the behavior of a rock drill body were proposed based on experimental results. A high-precision simulator for hydraulic percussion rock drills was then constructed by combining the proposed component models. The simulator was able to precisely reproduce consecutive percussive drilling into granite with a rock drill.

View full abstract

This article is the summary for the thesis (Liu, 2016) receiving the best doctoral thesis award from the Japanese Society for Rock Mechanics (JSRM) in the fiscal year of 2016. First, a review study is presented to introduce previous studies on estimating permeability of discrete fracture networks. Mathematical expressions of permeability are summarized with the geometric properties, including: fracture length distribution, aperture distribution, fracture surface roughness, fracture dead-end, number of intersections, hydraulic gradient, boundary stress, anisotropy, and scale. Second, high-precision fluid flow tests and numerical simulations by solving the Navier-Stokes equations are conducted to investigate the nonlinear flow properties of fluid in both intersections and fracture networks. The results show that with the increment of the hydraulic gradient, the ratio of flow rate to hydraulic gradient decreases. When taking account of fracture surface roughness, the ratio of flow rate to hydraulic gradient would reduce by 0 - 26.55%. Finally, the fractal properties of rock fracture networks are characterized and a fractal model is proposed to link the fractal characteristics with the equivalent permeability of the fracture networks. The fractal dimension DT that represents the tortuosity of the fluid flow and another fractal dimension Df that represents the geometric distribution of fractures in the networks, are introduced into the model. The results indicate that compared with the parallel plate model, the maximum deviation of the calculated flow volume that considers the effect of tortuosity can be as high as 19.51%. A multiple fractal model for estimating the permeability of dual-porosity media is proposed. Analytical expressions for the fractal aperture distribution, the total flow rate, the total equivalent permeability, and the dimensionless permeability are derived. Thus the permeability of fractured rock masses could be easily assessed using the proposed method as a first order estimation.

View full abstract

This article is the summary of the published paper (Nishimoto et al., 2016). The objective of this study was to evaluate the long-term behavior of a deep geological repository for high level radioactive waste disposal, using the centrifugal near-field model test. The model consisted of a sedimentary rock mass, bentonite buffer, and model overpack, and was enclosed within a pressure vessel. Tests were conducted with a centrifugal force field of 30 G under isotropic stress-constraint conditions with confining pressures of 5 to 10 MPa and injection of pore water up through a time period equivalent to about 165 yr in the field. Our results showed that the measured values and the temporal changes in the displacement of the overpack, the soil pressure of the bentonite, and the strain of the rock mass were clearly dependent on the confining pressure. These data were not convergent during the test. Our data experimentally revealed that long-term behavior in the near-field was changed by the geomechanical interaction between the deformation stress of the bedrock/disposal hole and the swelling behavior of the bentonite buffer.

View full abstract

In bedrock construction projects such as dams and tunnels, it is important to have a detailed grasp of the geological structure at the project site and to perform planning and construction appropriate to the situation. To that end, in recent years there have been investigations of various construction information modeling (CIM) management methods that realize 3D modeling of the presumed geological situation and the results of actual geographic observations. This paper describes the creation of a construction site support system for geological risk, in particular issues related to geological information CIM management system development, system content, and application to actual tunnel and dam excavation projects.

View full abstract