This is the summary for the paper (Iwano et al., 2020) receiving the best research paper award from the Japanese Society for Rock Mechanics (JSRM) in the fiscal year of 2021. In this study, for the purpose of environmental load reduction, blasting tests were conducted at a tunnel construction site using advanced electronic detonators in which arbitrary ignition times could be set. The test results showed that the peak amplitude of the vibration waveform from each of the blast holes follows the Weibull distribution. The superposition method proposed from these findings reproduced the vibration waveforms in delay blasting from the seed waveform recorded in single-shot blasting. The optimum delay interval determined accurately from the superposition method was almost equal to the one simply estimated from the method with the autocorrelation coefficient or a frequency analysis of the vibration waveform in single-shot blasting. These simple methods were validated at another tunnel construction site and found to be useful for estimating the optimum delay interval from single-shot blasting at each tunnel face on each day. This study is based on the practical consideration of actual tunnel blasting and construction, and these proposed methods will be widely applied to other tunnel construction sites.

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This article is a summary of the author’s thesis (LIU, 2020) which won the best doctoral thesis award from the Japanese Society for Rock Mechanics (JSRM). A coupled fracturing model including a fluid model and a solid model was developed to simulate supercritical fluids fracturing on a laboratory scale. The flow model and solid model are based on the pore-scale network method and the finite element method, respectively. The mechanisms of different performances between supercritical fluids and water-based fracturing on a laboratory scale are investigated. The simulation results were validated by comparing them with experimental results. Subsequently, an upscaling model based on the coupled fracturing model was developed to learn the supercritical water fracturing performance on the field scale.

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This paper is the summary of the paper by the authors (Hashimoto et al. 2021) receiving the best research paper award from the Japanese Society for Rock Mechanics (JSRM). Dynamic analyses of jointed rock masses, such as slope stability evaluations, have been intensively studied in recent years; discontinuous deformation analysis (DDA) is one of the feasible methods in this field. To predict the failure mode, the kinematic energy, and the reaching distance after the collapse, the friction characteristics of the rock joints must be computed correctly. The authors previously developed an improved DDA utilizing an implicit updating scheme of friction along the joints, the so-called return mapping method, which achieved higher accuracy and computational robustness for the dynamic sliding behaviors of rock joints than the conventional method. However, the improved method assumes that the joint friction angle is constant even after the joint fails as same as the original DDA, and this results in an underestimate of sliding displacement. Therefore, in this study, a simple transition algorithm from static to residual friction within the framework of the return mapping method is implemented to reproduce friction strength degradation. The performance of the proposed method is examined through the numerical examples and the improvements in the robustness, accuracy, and computational efficiency for the dynamic sliding problems along the rock joint were confirmed.

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