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Estimation and prediction methods for hydraulic conductivity and deteriorated condition of vertical shafts by extended crack tensor theory

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Title
クラックテンソル理論を拡張した立坑の透水係数と劣化状態の推定ならびに予測手法に関する研究
Estimation and prediction methods for hydraulic conductivity and deteriorated condition of vertical shafts by extended crack tensor theory
Degree 博士(工学) Dissertation Number 創科博甲第99号 (2022-09-27)
Degree Grantors Yamaguchi University
[kakenhi]15501 grid.268397.1
Abstract
It is important to anticipate problems such as a large amount of spring water that occurs during shafts construction and maintenance problems such as concentration of lining cracks after shafts construction in advance, and to carry out construction in a rational manner. Crack tensor from the rock mass information (cracks, strength) obtained by the construction of the shafts of the Horonobe Underground Research Laboratory of the JAEA, aiming at the selection of support and the implementation of spring water countermeasures. Based on the theory, the research results were summarized with the aim of evaluating the water hydraulic conductivity of the rock mass during shafts construction and the deteriorated condition of the lining after shafts construction, and establishing a simple prediction method for these.
Chapter 1 summarizes the current state of rock mass geological observation and lining maintenance in the shafts, the water permeability coefficient of the rock mass, and the past domestic and overseas studies on the deterioration state of the lining, and the hydraulic conductivity of the rock mass using the rock mass information. The purpose of this study was clarified with the task of evaluating the deterioration state of the lining and establishing these simple prediction methods.
In Chapter 2, crack tensor theory and stereology (statistical geometry) are used using information (length, direction, opening width) of rock cracks during shafts construction. By applying the concept, the three-dimensional permeable tensor was estimated accurately. Then, when the hydraulic conductivity obtained from the three-dimensional hydraulic tensor and the hydraulic conductivity based on the result of the in-situ permeability test using the deep borehole near the shafts were compared, it was clarified that they were in good agreement. A high correlation was obtained between the crack frequency obtained by dividing the total length of the cracks obtained in the shafts construction by the evcavation surface area and the hydraulic conductivity obtained from the three-dimensional hydraulic tensor. Therefore, we
proposed a method to easily predict the hydraulic conductivity of rock from the frequency of cracks. The obtained prediction formula targets the depth at which three cross sections orthogonal to each other can be obtained on the rock crack observation surface, but the prediction formula was also obtained at a depth where three cross sections orthogonal to each other cannot be obtained. Comparing the hydraulic conductivity of the rock mass and the hydraulic conductivity based on the in-situ permeability test results, it was clarified that they are in good agreement.
In Chapter 3, the orientation dependence of the earth pressure is recognized in the underground environment of the Horonobe Underground Research Center, and it is the major principal stress direction in the shafts of the underground Laboratory. Cracks have occurred on the lining wall surface in the east-west direction. However, the lining cracks in the shafts at that point may depend not only on the orientation dependence of the ground pressure, but also on the rock cracks on the back surface of the lining, the ground cover and the rock strength. If a prediction formula for predicting lining deterioration can be created in consideration, it will be useful information for countermeasures during construction, and based on the crack tensor calculated based on the information on cracks, from the rock crack tensor and rock strength. I proposed a method to estimate the deterioration condition of the lining. The estimated value of the crack tensor regarding the deterioration of the lining using the obtained prediction formula and the measured value calculated from the information of the lining crack, assuming that the margin of error due to the relative error is 0.1, the estimated value and the measured value are well one. Im adei t clear that Ia md oing it.
In Chapter 4, aiming at selection of rational support for shafts extension of underground Research Laboratory planned in the future and implementation of spring water countermeasures. Ip roposed ac onstruction management system that applies the crack tensor prediction method for rock hydraulic conductivity during shafts construction and deterioration of lining after shafts construction. In the future, in order to select more rational support and implement measures against spring water, the rock mass information (cracks and rock mass strength) acquired during shafts construction will be obtained using the prediction formulas established in Chapters 2 and 3. By predicting the hydraulic conductivity of the rock and the crack tensor related to the deterioration of the lining, and reflecting it in the measures against spring water in the rock mass and the measures against the deformation of the lining, it can be expected to contribute to the reduction of maintenance costs.
Chapter 5 summarizes the research results in each chapter and raises future issues for conclusion.
Creators Yamasaki Masanao
Resource Type doctoral thesis
File Version Version of Record
Access Rights open access