open access

https://doi.org/10.14943/doctoral.k16357

https://hdl.handle.net/2115/95094

武甲山の残壁の掘削変位に与える弱層の影響と盛石の効果

英語

2025-03-25

Hokkaido University

xiii, 101p.

Unexplained rock slope deformation has been observed at the limestone quarry of Mt. Buko in Saitama Prefecture, Japan, since the automated polar system (APS) was introduced in the quarry. The rock slope in the western part shows significant and continuous deformation although little deformation has been observed in the eastern part. To restrain this continuous deformation, the construction of a stone wall was initiated on the west side. Ensuring the safety of the rock slope requires not only understanding the deformation mechanism but also evaluating the stone wall's effectiveness, which remains an urgent issue. Vertical and inclined weak rock zones were found through the quarry. The vertical one is developed in limestone deposit, and the inclined one is distributed along the geological boundary between bedrock and the cover rock, which is unexcavated limestone layer for the protection of the base rock against weathering. Understanding the impacts of these weak rock zones is expected to be key to clarifying the mechanism of rock slope deformation, as the connectivity of the two weak rock zones on the west side differs from that on the east side. Based on the aforementioned background, this study analyzed the deformation characteristics of the rock slope at Mt. Buko, focusing on the relationships among geological structures, excavation states, and field measurement data. Numerical models incorporating the quarry's geological features were developed to estimate mining-induced deformation of the rock slope, aiming to better understand deformation mechanisms. Both the constructed and planning stone walls at the quarry were also numerically modeled to evaluate their mechanical impacts and estimate their optimal dimensions. Furthermore, the effects of the dip angle and connectivity of the weak rock zones were investigated in detail for providing a generalized understanding of their influence. The effects of the stone wall height, width and construction timing were also examined. The specific contents of each chapter are as follows: Chapter 1 systematically describes the background, objectives, novelty, and importance of this study, along with a literature review of related research. Chapter 2 outlines the deformation issues, geological structures, mining history, and monitoring systems at Mt. Buko. The relationships between the characteristics of the rock slope deformation, the connectivity of the weak rock zones, and excavation progression were analyzed. The results show that rock slope displacement on the west side accelerates as the vertical weak rock zone (VZ) appears on the rock slope surface with the lowering of the excavation face. This finding emphasizes the importance of accurately modeling geological structures and excavation progress in analyzing deformation mechanisms. Chapter 3 presents numerical simulations of mining-induced deformation of the rock slope at Mt. Buko, with results that quantitatively align with field measurements. The models indicate the followings. A reduction in normal stress due to excavation leads to progressive failure along the geological boundary. Then, sliding force induced by the boundary failure applies to the VZ behind it. As the VZ appears on the rock slope surface, resistance against the sliding force decreases. Sliding movement stops as the excavation progresses, eventually reaching equilibrium. Thus, the observed continuous deformation is effectively explained by the proposed mechanism. Chapter 4 evaluates the effectiveness of stone walls at Mt. Buko by numerical simulation, highlighting its role in restraining slip deformation. The results reveal that the weight of the stone wall significantly influences the restraint of slip deformation. The mechanism of stone wall for restraining slip deformation is considered as not only increasing the bending stiffness of the area in front of the VZ, but also provides the press effect by self-weight, increasing the height of the stone wall helps to further stabilize the slope. Additionally, optimal dimensions for the stone wall were recommended for future construction. Chapter 5 numerically analyzes several effects of weak rock zone and stone walls by simplifying the geometry of rock slope and weak rock zones. It is found that no slip displacement is seen in models with single weak rock zone regardless of its dip direction. Slip displacement of a cover rock only occurs when two weak rock zones are connected. The slip displacement tends to decrease with increase of the thickness of cover rock. It is also found that earlier construction of a stone wall, up to higher elevations, provides the maximum deformation control. However, a critical value was found in stone wall height. No sliding can be seen at the critical height or more. These findings provide valuable insights for addressing similar issues in open-pit mines. Chapter 6 summarizes the main conclusions and recommendations of this study. A more in-depth analysis of the stone walls is necessary, as the effect of contact stiffness between the stone wall and the slope remain unclear. The lack of consideration for pore water pressure effects and three-dimensional factors are key limitations that could significantly impact slope stability.

2025-03-25

甲第16357号

博士(工学)

(主査) 特任教授 児玉 淳一, 特任教授 藤井 義明, 教授 川﨑 了, 准教授 福田 大祐

工学院（環境循環システム専攻）

博士論文

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