Strength characteristics of fine-grained soils at dyke slope surfaces

• 資料種別: 博士論文
• タイトル: Strength characteristics of fine-grained soils at dyke slope surfaces
• 著者・編者: Panta, Anand
• 著者標目: Panta, Anand
• 出版事項: Hokkaido University
• 出版年月日等: 2018-09-25
• 出版年（W3CDTF）: 2018-09-25
• 並列タイトル等: 堤防表層における細粒土の強度特性
• 寄与者: 西村, 聡; 石川, 達也; 渡部, 要一; 磯部, 公一; Nishimura, Satoshi; Ishikawa, Tatsuya; Watabe, Yoichi; Isobe, Koichi
• 授与機関名: 北海道大学
• 授与年月日: 2018-09-25
• 授与年月日（W3CDTF）: 2018-09-25
• 報告番号: 甲第13346号
• 学位: 博士(工学)
• 博論授与番号: 甲第13346号
• 本文の言語コード: eng
• NDC: 500
• 対象利用者: 一般
• 一般注記: Shallow slope instability poses challenging problem to the maintenance of many natural and engineered slopes, as triggered by heavy or incessant rainfall events, and the frequency of such events are predicted to increase due to the global climate change. For the shallow slope stability analysis of such earth structures, accurate characterization of soil strength at low effective stresses (5-20kPa), corresponding to soil failure at shallow depths of about 1-2m depth, is required. The accuracy of characterization of soil strength at the low effective stress, particularly in the fine-grained soils, is strongly dependent on capturing the characteristics of strength envelope with appropriate strength parameters, and how this is affected by soil structure and then potentially altered in field environment. In the first part of this study, the undrained strength behaviours of three fine-grained soils in natural (intact), reconstituted (intrinsic) and compacted states were investigated in laboratory to explore the characteristics of strength at low stresses. The studied fine-grained soils include two natural plastic clays, heavily overconsolidated Izumi clay and soft normally consolidated Atsuma clay, and a clay-sand mixed soil sampled from a river dyke construction site in Maizuru. The study focused on characterizing the state bounding surfaces of fine-grained soils by performing a series of constant-volume direct shear tests supplemented by hollow cylinder simple shear tests on Izumi clay, Atsuma clay and Maizuru clay-sand mixed soil in intact, reconstituted (intrinsic) and compacted states. Comparisons of non-linear bounding surfaces expressed by a power-law strength criterion for different states of clays suggested that the normalized strength and the degree of its non-linearity at intact states were higher than at the corresponding intrinsic states, probably due to inter-particle bonding as confirmed by the hollow cylinder simple shear tests. Whereas, the normalized compacted strength was significantly lower than the equivalent intrinsic strength, which was explained by meso-scale discontinuities in the compacted specimens by X-ray micro CT-Images. This difference was not significant in the clay-sand mixed soil. From these observations, it should be noted that the meso-structure in compacted clays is significantly different than that in more homogenous intact and reconstituted clays, and the conventional normalization based on the equivalent pressure concept does not capture it. In the second part, the study focused on characterizing the temporal and spatial variations in the near-surface strength of river dyke by taking a particular dyke site as example; Maizuru dyke, supplemented by limited data from Higashinosato dyke. Portable static/dynamic cone penetrometer tests were performed on a monthly basis in the year 2016/2017, and the results were interpreted with laboratory-compacted model ground penetration tests and consolidated-undrained triaxial tests. The surface strength of Maizuru river dyke increased gradually with depth showing small spatial and temporal variations in strength, and the strength was consistently found higher at a depth of about 0.4-0.5m from the surface than the Higashinosato river dyke and laboratory-compacted model ground, which were young and showed uniform strength along the depth. This may indicate that the Maizuru surface was subject to crusting (overconsolidation of clays as a result of desiccation) after a few cycles of seasons. The strength of soils from the studied dyke sites was characterized by following the approach discussed in the first part of this study, but with triaxial apparatus. Synthesis of the laboratory-measured strength parameters and the field-measured pore water pressure led to estimated field strength of the shallow layers. This surface strength and static portable cone penetrometer resistance exhibited a correlation consistent with lab-established one for 0.4-0.5m depth, but that for depth shallower than this was significantly different. A further study is necessary to endorse extending a simple, single-line correlation between the strength and cone penetrometer resistance to very shallow depth of compacted earth structure.; (主査) 准教授 西村 聡, 教授 石川 達也, 教授 渡部 要一, 准教授 磯部 公一; 工学院（環境フィールド工学専攻）
• DOI: 10.14943/doctoral.k13346; https://doi.org/10.14943/doctoral.k13346
• 国立国会図書館永続的識別子: info:ndljp/pid/11194650; https://dl.ndl.go.jp/pid/11194650
• コレクション（共通）: 障害者向け資料
• コレクション（障害者向け資料：レベル1）: テキストデータ
• コレクション（個別）: 国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文; https://dl.ndl.go.jp/collections/A00014
• 収集根拠: 博士論文（自動収集）
• 受理日（W3CDTF）: 2018-12-03T16:15:19+09:00
• 作成日（W3CDTF）: 2018-09
• 記録形式（IMT）: PDF
• オンライン閲覧公開範囲: 国立国会図書館内限定公開
• デジタル化資料送信: 図書館・個人送信対象外
• 遠隔複写可否（NDL）: 可
• 掲載誌（URI）: http://dx.doi.org/10.14943/doctoral.k13346; http://hdl.handle.net/2115/71822
• 参照（URI）: http://hdl.handle.net/2115/71821
• 連携機関・データベース: 国立国会図書館 : 国立国会図書館デジタルコレクション; https://dl.ndl.go.jp

• 要約等: Shallow slope instability poses challenging problem to the maintenance of many natural and engineered slopes, as triggered by heavy or incessant rainf...