臺灣博碩士論文加值系統

一般砂質土壤明挖邊坡之潛在破壞面存在負孔隙壓力，使砂土之基質吸力提供外視凝聚力，使邊坡不會在剛開挖時發生破壞。但當土壤飽和度降低到零，負孔隙壓力一定消散到零，則邊坡一定發生崩塌。故維持明挖邊坡土壤之飽和度，即為維持砂土邊坡不崩塌的重要條件。
本研究以階段式開挖及鋼絲網噴凝土護坡封層，保持切坡下土壤之飽和度，使切坡後之負孔隙水壓及毛細應力不消散，用以維持邊坡潛在破壞面在開挖期間之外視凝聚力，而不發生崩塌及保持砂土切坡為楔形破壞，並因護坡殼使砂土切坡後飽和度不變，維持開挖解壓後之負孔隙壓力不排水，即強制砂土在開挖期間屬於短期強度應力行為。本研究護坡封層範圍超過潛在破壞面2m以上，維持砂土邊坡潛在破壞面內之飽和度，在無地震下完成開挖深度5.5m之70°、60°、55°砂土邊坡，配合切坡上傾斜變位計管之邊坡側向變位量測值及STEDWin2.7、RISS電腦程式分析邊坡之安全係數，成功印證階段式開挖配合鋼絲網噴凝土護坡封層之砂土明挖技術之可行性及經濟性。比較相同規模之開挖，本工法成本約為連續壁工法之1/6，排樁工法之1/3，鋼板樁工法之1/2。土釘式護坡明挖技術，更能安全與省腹地空間在砂土地盤進行明挖工程。
本基地砂土地盤垂直開挖之寬度B與深度D之比值B/D>0.37，砂土即無角隅之拱作用行為。本砂土護坡式開挖工法，建議安全係數取1.2以上，切坡角度以60°至75°之間較實際。

Based on the negative pore pressure, the potential failure surface can provide a useful apparent cohesion force to stabilize the slope during open-cut excavation.While saturation degree of the sandy soil is reduced to zero, the negative pore pressure does not exist anymore and the slope could collapse.Thus, maintaining fully saturated sandy soil condition will make the slope safety.

The aim of this study is to explore the influence on slope stability from saturation degree of the soil. In a full-scale test, a stage excavation without any lateral support was carried and the steel-mesh shotcrete was used to cover the excavation level and slope face. In this test, the final excavation depth is 5.5m but three different slope angle, 55°, 60° and 70° are considered for the stage excavation.For such cases, the influence of earthquake is not consider. The negative pore pressure and saturation degree of the soil are expected to be remained after shotcrete covered and the sand would behave undrained in this way. After leaving for 31 days, the shotcrete face will be removed immediately before the start of next stage excavation and the sample of soil from the slope will be tested for its saturation degree. Also, several inclinometers were installed in the slope to measure the deformations after the removal of shotcrete.

Apart from the field test, the numerical simulation using the computer program STEDWin 2.7 and RISS was carried out to predict the performance of slope. Based on the outcome of this study, it is concluded that the use of stage excavation with steel-mesh shotcrete face in the excavation is acceptable and economical. Comparing the same scale of excavation, the total construction cost of this method is approximately 1/6 of the use of diaphragm wall, 1/3 of the use of soil mixing wall and 1/2 of the use of sheet pile wall. Using the soil nailing with method can even save space during the excavation.

There will be no corner effect for an excavation in sand in which the ratio of the excavation width (B) to the excavation depth (D) is more than 0.37 (B/D>0.37) based on observations from this site.For design of the open-cut using such face protection measure, it is suggested that safety factor need to be at least 1.2 and angle of cut slope should vary from 60° to 75°.

中文摘要 -------------------------------------------------------------------------- i
英文摘要 -------------------------------------------------------------------------- ii
誌謝 -------------------------------------------------------------------------- iv
目錄 -------------------------------------------------------------------------- v
表目錄 -------------------------------------------------------------------------- viii
圖目錄 -------------------------------------------------------------------------- ix
照片目錄 -------------------------------------------------------------------------- xiii
符號說明 -------------------------------------------------------------------------- xvi
第一章 緒論-------------------------------------------------------------------- 1
1.1 研究背景-------------------------------------------------------------- 1
1.2 研究目的-------------------------------------------------------------- 1
1.3 研究方法-------------------------------------------------------------- 2
第二章 前人研究-------------------------------------------------------------- 4
2.1 砂土明挖作業之開挖面高度及坡度----------------------------- 4
2.2 垂直明挖臨界高度分析-------------------------------------------- 4
2.3 砂土無限邊坡分析-------------------------------------------------- 5
2.4 負孔隙壓力----------------------------------------------------------- 6
2.4.1 不飽和砂土基質吸力----------------------------------------------- 7
2.4.2 土壤中毛細管水揚升之負水壓----------------------------------- 9
2.4.3 開挖解壓之負孔隙壓力-------------------------------------------- 11
2.5 相關工程案例-------------------------------------------------------- 12
2.5.1 基地一：中國大陸南陽市第一人民醫院病房大樓新建工程，砂土層噴錨網支護(撐)工法-------------------------------- 12
2.5.2 基地二：林口華亞科學園區研發大樓新建工程，紅土礫石層土釘加勁工法及斜坡明挖工法-------------------------------- 13
2.5.3 基地三：高雄市中華五路TESCO新建案，砂土層斜坡明挖工法----------------------------------------------------------------- 14
2.5.4 基地四：大台北華城加勁擋土牆背填砂土-------------------- 14
2.6 小結-------------------------------------------------------------------- 15
第三章 理論推導-------------------------------------------------------------- 16
3.1 有效應力分析邊坡垂直開挖-------------------------------------- 16
3.2 總應力分析邊坡垂直開挖----------------------------------------- 18
3.3 垂直邊坡土楔應力分析-------------------------------------------- 19
3.4 垂直邊坡破壞面之孔隙壓力分析-------------------------------- 22
3.5 垂直明挖之潛在破壞角θmax與時間之關係------------------ 24
3.6 邊坡自立高度分析-------------------------------------------------- 26
3.7 垂直開挖混凝土殼護坡穩定分析-------------------------------- 27
第四章 模型實驗-------------------------------------------------------------- 29
4.1 試驗材料及設備----------------------------------------------------- 29
4.2 模型製作-------------------------------------------------------------- 29
4.3 尺寸效應-------------------------------------------------------------- 30
4.4 試驗流程-------------------------------------------------------------- 32
4.5 模型試驗觀察及記錄----------------------------------------------- 32
4.6 模型試驗結果及討論----------------------------------------------- 33
第五章 工地驗證與分析----------------------------------------------------- 35
5.1 工地試驗規劃-------------------------------------------------------- 35
5.1.1 基地概況-------------------------------------------------------------- 36
5.1.2 地層分佈與土壤參數----------------------------------------------- 36
5.1.3 地下水位狀況-------------------------------------------------------- 36
5.1.4 現場負孔隙壓力分析----------------------------------------------- 36
5.2 工地開挖情形-------------------------------------------------------- 37
5.2.1 施工步驟及現況紀錄----------------------------------------------- 37
5.2.2 相關試驗-------------------------------------------------------------- 40
5.2.3 監測資料-------------------------------------------------------------- 40
5.3 斜坡明挖之應力分析----------------------------------------------- 41
5.3.1 毛細應力分析-------------------------------------------------------- 41
5.3.2 斜坡明挖含混凝土殼護坡之穩定分析-------------------------- 42
5.3.3 砂土地盤無腹地之土釘式護坡明挖技術----------------------- 61
5.3.4 土釘式護坡明挖技術之應力分析-------------------------------- 62
5.4 程式分析-------------------------------------------------------------- 65
5.4.1 STEDWin2.7程式分析--------------------------------------------- 65
5.4.2 RISS邊坡即時分析軟體------------------------------------------- 66
5.5 基樁影響評估-------------------------------------------------------- 67
5.6 角隅效應影響評估-------------------------------------------------- 67
5.7 安全性評估----------------------------------------------------------- 67
5.8 施工性評估----------------------------------------------------------- 68
5.9 經濟效益評估-------------------------------------------------------- 69
第六章 結論及建議----------------------------------------------------------- 70
6.1 結論-------------------------------------------------------------------- 70
6.2 建議-------------------------------------------------------------------- 71
參考文獻 -------------------------------------------------------------------------- 72
附錄一 -------------------------------------------------------------------------- 198
作者簡介 -------------------------------------------------------------------------- 214

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