Model Tests to Estimate Bearing Capacity of a Spudcan under Jack-up Turbine Installation Vessel
|關鍵字:||支撐基腳;破壞機制;模型試驗;貫穿;水中霣降法;自升式安裝船;spudcan;failure mechanism;model test;punch through;water- pluviation method;turbine installation vessel|
|摘要:||本研究以實驗方法探討自升式風機安裝船支撐基腳(spudcan)承受垂直荷重，在飽和疏鬆砂土造成之破壞機制。交通大學支撐基腳模型試驗設備包含以下5個部分：(1)反力架；(2)試驗土槽；(3)支撐基腳；(4)垂直荷重加載系統；及(5)資料擷取系統。台灣電力公司對彰化離岸風力發電區進行地質鑽探及現場試驗，得到彰化離岸風力計畫區海床表面至12 m深度砂土之SPT-N值大約介於7 ~ 21之間，其相對密度介於Dr = 15 ~ 46%。本研究採用水中霣降法在水中製作均勻砂土試體，並以篩網開口大小、及砂土沉降落距控制試驗土樣之相對密度，模擬台灣西部沿海沖積土壤於海水中緩慢沉澱形成之土層。實驗結果顯示，以水中霣降法備製砂土試體，不論砂土顆粒通過10號或20號篩網，砂土試體之相對密度，皆隨砂土在水中沉降落距之增加而加大。若欲形成相對密度為15 ~ 46%之試體，可以優先使用200 mm之沉降落距與10號篩網。Vesic (1973)說明當土壤相對密度小於35%，土壤受到荷重加載發生punching shear failure，此種情況下土壤的破壞面不會延伸到地表面，比較實驗結果，以水中沉降法備製之砂土試體，平均相對密度為23.2%，spudcan貫入土層100 mm時，spudcan下方砂土產生位移，但破壞面並無發展到表面，符合Vesic(1973) punching shear failure。根據Vesic (1963)相對密度與載重關係圖，依據圖中之關係可以得到極限承載力為qu= 71.6kN/m2，Qu = 2.53 kN。當極限承載力Qu為2.53 kN時，所對應之沉陷量為30 + 42 =72 mm，與實驗結果相比，當沉陷量為100 mm時，所對應之荷重為2.57 kN與依Vesic(1963)求出之極限承載力Qu = 2.53 kN相近。|
In this thesis investigated the mechanism of failure from the bearing capacity of a spudcan under Jack-up turbine installation vessel in saturated loose sand. The spudcan experiment system at the National Chiao Tung University consists of the following parts: (1) reaction frame; (2) soil bin; (3) model spudcan; (4) vertical loading system; and (5) data acquisition. According to the results of the situ tests and the geo-drillings at Changhua offshore wind power distinct from Taiwan Power Company. Knowing the SPT-N of sand from seabed to depth 12 m is between 7 and 21 in Changhua offshore wind power project distinct, and the relative density of the sand is between 15 to 46%. To achieve a uniform soil specimen, the water-pluviation method was adopted. The relative density of Ottawa sand was controlled by the sieve opening and the drop distance between the sieve and the density cup. Preliminary test results indicated that, whether using sieve No. 10 or No. 20, the relative density of the specimen increases with increasing drop distance of soil particles in water. To achieve the relative density (15 to 46%) of the seabed soil density on the west coast of Taiwan, the drop distance of 200 mm and the sieve No. 10 are recommended. Vesic (1973) said that the soil got overload and the soil would happen punching shear failure when the relative density was below 35%. The failure surface would not to extend ground surface. In test, make the sand specimens by water-pluviation method, we got the average relative density was 23.2%. Penetrating spudcan to the sand layer to depth 100 mm, the sand under the spudcan would have displacement but the failure surface would not to extend to groud surface. The test result coincided the research of Vesic (1973). According to the figure of relative-load of Vesic(1963). Getting ultimate capacity was qu=71.6 kN/m2, Qu=2.53 kN. When the ultimate capacity was 2.53 kN that the corresponding settlement was 30+42 =72 mm. Comparing the test results and Vesic’s researching, when the settlement approach to 100 mm, the corresponding loading was 2.57 kN which was near to ultimate capacity Qu=2.53 kN from Vesic (1963).
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