Model Tests to Determine Bearing Capacity of Spudcans Penetrating Submerged Loose Sand
|關鍵字:||承載力;模型試驗;相對密度;支撐基腳;自升式安裝船;Bearing capacity;Model test;Relative density;Spudcan;urbine installation vessel|
|摘要:||本研究以室內實驗方法探討不同尺寸支撐基腳貫入浸水疏鬆砂土之極限承載力。本研究使用渥太華砂為實驗試體，進行1g spudcan模型試驗實驗。本研究在交通大學基礎模型試驗室自行設計及建造之spudcan模型試驗系統包含：垂直加載系統、試驗土槽及支撐基腳。為模擬台灣彰化西部沿海之疏鬆砂土，本研究使用砂斗提升法備製均勻土壤試體，並以砂斗開口大小(7 mm)及砂土落距(200 mm)控制砂土試體之相對密度為15%。本研究將渥太華砂試體於試驗土槽浸水，並以suction pump抽除土壤孔隙之空氣，以模擬海床浸水土壤行為。當spudcan貫入浸水砂土之貫入量 S 等於貫入之spudcan直徑(1D)時，測得之沉陷剖面大致左右對稱，沉陷影響區延伸至spudcan外側的D/2。D = 150 mm圓形spudcan貫入浸水砂土之實驗結果顯示，在spudcan貫入量S = 0 至300 mm過程，模型試驗測得之極限垂直承載力qu與採用SNAME手冊理論計算之極限承載力符合良好。實驗結果顯示，極限支承力qu隨著spudcan直徑增加(D = 150、200、300 mm)而逐漸增加。此實驗結果之趨勢，與以SNAME設計手冊理論公式計算不同直徑spudcan造成之極限承載力qu大小趨勢一致。不論spudcan直徑大小，模型試驗求得之極限承載力皆等於或大於SNAME手冊求得之理論值，顯示SNAME手冊之設計值為保守，是在安全的一側。|
This thesis investigated the bearing capacity of spudcans with different diameter(D = 150、200 and 300 mm) penetrating submerged loose sand. Ottawa sand was used to conduct the 1g model tests at National Chiao Tung University. The spudcan experiment system consists of the vertical loading system, soil bin, and model spudcans. To simulate the offshore loose soil behavior in west Taiwan, the air-pluviation method was used to control relative density of Ottawa sand. With the slot opening 7 mm and a drop distance of soil particles 200 mm the relative density of 15 % was achieved. Allow water inflow to inundate soil specimen then use the suction pump to remove air in the soil void. The relative density of the loose submerged sand was 26 %. When spudcan penetrate the submerged soil to the depth equal to the spudcan's diameter, it was found that the surface settlement trough was symmetrical, and the trough extended to D/2 from the edge of spudcan. For the penetration of the diameter 150 mm spudcan into the submerged sand, experiment of bearing capacity was in good agreement with the bearing capacity calculated with the SNAME. For all tests of spudcan penetrating submerged sand, it was found the experimental bearing capacity increased with increasing spudcan diameter. All experimental results were equal to or bigger than the bearing capacity calculated following the SNAME. The ultimate bearing capacity estimated with SNAME was on the safe side.
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