位於可液化砂土層中單樁基礎受震反應的離心模擬

Centrifuge modeling on the Seismic Response of Mono-pile Foundations in Liquefiable Sandy Soil Subjected to Earthquake Loading

凃亦峻(Yi-chun Tu)

指導教授 ： 李崇正

國立中央大學/工學院/土木工程學系/碩士(2011年)

摘要

台灣雖然擁有豐富的風資源，但東海岸地形陡峭，並不適合發展離岸風力發電，因此風力發電設施多設置於西部沿海。然而西岸海底表層多屬於疏鬆砂土，地震時淺層砂土發生液化的可能性相當高，而國外目前對位於地震區的離岸風力電廠，其風力發電機組之基礎土壤發生液化對基礎穩定的評估方法尚無深入研究。本研究以離心模型試驗探討單樁基礎土壤液化時，單樁基礎的受震反應。
本研究以丹麥離岸風力發電機組(Horns Rev 1)之單樁基礎為原型，先將原型尺寸折減為40%，再依據尺度定律將折減後的單樁基礎縮尺，設計製作八十分之一的單樁基礎模型，在80g的離心加速度場進行試驗。離心模型試驗過程分別量測樁身彎矩歷時、加速度歷時、樁頂位移歷時與地表沉陷，並利用回歸分析求取單樁樁身彎矩分佈隨時間的變化。
試驗結果顯示，基樁受震時，乾砂試體最大彎矩量發生在深度4m(z/L=0.21)處，飽和砂試體最大彎矩量發生在深度6.4m(z/L=0.33)處，顯示淺層土壤液化時，土層束制基樁的深度會向深層發展。而當基樁上部載重塊的高度越高，由於基樁受震時上部載重產生的傾覆彎矩較大，因此樁身產生的彎矩量以及樁頭位移量較大。此外利用p-yΔ曲線法計算地盤反力係數kh，其結果顯示飽和砂試體淺層土層在超額孔隙水壓比ru值最大時kh接近最小值，深層土壤整體而言kh隨著振動週期數的增加而增加。

關鍵字

單樁基礎 ； p-yΔ曲線法 ； 超額孔隙水壓比 ； 地盤反力係數 ； 液化 ； 模型計測樁

並列摘要

Offshore wind farms have recently been developed very maturely in Northern European country. Although the wind energy resource in the western coastline of Taiwan is very abundant, the offshore wind power industry has not been developed. Taiwan is located in the seismic zone, and the sea bed in the western coastline of Taiwan is deposited with very loose sandy soil that may be liquefied during large earthquakes. The current design code of wind turbine foundation does not give the detailed requirements of earthquake resistant design. And thus, a design guideline or code which proved by centrifuge modeling tests is strongly needed before construction projects undertaking. The research results will give the reference to the mono-pile for offshore wind turbines.
In this study, a series of dynamic shaking table tests of mono-pile foundations was conducted for the centrifuge pile models embedded in liquefiable sandy soil and carried out at an 80-g acceleration. According to the test results the fallowing findings were obtained. The maximum bending moment of pile in dry sand occurred at the depth of 4m (z/L=0.21) and the maximum bending moment of pile in saturated liquefiable sand occurred at the depth of 6.4m (z/L=0.33). The induced bending moment and the pile displacement are higher when the tip mass fixed on the top of the mono-pile foundations. The coefficient of horizontal subgrade reaction can be calculated by p-yΔ curve method. The values of the coefficient of horizontal subgrade reaction in shallow depths decrease while the excess pore water pressure increase during shaking. In the case of deep soil, the values of coefficient of horizontal subgrade reaction increase with the increasing number of cycles of shaking. And the coefficient of horizontal subgrade reaction suggested by Reese consist with the experimental results.

並列關鍵字

excess pore water pressure ； p-yΔ curve method ； coefficient of horizontal subgrade reaction ； mono-pile foundation

參考文獻

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