液化地盤離岸風機單樁基礎之離心模型試驗

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题名:	液化地盤離岸風機單樁基礎之離心模型試驗
作者:	李政鋼;Li, Cheng-Kang
贡献者:	土木工程學系
关键词:	液化地盤;離岸風機;單樁基礎
日期:	2019-11-11
上传时间:	2020-01-07 14:21:29 (UTC+8)
出版者:	國立中央大學
摘要:	台灣近年環保意識崛起，因此風力發電可以替代火力或核能發電等非再生能源的方式逐漸被受到重視，更由於台灣西部沿岸風力資源豐富，進而發展離岸風機。然而台灣位於環太平洋地震帶，且西部沿岸海底多為疏鬆砂土，因此在地震發生時的淺層砂土發生液化可能性相當高。故本研究將以離心模型試驗探討單樁基礎(Mono-pile)土壤液化時的受震反應。本研究以德國離岸風力發電機組(Siemens SWT-4.0)之單樁基礎為原型，先將原型尺寸折減為35%，再依據尺度定律將折減後的單樁基礎進行80g的離心縮尺，模型樁底部採樁尖設計，樁底為自由端與試驗箱底部沒有接觸或連接。試驗配置以乾砂試體與飽和試體比較土壤液化發生時樁基礎的反應，並且討論不同的輸入震動波形(Sin-wave、Hamming-wave)對地盤與樁基礎的影響，因為Hamming-wave是非等振幅類正弦波，較接近真實地震波形，反之，Sin-wave容易高估現地發生地震時的受震行為，同時比較不同的液化土層厚度在發生液化時樁基礎的受震反應。從試驗結果顯示: (1)土層中的加速度振幅由基盤傳至地表逐漸放大，但發生液化後，由於剪力波無法傳遞，所以加速度傳至地表面時會大幅縮小，而飽和試體在未發生液化前，與乾砂試體有接近的加速度放大效應；(2)發生土壤液化時，土層承受最大彎矩深度增加，表示土層因液化導致強度下降，需要發展至更深層的土壤才有足夠束制樁的強度；(3)在相同的輸入震動下，Sin-wave時的樁基礎承受彎矩大於Hamming-wave時的反應，且相對於液化層厚度，Sin-wave甚至是控制液化程度的主因；(4)液化土層厚度增加，樁身受震時的撓曲彎矩有微小增加，同時土層承受最大彎矩深度持續向下發展，震後的殘餘旋轉角也有增加，輸入震動為Sin-wave的變化量相較於Hamming-wave更顯著。(5)液化程度愈高，上部結構慣性力影響樁基礎範圍愈深。 ;With a general awareness about environmental protection raises in Taiwan recent years, it has been attached that the way of wind energy are being substituted for non-renewable energy, like thermal power generation or nuclear power generation. Besides, offshore wind turbines has been developed on account of excellent wind resources in coastal areas of western Taiwan. However, Taiwan situates in Circum-Pacific Seismic Belt, therefore, the seabed in the western coastline of Taiwan is deposited with loose sandy soil that may be liquefied during earthquakes. The research results will give the reference to the mono-pile for offshore wind turbines. This study is based on the mono pile foundation of the German offshore wind turbine (Siemens SWT-4.0). This model uses two-stage scaling, the prototype size reduction to 35% of 1g model at first, and reduction to 80g scale model of centrifuge at second time. The pile tip is designed at the bottom of the model pile, and the bottom of the pile is free and not connected to the bottom of the test box. The test configuration compares the reaction of the pile foundation with the dry sand test and the saturated test when the soil liquefaction. At the same time, the effects of different input vibration waveforms (Sin-wave, Hamming-wave) on the ground and pile foundation are discussed, and compare the different liquefied soil thicknesses in the liquefaction of the pile foundation. According to the test results, the following conclusions can be drawn. (1) The acceleration in the soil layer is gradually amplified from the base plate to the surface, but it will decrease after liquefaction on the shear wave cannot be transmitted. (2) Produce the depth of soil layer with the maximum bending moment will increase after liquefaction. (3) When the pile foundation of the Sin-wave input motion is subjected to a bending moment greater than Hamming-wave at the same input amplitude. (4) The thickness of the liquefied soil layer increases, and the bending moment of the pile foundation is slightly increased during the earthquakes, generate the depth of soil layer with the maximum bending moment keep deepening, amount of change of the Sin-wave input motion is obvious to Hamming-wave. (5) The higher the degree of liquefaction, the deeper the inertial force of the superstructure to the pile foundation.
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