減振基樁之瞬間變形與減振效果; Model pile tests on the mitigating effects of vibration and immediate deformation

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题名:	減振基樁之瞬間變形與減振效果;Model pile tests on the mitigating effects of vibration and immediate deformation
作者:	林筠原;Yun-yuan Lin
贡献者:	土木工程研究所
关键词:	振波衰減;減振彈簧;動態位移量;減振基樁;attenuation of wave propagation;shock-absorbing spring;dynamic displacement;pile of vibration suppression
日期:	2009-06-24
上传时间:	2009-09-18 17:26:33 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	當交通運輸工具通過高架橋或橋樑路段時，對橋墩產生一衝擊能量，該衝擊能量首先傳遞至基樁，而基樁受一衝擊能量後，能量迅速由樁身傳遞至樁尖，於承載層形成一震源，向四周擴散傳播，之後經由各種折射、反射等現象將會造成土層或地表振動。另外，基樁振動除了樁尖所產生之壓力波外，樁身週遭土壤的相對運動或樁身周圍的土壤本身之相對變形均會產生剪力波，向外傳遞而出，因此希望直接透過橋墩下之基樁本身之改良設計來達到減振效果。本研究利用液壓之方式與彈簧組合成一液壓彈簧複合式減振器，並進行一系列的模型試驗，彈簧可調節減振效果；液壓可控制最大動態變位量，組合其兩種不同之物理機制，可使基樁之最大動態變位量符合規範，且可達到最佳之減振效果。依照減振器內部配置不同，可將減振器分為六個型式，藉由模型試驗探討不同型式減振器加裝於基樁上時，對於樁尖在承載層中產生振波之減振效果、原型樁與改良樁之樁周土壤中振波波傳衰減行為、衝擊加速度與減振器最大動態變位量之關係。實驗結果可知，樁身所承受之衝擊能量係藉由樁身傳遞至樁尖，再以樁尖為主要振源，向四周土壤傳遞能量。純彈簧之減振器減振效果最佳，但其最大動態變位量已高達5.14mm，而減振器填充水量之後可將最大動態變位量抑制於0.5mm以下，且其減振效果亦可高達50％，表示液壓彈簧減振器不僅達到了減低衝擊荷重產生之振波傳至樁尖之成效，亦能有效地將動態變位量降低。 It will generate impact energy to piers while transportation vehicles pass a viaduct or a bridge. This impact energy will be transmitted to pile foundation and then to the pile tip. A new vibration source will be formed in the bearing stratum and spread out. The vibration in soil layers or ground surface will be refracted and reflected. Besides, the vibration will transmit two kinds of waves. One is P-WAVE that is from pile tip, and the other one is S-WAVE that is caused by the relative movement in soil around pile shaft or the relative deformation in soil. Therefore, it is important to design a new pile shaft to decrease this impact energy. This research performed a series of model pile tests by using a composite device of hydraulic cylinder and shock-absorbing spring. The spring can be used to adjust the effect of vibration mitigation and the hydraulic cylinder can be used to control the dynamic displacement. This dynamic displacement of pile foundation can be controlled to fit standard of the design code and may obtain the best effect of vibration mitigation by combining these two different physical systems. According to the different parts inside the shock absorbing devices, it can be divided into six kinds of types. With different types of shock absorbing devices, the relationships among the effect of vibration mitigation in bearing stratum, the behaviors of attenuation of wave propagation around treated and untreated piles in soil layer, the impact acceleration and the dynamic displacement were studied. According to the results of experiments, it can be found that the impact energy is transmitted from pile shaft to the tip, and then to the surrounding soil. The best effect of vibration mitigation will be obtained by using pure spring. However, its dynamic displacement reached 5.14mm. If the shock absorbing device is fully filled with water, the settlement can be reduced to less than 0.5mm. And the best effect will reach 50%. It means that the composite device of hydraulic cylinder and shock-absorbing spring not only can reduce the impact energy but also can decrease the dynamic displacement efficiently.
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