英文篇名
Geosynthetic-Reinforced Slope Model Test ~ Comparisons of Dynamic and Pseudo-Static Behavior
作者
黃景川
關鍵字
地工合成物加勁邊坡、模型試驗、傾斜試驗、震動台試驗
摘要
本研究以高度為480 mm,坡角為60之地工合成物加勁邊坡(Geosynthetic-reinforced slope)模型進行擬靜態之傾斜試驗(Tilting test)及震動台試驗(Shaking table test),探討動態加載時輸入波頻率及振幅大小對坡頂加速度增幅(Amplification)之影響。本研究同時探討加勁邊坡在擬靜態慣性力及動態之地震力作用下,其位移反應之相關性。本研究發現,加勁邊坡在正弦波之動態力作用下,坡頂之水平加速度增幅狀況隨著邊坡內部滑動面之有無(或邊坡之最大水平變位Dmax與坡高Ht之比值)而有顯著的不同。坡頂之加速度振幅比(Amplitude ratio, Am)隨輸入尖峰地表加速度HPGA值(或Dmax/Ht值)之增大而減小。從邊坡內部滑動面之發展過程可以發現,Am值隨著邊坡內部主要滑動面之發生,從Am > 1之加速度增幅反應逐漸轉變為Am < 1之加速度減幅狀態。因此,地工合成物加勁邊坡之耐震設計中,由於邊坡設計考量變位程度之不同,所需考慮的坡頂加速度增幅狀態亦有所不同。根據不同加載頻率(f = 3Hz, 6Hz, 15Hz)之Am vs. HPGA曲線,將Am = 1.0之HPGA值定義為邊坡從彈性(或完整)狀態進入塑性(或分割)狀態之臨界點,可發現臨界HPGA值隨正弦波頻率之減小(或週期之增大)而減小。當f = 3Hz時,臨界HPGA值約略等於擬靜態載重下之降伏慣性力khcg。此一結果初步証實Huang et al. (2008)之假說,認為擬靜態試驗中之側向慣性力施加方式近似於以週期相當大之動態加載所施加之慣性力。
英文摘要
Four identical geosynthetic-reinforced slopes with a height of Ht = 480 mm, and a slope angle of = 60 were established and loaded to ultimate failure conditions via tilting box and shaking table test facilities. These reinforced slopes simulate idealized 2-D, round particle backfill, by using 150 mm-long, 1.96 mm-diameter stainless steel rods. Extensible non-woven geotextile reinforcement was used in conjunction with a 2 mm-thick aluminum facing plate which simulates a 51 mm-thick concrete facing for a 2 m-high reinforced soil slope. Shaking table tests were conducted under a uni-axial shaking condition, using sinusoidal single-cycle waves with frequencies of f = 3Hz, 6Hz, and 15Hz. For each series of tests with a specific wave frequency, input horizontal peak ground accelerations (HPGA) were step-wise intensified until the ultimate displacement state of the slope. It was found that the acceleration amplitude ratio (Am) at the crest of the slope is a function of HPGA (or Dmax/Ht), and wave frequency (f). They generally increase with the increase of f, while they decrease with the increase of HPGA (or Dmax/Ht). It was also found that a transition from an amplification state (Am > 1) into a de-amplification state (Am < 1) occurs when major sliding planes were extensively mobilized within the backfill. Test results generally support a hypothesis made earlier that the pseudo-static tilting load is a special case of dynamic seismic load with a significantly large period (or small frequency).