以離心模型模擬不同粒徑分佈砂層於液化時之行為;centrifuge modeling on behaviors of liquefied sandy soils with different particle size distribution

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题名:	以離心模型模擬不同粒徑分佈砂層於液化時之行為;centrifuge modeling on behaviors of liquefied sandy soils with different particle size distribution
作者:	梁友承;Liang, You-Cheng
贡献者:	土木工程學系
关键词:	離心機;土壤液化;centrifuge;soil liquefaction
日期:	2019-08-26
上传时间:	2019-09-03 12:16:49 (UTC+8)
出版者:	國立中央大學
摘要:	在過去的歷史事件中，世界各地因強震所引致之土壤液化而造成人民的生命及財產受到威脅，例如大面積的地表沉陷，建築物傾倒、邊坡滑移及測潰等。土壤液化易發生在飽和的砂質地盤，尤其在地震帶上更為高度土壤液化淺勢區，以日本為例，在1964年日本新瀉大地震而伴隨著大規模的土壤液化，使許多上部結構物發生傾倒的災害，進而促使各國學者更為重視在土壤液化引致的相關議題上。本計畫藉由中央大學地工離心機暨振動台進行土壤液化與側向滑移之試驗。在離心模型中埋置多種感測器，如垂直地中位移計觀察土壤位移情況、縮尺圓錐貫入試驗比較液化前後之土壤沿深度阻抗、加速度計、孔隙水壓計與位移計等觀測土壤在26倍的人造重力場中受震時之反應。本研究探討以 5 度緩坡在不同粒徑之土壤，比較在相同相對密度但不同孔隙比及相同孔隙比但不同相對密度，並與LEAP2017年之試驗結果相互比對驗證在受震期間液化行為的差異性。試驗結果顯示：(1)在一樣的高度液化區域範圍內，相同的孔隙比及不同的相對密度，皆對液化深度有間接的差異性；(2)在相同相對密度下，孔隙比較大的土壤會較易達到液化；在相同的孔隙比下，相對密度較疏鬆的也會較快達到液化；(3)表層土壤因初始有效應力較小，較容易達到土壤液化行為，而試體因斜坡的關係，土層厚度及孔隙比大小也會影響超額孔隙水壓的消散速率；(2)土層因液化發生側潰，地表位移方向均向斜坡下方處位移，其位移量也隨液化深度成正比，但因受柯氏力的影響，在走向的位移會偏離震動方向；(3)液化後因發生側潰使土層產生側向位移，其側潰量與液化深度成正比，隨深度愈深而減小，在地表下一定的深度後就停止側向移動；(4)錐尖阻抗延著貫入深度增加而增加，受震後阻抗變化量也隨之增加，而錐尖阻抗較小的土樣也會有較深的液化深度。 ;In the past, people′s lives and property have been threatened by soil liquefaction caused by siginificant earthquakes around the world. Such as large area ground surface settlement, toppling of buildings, slope displacement. Soil liquefaction is easily happened in saturated sand layer, especially in the region of erathquake. For example, niigata earthquake happened in 1964 in Japan and accompanied by large area soil liquefaction. Make a lot of upper structure of dumping disasters occur, which leads to be more of international scholars in the soil liquefaction caused by related issues. This project was conduct experiments of soil liquefaction and lateral spreading by National Central University geotechnical centrifuge and shaking table. A variety of sensors were embedded in the centrifuge model, such as vertical displacement transducers to observe soil displacement, reduce scale cone penetration test to compare resistance before and after liquefaction, accelerometers, pore water pressure transducers and markers to observe soil response under 26 times of artificial gravity field. This study will compare to different pore ratios of the same relative density and the same pore ratio but different particle sizes on a 5 degree slope. The results of LEAP2017 test to verify the difference of liquefaction behavior during earthquakes. The test results show that : (1) In the same high liquefaction region, the same pore ratio and different relative densities have indirect differences in liquefaction depth. (2) Under the same relative density, soil with large pores will be easier to liquefy; under the same pore ratio, the looser relative density will reach liquefaction quickly. (3) the initial effective stress of surface soil is small, so it is easy to achieve soil liquefaction behavior. However, due to the relationship of slope, the thickness of soil layer and the size of pore ratio also affect the dissipation rate of excess pore water pressure. (2) As the soil layer collapses due to liquefaction, the displacement direction of the surface were all shifted to the lower part of the slope. The displacement was proportional to the liquefaction depth. However, due to the influence of the coriolis force, the displacement in the strike direction will deviate from the direction of vibration. (3) After liquefaction, lateral displacement of soil layer occurs due to lateral collapse. The amount of lateral collapse is proportional to the liquefaction depth, and decreases with the deeper the depth. Lateral movement stopped after a certain depth under the surface. (4) The impedance of the cone tip increases with the increase of penetration depth, and the variation of the impedance after the earthquake also increases.
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