振動台大型試體受震體積應變之探討

Volumetric Strain of Large Specimen in Shaking Table Test

吳繼偉(Ji-Wei Wu)

指導教授 ： 翁作新

國立臺灣大學/工學院/土木工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00465

摘要

摘要

飽和砂土在受到地震或振動作用時會激發超額孔隙水壓，振動結束後超額孔隙水壓逐漸的消散，隨著超額孔隙水壓的消散，砂土層的體積會減小，使得砂土表面產生沉陷。1999年集集地震使台灣中部許多砂性土層地區發生液化，例如台中港區、員林、霧峰及南投等地區，顯示出砂性土壤液化問題在台灣地區有進一步研究之必要性。本文利用國家地震工程研究中心之大型剪力盒及振動台進行大尺寸物理模型振動試驗，此試驗盒採用多層框架堆疊而成，試驗盒內框裝容試體尺寸為1.880 m × 1.880 m × 1.520 m。每層內外框設置線性滑軌而相互獨立運動，使土壤試體能如現地水平土層隨地震波作用而變形，模擬實際地震剪力波在水平土層中傳遞的情形。
翁作新等人自2002年八月起以飽和越南砂試體進行一系列振動台振動試驗，到目前為止已進行八次振動台試驗。由本研究整理歷次試驗的結果顯示飽和砂土層受振若未發生液化則砂土層整體平均體積應變與振動加速度、振動頻率、振動延時及振動方向無明顯關係。飽和砂土受振液化後，在相同的振動延時下，體積應變只與相對密度有關而與振動加速度、振動頻率及振動方向無關，且隨著相對密度的增加而減少；液化後砂土之體積應變隨著振動延時的增加而增加，利用不同振動延時（5、10、20及30秒）可繪出四條趨勢線，利用此關係配合現地之土層資料即可推估該地受震液化後會產生之沉陷量。比較實際地震歷時記錄所進行之振動台試驗及現地量測資料之體積應變可得知本研究結果有不錯之適用性。

關鍵字：液化、大型剪力盒、振動台、體積應變、沉陷、地震、砂

關鍵字

液化、大型剪力盒 ； 振動台 ； 體積應變 ； 沉陷 ； 地震 ； 砂

並列摘要

Volumetric Strain of Large Specimen in Shaking Table Test
ABSTRACT

The shaking due to earthquakes or vibrations will generate excess pore water pressure in saturated sand. After shaking, the excess pore water pressure in the saturated sand layer dissipates with time, and the volume of the sand layer decreases and settlement occurs. In 1999, Chi-Chi Earthquake caused liquefaction in many areas with sandy soil layer in mid-Taiwan, for example, Taichung Seaport, Yuanlin, Wufeng and Nantou area. This experience alarms us that there is necessity to study further the liquefaction problem of sandy soil in Taiwan. In this study, a biaxial laminar shear box on a shaking table at National Central Research of Earthquake Engineering (NCREE) was used to conduct the shaking tests of a large-scale physics model. The dimension of the specimen is 1.88 m × 1.88 m × 1.52 m. The shear box is composed of 15 layers of inner and outer frames. For each layer, the frame motion (inner frame and outer frame) is independent from other layers. The soil sample deformed according to the shear waves induced from the shaking table motions.

Ueng et al.（2002）used the saturated sand from Vietnam. So far, eight series of shaking table tests has been performed. The test results showed that if liquefaction did not occur, there is no obvious relation between the average volumetric strain of the sand and the acceleration of vibration, frequency of vibration, duration of vibration, or mode of vibration. When liquefaction occurred, for the same duration of vibration, volumetric strain is only related to relative density, but not acceleration of vibration, frequency of vibration or direction of vibration. Volumetric strain decreases with increase of relative density, and increases with increasing shaking duration. These relations can help us to calculate the quantity of settlement due to liquefaction. This research has been verified by the shaking tests with the recorded earthquake motions and the field settlement data.

Key words: liquefaction,laminar box,shaking table,settlement,volumetric
strain,sand,earthquake.

並列關鍵字

liquefaction ； laminar box ； shaking table ； settlement

參考文獻

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