振動台大型剪力盒試驗砂土液化後沈陷量之研究

程漢瑋(Han-Wei Cheng)

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(2004年)

https://doi.org/10.6342/NTU.2004.01267

摘要

飽和砂土在地震中或地震後，土層內激發的超額孔隙水壓隨著時間消散而使飽和砂土層的體積減小，引致砂土層表面產生沈陷。本文利用國家地震工程研究中心之大型剪力盒在其振動台上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 x 1.880 m x 1.520 m。每層內外框與他層內外框設置線性滑軌而相互垂直獨立運動，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。
本文以飽和越南砂試體進行一系列振動台振動試驗，到目前為止已進行五次振動台試驗。振動台輸入振動模式為：加速度0.03 g至0.15 g，振動波型為均勻正弦波，其振動頻率為1 Hz、2 Hz與4 Hz，分別進行一維與二維之振動試驗，其振動延時為5秒、10秒及20秒。由試驗結果顯示飽和砂土受振動時不論有無發生液化現象皆有沈陷量之產生，且沈陷量皆隨振動延時增加亦有增加之趨勢。未發生液化之砂土層相對於液化土層所產生的沈陷量小很多。當飽和砂土受振時，振動加速度振幅增加則液化時產生之沈陷量愈大；而相同加速度振幅時，二維振動砂土液化時之沈陷量較一維振動砂土液化時之沈陷量大。由沈陷量計算液化土層之體積應變，發現液化土層液化後之體積應變與其相對密度有一定之關係，而不受加速度大小與單向或水平多向振動之影響。本研究之振動台試驗中液化土層之最大剪應變介於 0.5% ~ 3.5%間，所得液化土層液化後之體積應變與前人研究結果相近。

關鍵字

振動台 ； 液化 ； 沈陷量

並列摘要

During or after earthquake, the seismically induced excess pore water pressure in saturated sand layer would dissipate with time, and the volume of the sand layer decreases and settlement occurs. 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 large-scale physics model. The dimension of the specimen is 1.88 m x 1.88 m x 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.

In this study we used the saturated sand from Vietnam. So far, five series of shaking table tests has been performed. The input motions for the shaking table are uniform sinusoidal wave shaking with acceleration amplitudes from 0.03 g to 0.15 g, frequence of 1 Hz, 2 Hz, and 4 Hz and duration of 5 sec, 10 sec, and 20 sec. One dimensional and two dimensional shaking tests were carried out. The results from these tests showed there are settlements in the saturated sand, being liquefied or not, and the settlement tends to increase with shaking duration. Beside, the settlement in non-liquefied sand layer is much smaller than that in liquefied one. The settlement during liquefaction increases with the acceleration amplitude. For the same acceleration amplitude, the settlement in 2D shaking is larger than that in 1D shaking. It is observed that the volumetric strain of the liquefied sand layer relates to its relative density, but not to either the acceleration or the direction of vibration (1D or 2D shaking). In this study the maximum shear strain in the liquefied sand layer is between 0.5% and 3.5%, and the volumetric strain after liquefaction of the sand layer is similar to prior researches by others.

並列關鍵字

shaking table ； liquefaction ； settletment

參考文獻

【1】Kramer, S.L. ”Geotechnical Earthquake Engineering ,” Prentice-Hall International Series in Civil Engineering and Engineering Mechanics, Upper Saddle River Hall NJ07458 (1996)

【7】Tokimatsu, K. , and Seed, H.B., “Evaluation of Settlements in Sands Due to Earthquake Shaking,” Journal of Geotechnical Engineering, Vol. 113, No. 8, pp. 861-878 (1987)

【8】Nagase, H and Ishihara, K., “Liquefaction-Induced Compaction and Settlement of Sand During Earthquakes, “ Soils and Foundations, Vol. 28, No. 1, pp. 65-76 (1988)

【9】Ishihara, K. and Yoshimine, M., “Evaluation of Settlements in Sand Deposits Following Liquefaction During Earthquakes,” Soils and Foundations, Vol. 32, No. 1, pp. 173-188 (1992)

【11】Yoshimi, Y., Kuwabara, F. and Tokimatsu, K. “One-Dimensional Volume Change Characteristics of Sands Under Very Low Confining Stresses,” Soils And Foundations, Vol. 15, No.3, pp. 51-60 (1975)