以離心模型試驗探討土壤再液化現象

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Title:	以離心模型試驗探討土壤再液化現象
Authors:	張晉豪;Chang, Chin-Hao
Contributors:	土木工程學系
Keywords:	離心模型試驗;土壤再液化;砂土層沉陷;土層中沉陷計;Centrifuge test;Soil reliquefaction;Settlement of the sandy soil;Layers settlement gauges
Date:	2024-01-24
Issue Date:	2024-09-19 14:45:39 (UTC+8)
Publisher:	國立中央大學
Abstract:	土壤液化為台灣常見的災害，位於台灣台南市新化區於西元1946年、2010年、2016年分別發生規模6.1、6.4、6.6的地震，當地地質多為粉土質砂土(SM)與砂質粉土(ML)，在同一處皆發生大規模液化，土壤反覆液化使得砂土層沉陷進而對建築物、管線等造成災害。本研究進行一系列動態離心模型試驗，使用積層版試驗箱對不同砂土條件進行分析，模擬土層厚度18m之砂土，飽和水位至地表，震動共有3種強度，強度由小至大施打，同一強度震動會連續施打5次以模擬現地連續受震情形，透過不同震波與強度對加速度、孔隙水壓、沉陷量進行討論。為進一步探討土層中的沉陷量，本研究透過線性可變差動變壓器(LVDT)之量測原理設計一套土層中沉陷計，此套設計主要包含沉陷板、外套管、滑輪組與釣魚線，透過拉線的方式以量測地表下指定位置的沉陷量，本研究於地表下6m與地表下12m放置土層中沉陷計欲將土壤平分為3層後續能夠對不同深度下的土壤進行分析與討論。試驗結果顯示: 砂土受震沉陷後其體積應變會趨於定值，之後所施打的震動砂土體積應變皆小於0.5%；從三層土層的沉陷量觀察到土層越淺沉陷量則會越大，土層越深其量測之沉陷量越小。兩試驗皆在第一次的震動事件(Sine Wave) 沉陷趨勢皆為整體 15 個震動事件中最大的，鬆砂在一定強度震動在第一次的震動後會有最大的沉陷量，到達一定的相對密度後其體積應變不會有太大的改變。發生再液化現象時，造成液化所需的震動週期數小於初始液化時所需的震動週期數，即土壤抗液化能力降低。 ;Soil liquefaction is a common disaster in Taiwan, particularly in the XinHua District of Tainan City. Earthquakes of magnitudes 6.1, 6.4, and 6.6 occurred in the years 1946, 2010, and 2016, respectively. The local geology primarily consists of silty sand (SM) and sandy silt (ML). Large-scale reliquefaction events occurred at the same location during each of these seismic events, causing the subsidence of sandy layers and resulting in disasters affecting buildings, pipelines, and other infrastructure. This study conducted a series of dynamic centrifuge model tests using a laminar shear box to analyze different sand conditions. The tests simulated saturated sandy soil with am 18-meters model ground, saturated water level up to the ground surface. Three levels of vibration intensity were applied sequentially, starting from the lowest and increasing in magnitude. For each intensity, vibrations were applied continuously five times to simulate the scenario of consecutive shaking. The study discussed the effects of different seismic waves and intensities on acceleration, pore water pressure, and settlement. To further investigate settlement in the soil layers, this study designed a settlement gauge based on the measurement principle of a Linear Variable Differential Transformer (LVDT), call layers settlement guage. This design comprises a settlement plate, casing, pulley assembly, and fishing line. The settlement gauge measures the settlement at specified locations beneath the ground surface by pulling system. In this study, settlement gauges were placed at depths of 6 meters and 12 meters below the ground surface to divide the soil into three layers. The sensor enables subsequent analysis and discussion of the soil at different depths. The test results indicate that the volume strain of the sandy soil tends to stabilize after seismic settlement, with subsequent vibrations inducing volume strains consistently below 0.5%. Observations of settlement in the three soil layers reveal that shallower layers experience greater settlement, while deeper layers exhibit smaller measured settlement. In both experiments, the settlement trend during the first vibration event S2-1(Sine Wave) is the highest among the 15 total vibration events. Loose sand experiences the maximum settlement after the initial vibration event at a certain intensity, and beyond a certain relative density, its volume strain does not undergo significant changes. In the occurrence of reliquefaction, the number of vibration cycles required for reliquefaction is less than that needed during the initial liquefaction. This implies a reduction in the soil′s anti-liquefaction capacity.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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