| dc.description.abstract | 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. | en_US |