A Study on the Reasons for No Soil Liquefaction Occurring in the Lanyang Plain in a Strong Earthquake Area

The Lanyang Plain is prone to earthquakes of magnitude 5 or higher. The Central Geological Survey’s soil liquefaction potential map of Yilan County shows that more than 69% of the plain area has high liquefaction potential: but why have there not been any liquefaction cases in the past 23 years? Based on the results of the groundwater pumping test, geological history, and the soil liquefaction analysis method, this study aimed to explore and analyze the causes of no liquefaction occurring in the Yilan region. To understand the permeability of the overall stratum structure of the Lanyang Plain and the spring phenomenon, the relationship between groundwater well-pumping test results and the permeability coefficient experience formulas was first studied. Then the Chapuis’ experience formula of the K value multiplied by 10 was recommended herein such that the permeability coefficient K values of the Lanyang plain could be estimated with large numbers. The reasons for the absence of liquefaction cases in Lanyang plain were then investigated. It was found that less serious earthquakes occurred and combined with the extremely ideal permeable soil conditions existing in the Lanyang plain, this led to no catastrophic liquefaction cases occurring over the last 23 years.