Abstract

Volcanic activity often creates very complicated volcanic complexes due to interlayering of lava flows and volcanic ash. Song-Gok site, composed of volcanic rocks, collapsed at the lower part of the slope along several discontinuities around a fault. The result of kinematic analysis indicated the possibility of plane, wedge, and toppling failure in the failure section. The result of Distinct Element Method(DEM) showed that maximum displacement is 207mm and joint shear displacement is 114mm. A yield zone was verified at the fault plane of the failure section. Volcanic rock slopes have unfavorable geotechnical characteristics, which is caused by differential weathering, effect of groundwater based on permeability of rocks, and systematic joints generated by cooling and contraction of lava. When considering the stability of volcanic rock slopes, data such as geological features of the rock through detailed geological survey and variations of discontinuities and rock blocks should be utilized.

1. INTRODUCTION

Most of Korea consists of mountainous topography, and thus artificial slopes have continuously been produced during the construction of infrastructures such as roads and railways. In particular, sections with a high road usage have recently increased due to the interest in new tourist attractions and changes to administrative and residential centers. Accordingly, construction on existing roads is in progress throughout the country. To secure the stability of slopes produced during construction work in advance, MLTM (2011) provides guidance through literature survey, topographic interpretation, geophysical exploration, geological ground survey, and various tests so that more stable slopes can be formed. However, for the new excavation or re-excavation of slopes, collapse frequently occurs during the excavation work. Even though the characteristics of rocks and the direction of major discontinuities are examined through geophysical exploration or boring investigation in the initial design process, slopes that are exposed during or after actual excavation could show unexpected unstable geologic structures, or partial weak zones could be formed due to the effects of the change in the weathering condition and the difference in the groundwater conditions and seepage over time. Therefore, for these slopes, the stability needs to be re-evaluated after examining the characteristics of weak zones in each section by performing a resurvey during construction and by making a detailed face map so that more stable slopes can be formed.

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