Underground construction in decomposed residual soils

Large scale underground construction projects, including subway construction projects in six major cities, have been ongoing in Korea, where residual and granite soils are the most common soil type. Characteristics of decomposed granite soils are different from those of pure sand and/or clay. This paper presents an overview of geotechnical aspects of underground construction in urban areas where mostly decomposed residual soils are present, focusing on mechanical properties, apparent earth pressure, effect of groundwater, and effect of spatial variability in geotechnical properties. Although several important aspects are theoretically, numerically, and experimentally discussed herein, it remains a challenge to fully understand residual soils, particularly in relation to the practice of underground construction, because of their complexity and richness.