Damage investigation and liquefaction potential analysis of gravelly soil

With frequent shocks in Taiwan, located on the Pacific earthquake belt, it is found that injury and structural destruction are often induced by soil liquefaction. From past experience, it is known that soil liquefaction generally occurs in saturated sand or silty fine sand. However, in the areas of Wufeng, Nantou and Armenia where gravelly soils were liquefied, further studies need be conducted on the liquefaction potential of this soil. The Fu Tin Bridge site in Wufeng, where liquefaction occurred during the Chi‐Chi Earthquake, was selected for the liquefaction study in a gravelly deposit. Extensive in situ index tests, including field density, grain size distribution, and water content were conducted in the testing trench. Furthermore, a series of remolded large scale cyclic triaxial tests (15 cm in diameter, 30 cm in height) using the same gravelly soil were performed to study the variation of liquefaction resistance, due to relative density and gravel content. Another series of tests for pure sand in different relative densities were performed to compare the effect of gravel content. The test results show that an increase in the gravel content or the relative density increases its liquefaction resistance, and decreases the axial strain. In addition, the liquefaction resistance of soil with gravel content in the range of 20% to 40% with relative density of 40% shows the same strength as those of pure sand with relative density between 50% and 70%. Finally, a regression equation between the variation of parameters (gravel content and relative density) and the liquefaction resistance can be obtained for gravelly liquefaction assessment.