Sand Liquefaction Observed During Recent Earthquake and Basic Laboratory Studies on Aging Effect

Abstract

During the 2011 Tohoku Pacific Ocean earthquake (M9.0), liquefaction occurred extensively in reclaimed land in Kanto area more than 200km far from the earthquake fault. The liquefied sand generally contained a lot of non-plastic fines with fines content more than 50% in some places. Almost all sand deposits along the Tokyo bay area reclaimed in 1960s or later liquefied, while in a good contrast, those older than that did not. In order to study the aging effect on liquefaction strength of sands containing fines, a series of basic laboratory tests combining innovative miniature cone penetration and subsequent cyclic undrained loading were carried out in a modified triaxial apparatus on sand specimens containing fines. A unique curve relating cone resistance qtand liquefaction strength RLwas obtained for reconstituted specimens, despite the differences in relative density Drand fines content Fc, quite contradictory to the current liquefaction potential evaluation practice. Then a small amount of cement was added to fines in the sand specimens to simulate a geological aging effect in a short time. It was found that the liquefaction strength RLincreases with increasing Fcmore than the penetration resistance qt, resulting in higher liquefaction strength under the same cone resistance. Thus it has been clarified that not the fines content itself but the aging effect by cementation, which becomes more pronounced in sands with higher Fc, can facilitate reasonable basis why liquefaction strength is modified with increasing fines content in the evaluation practice. In addition to the accelerated tests on the reconstituted specimens with cement, intact samples recovered from in situ Pleistocene and Holocene deposits with known ages have been tested and confirmed the similar trend to the above-mentioned results. © Springer International Publishing Switzerland 2014.