Abstract
The authors conduct cyclic torsional shear tests to evaluate the effect of the long shaking on the occurrence of liquefaction. Silty sand taken from the boiled sand Urayasu City and Toyoura sand were tested under three densities, loose, medium dense and dense. Two types of shear wave were applied to specimen, i) sine wave of 20 cycles and ii) the seismic wave recorded during main shock and after shock of the 2011 Great East Japan Earthquake at Urayasu K-NET. Test results, showed that the influence of the long seismic wave on liquefaction strength was greater than the design standards shown to Japan Road Association. Moreover correction factor CW according to the JRA standard increased with liquefaction strength. Based on the test results, safety factor against liquefaction FL at Takasu Elementary School where liquefaction occurred during the Great East Japan Earthquake was estimated. The estimated FL showed that reclaimed sand liquefied by the earthquake thought the maximum surface acceleration was not large.
