PREDICTION OF CYCLIC UNDRAINED STRENGTH OF SAND SUBJECTED TO IRREGULAR LOADINGS

概要

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Methods of predicting the cyclic undrained strengths of normally consolidated saturated reconstituted sand subjected to irregular loadings from those subjected to uniform loadings are discussed based on the results of torsional shear tests on hollow cylindrical specimens of two kinds of sands. Two time histories of acceleration at the ground surface during earthquakes were used as input irregular loading patterns. A new method to account for the difference in liquefaction strength between uniform and irregular loadings is proposed. In this method, the liquefaction strength against uniform loading is represented by the critical number of loading cycles (N_c)_<cr>. (N_c)_<cr> is defined as the number of loading cycles at which the strength curve representing the relationship between the cyclic stress ratio and the logarithm of the numver of cycles N_c to liquefaction has the maximum curvature. It was found that the liquefaction strength against a given irregular loading pattern represented by the maximum single amplitude of cyclic shear stress is a linear function of the logarithm of (N_c)_<cr>, whereas the slope depends on the wave form. Furthermore, the cumulative damage concept was found useful to predict whether or not a given sand element fails against a given time history of cyclic shear stress series when the strength curve for uniform loadings is given for this element.
社団法人地盤工学会の論文
1986-06-15