抄録
Resulting from application of irregularly repeated loading over a long term period, an appreciable plastic displacement has often been observed in grounds and earch structures. In the present paper, a method for predicting this kind of plastic strain of soils under repeated loading is pursued using triaxial and modified oedometer tests. In the first half part of the paper, time-dependent deformation characteristics were examined through the repeated triaxial tests on a compacted sandy soil. Test results show that the deformation of soil due to repeated loading is fairly attributed to the plastic strain. Except at the beginning and in the vicinity of the failure region of number of load cycles, the ratio of plastic strain to total strain is extremely increased in the logarithm of number of load cycles. In the latter part, specially devised oedometer tests and triaxial creep tests under repeated loading were performed on various kinds of remolded and undisturbed cohesive soils. Arranging these test results, an approximate law was found out for the plastic strain performance. This law seems to be independent of the kind of soils and the loading conditions, and, therefore, to be common with the deformation of compacted sandy soil previously used. A method for predicting the converged strain for soil specimens under repeated loading is proposed making use of this simplified law. Since the converged strain by an extrapolation is particularly governed by the load increment ratio and the frequency of repeated loading, the diagram relating the converged strain to the load increment ratio as a parameter of frequency is suggested to be most practically useful in the prediction of settlement induced by repeated loading.
