Undrained behaviour of near-saturated sand in cyclic and monotonic loading

Multiple series of undrained triaxial tests were conducted on nearly saturated specimens of clean sand under monotonic and cyclic loading conditions. In each series of the tests, the relative density was varied from 5 to 70% and the degree of saturation was changed from 0.1 to 0.95 in terms of the B-value. The outcome of the monotonic loading tests disclosed that, while the shear strength tends to increase with decreasing B-value in loose state of packing, the strength of sand becomes reversely smaller with decreasing B-value if the density is high. Regarding the cyclic loading tests, the results revealed that the cyclic strength tends to increase apparently with decreasing level of saturation for the loose sand. It was found, however, that for the relative density in excess of about 80%, this tendency is reversed leading to the decrease in the cyclic strength with decreasing B-value. This anomalous behaviour is properly interpreted in the light of the test data obtained in the monotonic loading test.