Abstract
In Japan, there are many man-made sandy strata of hydraulic fill in recent years. But little is known about the mechanical properties of the undisturbed samples of these sands at present. Density measurements and triaxial compression tests have been performed on undisturbed specimens of sand in order to determine the mechanical properties of hydraulic fill. Undisturbed samples of sands have been taken from block samples at Ichikawa and core samples by freezing at Chiba.
Both hydraulic fills are poorly-graded fine-sands on the basis of boring logs and sieve analysis. Dry densities from small specimens of these sands show much irregular variation with the depth. Avdrage dry densities of sand of hydraulic fills are over 1.4g/cm3 that is nearly those of middle Pleistocene deposits. Relative densities of hydraulic fills are the same or slightly smaiier than those of Holocene deposits.
The stress-strain curves for undisturbed and disturbed (remolded) samples by triaxial compression tests are compared as follows. The axial strain at failure for undisturbed sand is lower than that Jor disturded sand. The maximum deviator stress, the maximum compression of volumetric strain and the secant modulus for undisturbed sand are higher than those for disturded sand. Characteristics of dilatancy by triaxial compression tests on sample Ichikawa B from hydraulic fill is as follows. Here, the value of stress dilatancy κf is defined as a ratio of effective stress ratio to dilatancy factor at failure. The value of κf for disturbed samples increases with increasing confining pressure. For the undisturbed sands, a minimum value of κf is found at a confining pressure of about 0.2kg/cm2. In the range of confining pressures lower than about 0.2kg/cm2, the value of κf increases with decreasing confining pressure, the trend being contrary to that of disturbed sand. And these similar results are found in samples from Quaternary sand deposits which have unconfined compressive strength. However, sample of Ichikawa B has no unconfined comressive strength when saturated. In spite of the fact that the sand from hydraulic fill has not passed ten years yet, some difference in triaxial compressive properties exists between undisturbed and disturbed samples. And the triaxial compressive properties of undisturbed samples from hydraulic fill are like those from Quaternary deposits.
