Experimental studies on collapse prediction of Shirasu slopes in consideration of the variation of shearing resistance and infiltrationflow caused by various rainfalls on earthquake

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A series of undrained cyclic and monotonic triaxial tests has been performed on a volcanic soil "Shirasu" which has crushable particles. Testing was performed on loose and dense specimens and the results were compared with those of Toyoura sand. As a result, the undrained cyclic and monotonic shear behavior of "Shirasu" is found to be greatly dependent on the confining pressure and its density.In-situ tests for measuring unsaturated permeability of Shirasu are carried out by means of two methods. The first is the method that measures the variation of infiltration rates from the doublering infiltrometer. The other is one that does the variation of water depth in the recharging holes. Unsteady infiltration in the tests are numerically simulated to identify the parameters of Mualem's equation. The parameters are also identified from the laboratory test values that measured from the undisturbed soil. These results are compared and confirmed to be coincide with each other. However, evident difference is revealed in the numerical simulation ; i.e. the computation for the recharging hole needs great amount of running time. From the results, it is cleared that infiltration test with infiltrometer is easy handling and useful method for the measurement in many locatins.