DYNAMIC TESTS OF MODEL EARTH DAMS

Abstract

According to the results of field experiments, agar-agar model tests and some theoreticalconsiderations, on which some paper have been already published by the author (1957, 1959 and1962), the vibration should be considered to be a two-dimensional one, taking vertical as wellas horizontal displacements into consideration. In addition, the tests of model dams, which weremade of mixed cement, wheat flour and machine oil and fixed on the shaking table, showed thefact that the first cracks were developed perpendicular to the dam slope near the bases ofdams and the second cracks followed the first and so on, until the dam body was broken down.The cracks in early stages would be caused by the tensile stresses near the surface of the dam.Now, the tests of model dams, which were made of four kinds of materials composed ofmixed sand, wheat flour and machine oil, were made so as to obtain some information aboutthe breaking conditions of earth dams. In order that the results of the model tests shouldrepresent correctly the earthquake responses of the prototypes, it was necessary to consider therequirements of model similitude. According to the results of the similitude analysis for thiscase, it has seen that the density of the materials should be larger on the model than on theprototypes, on the other hand its shearing strength should be smaller on the model than on theprototypes. It was difficult that all required model values have been achieved. The results ofthese tests were as follows:(1) When the unit weight and the angle of internal friction of the materials of modeldams became small and its cohesion became large, the first cracks were clearly developedperpendicular to the dam slope near the bases of dams.(2) The larger the unit weight and the angle of internal friction of the materials of damsbecame, the easier the failure of a mass of the materials, which was called a slide, occurred.(3) The vibrational intensity that the first cracks appeared on the surface of the dam body, increased with a decrease of the dam slopes.(4) ln the models of the same slopes, the first cracks appeared at the vibrational inten-sity that was proportional to the period.