Topographic, geologic and rainfall factors affecting the rate of sediment discharge from steep mountain basin are investigated by analyzing the data of deposited sediment in sediment control dams in mountain area of Northern Kanto, Central Japan. Almost linear ralations can be recognized between average annual volume of accumulated sediment per unit drainage area (qs) and mean gradient of basin (S) in log-log papers with each geological division. It can be derived that the erodibility of plutonic rocks is half as large as that of young volcanic body and four times as large as that of Paleozoic rocks by vertical distances of the regression lines. Computed values by the regression equations of which variables are drainage density (D), valley bed slope of upper reaches of dam (I) and S agree quite well with observed values. By using the close relations between S and qs in short periods when heavy rains occurred, it is inferred that the maximum rainfall intensity for three hours (R3) has the largest effect on sediment yield. The equations for estimating sediment yield of which variables are S, D and R3 are presented.
This paper aims that we clarify the mechanism on the impact-wear and the resistance of the concrete against the impact-load. We have designed a special test-machine to perform this trial. The test-machine has a structure as figuare-1. Lift up the steel balls (φ=52mm, W=590g, HRC= 52-58) autmatically by the chain conveyer and fall them down continuously at 10 times one minuit_ The results are as follows : 1) The phenomena of impact-wear on the concrete surface may be so called the virgin-wear. 2) We are able to test the resistance of the concrete against the impact-load by the Ros-angeles test of aggregates. 3) The resistance of concrete against the impact-load has the nearlly maximum at an age of about 10 or 14 days and is likely increased by the following conditions, (1) to use fine aggregates. (2) to lessen the water-cement ratio. (3) the weight ratio of cement to fine aggregate is the best at from 40-50 %. 4) The resistance of concrete against the impact-load seems to be estimated by the compressive strength.