The Relationship Between Rockfall and Shocks from Blasting

Abstract

The relationship between rockfall and vibration of the ground has never been fully analyzed before in Japan because of several problems which fall within one of two categories which we have labelled “motivecause” and “primary cause”.
Problems falling within the “motive cause” category are concerned with characteristics of vibration whilethose problems falling within the “primary cause” category are concerned with the conditions of mountainslopes (e. g. morphometric parameters of slope; shape, size and depths at which blocks have been buried onslopes ; quality of weathered materials and surface soil).
In spite of these problems, it is quite important to analyze the relationship between rockf all and vibrationof the ground for some kinds of construction works such as railway and tunnel construction because shocksfrom blasting may cause rockfalls.
In our survey, two seismic tests were carried out-one involving a dynamite blast and the other involvinga shockwave caused by a passing train.The results of these tests can be summarized as follows:
1. The shock that was produced by the passing train did not cause a severe rockfalls. The maximum deformationof the ground was 7.6-10^-5 cmand occurred above 10 seconds. These results are too small tocause a rockf all.
2. The relationship among the amount of dynamite, the maximum displacement, the maximum accelarationand the transmissive velocity of vibration was studied to find the point at which a severe rockfall waslikely to occur during tunnelling work.In this test, 3 kg of dynamite were exploded 50 meters from the test site. As a result, the maximumdisplacement was 1.4-10^-3 cm. This value is also too small to cause a rockfall.