Abstract:

The requirements on the initial strength of shotcrete in different countries, as well as related studies made in Japan, are presented. It is emphasized that the measurement of the initial strength of shotcrete must be strengthened in tunnel construction so as to accumulate data on the initial strength of shotcrete and acquire the correlation between the initial strength of shotcrete and the control of the deformation. It is stated that the optimum mixing ratio of shotcrete is the key to ensuring the quality of shotcreting. The flowchart of the trial to determine the optimum mixing ratio of shotcrete proposed in Japan is presented, and it is proposed that shotcreting production line should be established. The development and application of shotcreting machines (including separated shotcreting system, integrated shotcreting system, longboom shotcreting machine, and shotcreting machine with double nozzles) in foreign countries, especially in Japan, are presented in detail. It is believed that improving the mechanization level of shotcreting operation and performing rapid and timely shotcreting are very important for the tunneling safety and the shotcreting quality. The stateofart of fiberreinforced shotcreting in different countries is presented. It is believed that proper reinforcing materials can replace the wiremesh and that fiberreinforced shotcreting should be tried so as to simplify the shotcreting procedure and improve the speed and quality of shotcreting. The results of the 40year investigations made on the durability of the shotcrete of Seikan tunnel in Japan are presented and conclusion is drawn that the shotcrete of Seikan tunnel has good longterm durability. Finally, it is emphasized that study on the shotcreting technology and development of shotcreting equipment are the main present tasks and how to ensure the initial strength of the shotcrete and how to establish the shotcreting production line are the main topics in the future.

Key words: tunneling, mining method, shotcreting, initial strength, mixing ratio, mechanization, fiberreinforced shotcrete, durability