Many long tunnels are under construction or planning in Korea. For these long tunnels, reducing the construction period is very important in the economical aspects. To speed up the tunnel construction, studies are devoted to excavation techniques like long hole blasting, full face driving or mechanical excavations. In this study, authors designed new concrete form to shorten the concrete lining period. Normally it takes long time to install and dismantle the lining forms. It was improved by adopting air insulting rubber. Other devices were suggested like reinforced window to check the filling situation of the concrete milk and attached vibrators of low velocity to harden the concrete during pouring. On the other hand, distance between the blasting face and lining was minimized considering the safe limit of vibration of concrete lining. Effect of blasting vibration on the curing concrete was investigated. Optimal distance was suggested considering the curing time of concrete lining. It was proved that more than 15 % of construction period was shortened by these techniques.
Most tunnels were excavated by NATM method. Normally concrete structures like concrete lining were constructed after blasting excavation. It is because blasting vibration can make cracks in concrete lining and lower the strength of lining. In case that installing concrete lining after excavation, construction period will be delayed. It is desirable process control that constructing excavation and installing lining concurrently. In this study, authors designed new concrete form to shorten the concrete lining period. Other devices like reinforced window to check the filling situation of the concrete milk and attached vibrators of low velocity to harden the concrete during pouring were suggested. On the other hand, distance between the blasting face and lining was minimized, considering the safe limit of vibration of concrete lining. Effects of blasting vibration on the curing concrete were investigated. Optimal distance was suggested considering the curing time of concrete lining.
Normally it takes long time to install and dismantle the lining forms. It is because installation and dismantlement of cast for lining form is performed by hand. It was improved by adopting air insulting rubber (Fig. 1). It takes two hours to install cast for lining forms by five workers. Through improving working methods and facilities (Fig. 2), it is possible to install and dismantle cast in 30 minutes by minimum workers.
The vibrator is used to maximize the efficiency of concrete filling. Minimum volume is adopted to reduce the incidence of one vibrator for intercepting movement and deformation of lining form. Suitable range of vibrator is 1 m and vibrator is installed in height and length direction (Fig. 3). This also can reduce the number of workers and improve the efficiency by inputting vibrators through windows for checking the filling situation of the concrete milk.
