USE OF SHOTCRETE FROM THE STANDPOINT OF THE CONTRACTOR

The requirement is emphasized of proper materials handling. The contractor discusses past experiences citing past mistakes and their resulting lessons. These include the requirements for extending the shotcrete lining to the invert in lieu of springline in the bad ground, the necessity for evaluating instrumentation data expeditiously, and the detrimental effect of wire mesh reinforcement. The case is also cited of the successful and advantageous use of sodium silicate in the mix. The mistakes outlined here include an attempt to automate the shotcrete application, and an attempt to advance the tunnel into faulted area without increasing the peripheral area of shotcrete coverage. A tunnel project is described which went through live faulted area where line points kept moving from day to day. Ribs were placed on three foot centers which allowed spilling. The tails then cut off the spilling and shotcrete was used to fill in between the ribs. This gave the required strength as well as enabled a reasonable rate of advance. Shotcrete was also used in the crown while digging ahead of the breast boards. The ability to get it to the right place at the right time is seen as the greatest problem with shotcrete. Other aspects discussed include the ability to shotcrete without slowing down the heading in tunnels, the technically made nature of shotcrete and its supervision by experts, and a railroad tunnel project in rock of volcanic material.