Tunnel Boring Machine Technology for a Deeply Based Missile System. Volume I, Application Feasibility. Part 1.

Technical feasibility and cost studies were made for a deep-based missile DBM tunnel system Mesa concept by means of tunnel boring machines TBMs, along with designing an egress machine for post-attack tunneling through approximately 2,500 feet of probably unstable rock to the rubble zone. Currently, available designs of TBMs are readily adaptable for the conventional excavation in geologic environment considered suitable for DBM siting. Most, if not all, of the tunnel sections in the rocks of anticipated structure and strength will require support varying from simple rock bolting to concrete segments. Current 1979 costs for similar tunnels Chicago vary from 600 to 800 per linear foot of tunnel, while the estimated costs for the DBM tunnels average as high as 1,600 per foot because of the greater depths, weaker rock, longer tunnels, possible remoteness geographically, and other related factors. Two concepts for egress machines have been proposed by the Robbins and Jarva companies. The details of use of geotechnical data are given in Appendix A and were qualitatively for estimates of support requirements and costs. The only calculation that could be made based upon available data was the assumption that squeezing ground would occur if the stress concentration at the ribs of the tunnels exceeds the unconfined compressive strength. Average conditions assumed for the tunnel calculations in the COSTUN program automatically include the effects of rock quality designation RQD, etc.