Citation

Grice H, Durand M. Transp. Res. Rec. 1979; 733: 51-56.

Copyright

(Copyright © 1979, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

The economic construction of transportation projects depends in part on the availability of all relevant geological and geotechnical data. In Montreal, Canada, all of the 120 km (75 miles) of subways, major sewers, and aqueducts constructed during the last 18 years have been affected by local geological factors. Contracted costs for subway tunnels in shale were about 20 percent higher than for those in limestone. Locally, the presence of weathered zones in limestones and shales, where they have been faulted or intruded, increased actual costs to six times the normal unit price in good limestone. The contracted cost was 12.5 times the normal for a transition from an open cut into a tunnel in soil or rock. Variations of costs for contractors were estimated from rates of advance, amounts of concrete required to backfill overbreaks, and numbers of steel arch ribs used for roof supports. Tunnel-boring machines were more sensitive to geological surprises than were normal construction methods. Comparisons were made between data from preconstruction investigations and both construction records and site mapping. It was confirmed that, although preconstruction data usually give general warning of problems, precise notice is often lacking. Even the use of techniques such as the measurement of rock-core lengths gives only a partial indication of actual tunneling conditions, which emphasizes the need for continuous detailed mapping during construction.