Comparative Cost of Near Surface and Deep Tunnels

摘要

Comparative cost estimates are presented for deep and shallow tunnels constructed under geologic conditions that are found in major U.S. urban areas. The cost data presented can be used in the pre-design planning of tunnel systems for sewer, water, utilities, and transportation. Particular emphasis was placed on the potential for reducing the overall cost of tunnel projects in urban areas by placing tunnels at greater depths where geologic conditions are more favorable and disruption of the surface environment is avoided. The cost analyses were performed using COSTUN, a comprehensive computer program for estimating the cost of soil and rock tunnels. The geologic conditions assumed for the analysis were modeled after the known conditions in Atlanta, Boston, Chicago, Denver, and Los Angeles. Results of the cost comparison are: (1) the cost of deep underground heading tunnels is much more sensitive to different geologic conditions than is the cost of cut and cover tunnels; (2) for tunnel sizes less than 6 to 10m, deep rock tunneling is less expensive than cut and cover construction; (3) the cost difference between rock tunneling from underground heading and cut and cover construction decreases with tunnel size with the cost of both types of construction being nearly the same for tunnels in the 10 to 12m size range; and (4) the cost of underpinning, utility relocation, and surface restoration associated with cut and cover construction is extremely variable and can sometimes exceed the cost of the basic tunnel construction.