Costing Contingencies

by P. E. Sperry, Tunnel Construction Consultant; 21318 Las Pilas Road, Woodland Hills, CA 91364,

Serial Information: Civil Engineering—ASCE, 1988, Vol. 58, Issue 4, Pg. 68-69

Document Type: Feature article

Abstract: Estimating the cost of constructing a tunnel is an art rather than a science. The unknowns are too great to predict costs relianblbly. On the other hand, owners need cost estimates in order to decide whether to proceed on a proposed tunnel, and if so, how to judge bids. The author proposes and outlines a rational method of cost estimating, in which contingencies for are evaluated at each stage of the design process. Among them are factors as subjective as the reputation of the owner for obstructing construction progress. The method also supposes a percentage figure for the contractor's experience, and looks at the state of tunneling and the number of contracts being awarded at a given time. Numbers become more specific as the design proceeds to the more detailed stages. Negative contingency numbers are assigned to contract documents that assume part of the contractor's risks. Design contingencies, for example, take unexpected changes into account.

Subject Headings: Construction | Costs | Estimation | Tunnels |

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