The comparison of alternative construction methods is one of the principal reasons for using simulation to model construction processes. The efficiency and effectiveness of such comparisons can be greatly improved by the prudent use of "matched pairs," a variance reduction technique based on dedicated and fully synchronized random number streams. The basic methodology is illustrated by using the Stroboscope simulation system to compare two alternative construction methods for rock tunneling (Conventional vs. the NATM). For this example the effects are dramatic. The probability of choosing the less expensive construction method based on a single run increases from 55% to 96%, the variance of the difference in cost decreases by two orders of magnitude, and the 95% confidence interval for the expected difference in cost given by 4,000 independent pairs is given by only 7 matched pairs.

Photios G. Ioannou & Julio C. Martinez
Civil & Environmental Engineering Department
University of Michigan
Ann Arbor, Michigan 48109-2125, U.S.A.
e-mail: photios@umich.edu

STROBOSCOPE, construction, simulation, modeling, tunneling, NATM, variance reduction, random number streams, common random numbers, design of experiments, comparison of alternatives.