The development and implementation of a tunnel characterization method

The Garner and Coffman method was developed to design a proposed underground facility based on an allowable settlement profile; the method may also be used to characterize an unknown underground facility based on an observed surface settlement profile. The method uses both static methods and 2-D finite element analyses to relate the characteristics of the ground surface settlement profile to the underground facility (depth, diameter, and number of tunnels). The calibration and validation of the Garner and Coffman method, as obtained by using tunnel segment data from historical tunneling projects (Bangkok, London, Taipei, Singapore, and Heinenoord), are presented. Specifically, the method was calibrated using settlement profiles and facility characteristics from 15 tunnel segments and validated using settlement profiles from 16 additional tunnel segments. A numerical relationship (developed during this research project) was then used during the validation of the model to predict facility characteristics for the “unknown” underground structures. The predicted depth and diameter for each of the “unknown” underground structures were within ten percent of the actual diameter and actual depth of the underground structure, as obtained from the literature. For all 16 validation tunnel segments, the tunnel location was predicted within one tunnel diameter of the actual facility centerline.