A statistical approach is introduced herein for obtaining representative normal distribution curves and computing ground loss and width parameters systematically from field data. Also introduced is a scheme to correct the eccentricity of settlement troughs. Surface settlement troughs over tunnels obtained for Construction Contracts CH218, CH223 and CP262 of the Taipei Rapid Transit Systems were analyzed accordingly and, based on the results obtained, empirical relationships were established for estimating the widths of settlement troughs in the T1, T2 and B2 Zones in the Taipei Basin.