Use of the ranking distance as an index for assessing the accuracy and precision of equations for the bearing capacity of piles and at-rest earth pressure coefficient

In many geotechnical design situations, a number of different calculation models have been developed to predict the value of a particular quantity required for use in design calculations, for example, the bearing capacities of driven and root piles, and K0, the at-rest earth pressure coefficient. In this paper the authors show how the dependability of different calculation methods can be compared and assessed using a synthetic probabilistic approach and the ranking distance (RD) index. Measured values, Qmeas, are compared with calculated values, Qcalc, using the "bias factor," defined as the ratio Qmeas/Qcalc. The bias factor values obtained using a particular calculation method are processed to evaluate the "accuracy" and "precision" by calculating a central tendency and a variability statistical parameter, respectively, from the values. The RD index is a comprehensive statistical parameter for assessing the dependability of a particular calculation method and is based on the central tendency and variability. Using the ratios between calculated and measured bearing capacity and earth pressures values, the RD index is used to assess the accuracy and precision of the most frequently used pile driving formulae, two equations for the bearing capacity of root piles, and seven equations for the at-rest earth pressure coefficient.Key words: accuracy, precision, probabilistic approach, ranking distance.