Statistical evaluation and calibration of two methods for predicting nail loads of soil nail walls in China

Abstract

The design of soil nail walls in China is dictated by two national technical specifications, namely, Technical Specification for Retaining and Protection of Building Foundation Excavations by China Academy of Building Research (CABR) and Specifications for Soil Nailing in Foundation Excavations by China Association for Engineering Construction Standardization (CECS). Each specification proposes a method for computation of maximum nail loads while the prediction accuracy of the method is still not yet fully assessed. To fill the gap, this study evaluates the accuracies of the two methods using 144 measured nail loads collected from fully instrumented soil nail walls in China. The influences of three wall working conditions on the prediction accuracy of the methods are also examined. The results show that the two default methods overestimate the maximum nail loads by about 40% on-average and the spread in prediction generally ranges from 70% to 100%. However, the prediction accuracy is not significantly influenced by wall working conditions. Simple calibrations with two or three empirical constants are introduced to the two methods to achieve great improvements in prediction accuracy. The calibrated CABR and CECS methods are demonstrated to be unbiased on average and the prediction dispersions are reduced to about 50%.