Statistical analysis of test data on unbound aggregate layers at experimental site

Abstract

The field performance of unbound aggregate layers was investigated using an extensive program of light weight deflectometer (LWD), air permeameter (APT) and nuclear density tests on two testing strips, one on untreated subgrade and the other on cement-treated subgrade, constructed at an experimental site. The main objective was to examine the use of LWD and APT for control of the state of compaction and hydraulic conductivity of aggregate layers commonly used as roadway subbase draining or filter/separation layers. The test strips construction and the testing program are described, and test results are discussed. Statistics and correlation studies of the collected data, as well as Bootstrap resampling simulations are presented and serve as a basis for assessing the testing methods and the influence of statistical sample size on the reliability of QA/QC outputs. The main outcomes address the spatial variability in the measured properties, the evaluation of materials and methods used to construct the strips, and the methods used for characterising the layers. These highlight some limitations in current quality assurance guidelines and suggest a risk-informed approach.