A Review of Prediction Methods of Primary Consolidation Settlement from Field Monitoring Data During Highway Embankment Construction: Three Case Studies

ABSTRACT: The assessment of the degree of consolidation (U) from monitoring data collected during embankment construction has engineering and contractual implications. Estimating U during construction can be critical to confirm that adequate shear strength gain has occurred during hold periods between lift placements to avoid embankment instabilities, and/or that sufficient settlement has been achieved prior to the end of a preload/surcharge period to maintain conformance with post-construction settlement tolerances. Various methods have been suggested by researchers to estimate the degree of primary consolidation achieved during construction, with two commonly implemented approaches being: a comparison of peak pore water pressure measurements to the measurements at the time of the assessment, and an observational method utilizing available settlement data (Asaoka, 1978). For both approaches, uncertainty exists as to the accuracy of the prediction of degree of consolidation; therefore, it is often necessary to supplement the predictions with engineering judgement when making decisions that could affect construction costs and schedule. Three Ministry of Transportation, Ontario (MTO) highway embankment sites in Northern Ontario are examined where foundation monitoring data was collected throughout embankment construction, the preload or surcharge period has been completed, and the end of primary consolidation settlement has been achieved. The range of error in estimating the degree of primary consolidation at various points in time during construction are explored utilizing pore water pressure data, settlement data in conjunction with the Asaoka method, as well as ‘curve-fitting’ to attempt to match model predictions to monitoring data. Best practices for reducing the uncertainty of the predictions are presented.