Settlement calculation and back-analysis of soil properties for large test embankments on soft clay deposits, Windsor, Ontario, Canada

Marjan Oboudi, Raymond Hache, Gwangha Roh

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Dams and Embankments

ABSTRACT: Details of a comprehensive settlement monitoring program and interpretation of field measurements at the project site located in Brighton Beach, Windsor, Ontario, are presented in this paper. The settlement monitoring program (carried out by others) consisted of constructing two large test embankments built in stages and instrumented with Settlement Monitoring Plates (SMPs), and Vibrating Wire Piezometers (VWPs), to monitor the behavior of the underlying thick soft clay deposits presented at the project site. Conventional settlement analyses were conducted to interpret the field measurements of pore water pressure and settlement, and consolidation parameters were calibrated. The calibrated soil parameters were used to estimate the amount of settlement associated with the anticipated utility construction with grade raise at the project site. Available field measurements from previously studied test embankments within and in the close vicinity of the project site were also considered for a comparison purpose.

RÉSUMÉ: Ce document traite d™un programme complet de surveillance de tassement sur un site de projet situé à Brighton Beach, Windsor, en Ontario. Le programme de surveillance de tassement portait sur la construction de deux importants remblais d™essai, construits par phases et équipés d™un système de surveillance comprenant des plaques de tassement et des piézomètres à fil vibrant. Celui-ci suveille la performance des dépôts sous-jacents d™argile molle présents sur le site du projet. Des analyses théoriques ont été menées pour interpréter les mesures de la pression d™eau interstitielle et du tassement prises sur le terrain. Par la suite, des paramètres de consolidation ont été rétrocalculés. Les données issues de cette analyse ont été utilisées pour estimer l™ampleur du tassement associée à la construction de services publiques et au rehaussement du niveau du sol sur le site du projet. Des comparaisons ont été effectuées à l™aide des mesures prises sur le terrain à partir de remblais d™essai préalablement étudiés sur et à proximité du site du projet. INTRODUCTION The performance of two instrumented test embankments was monitored and investigated as part of the planned Gordie Howe International Bridge in Windsor, Ontario. The results of the tests and field measurements are discussed and interpreted in Finite Element (FE) framework as well as conventional Consolidation Theory to reproduce the distribution of settlements and pore water pressure under the test embankments. The calibrated soil models will be utilized to estimate the amount of settlement associated with the planned utility construction with grade raise at the project site. The site is situated in the physiographic regions known as the flClay and Sand Plainsfl, which consist of a series of shoreline deposits along the west and north shores of Lake Erie. The site subsurface condition is predominantly Lacustrine and Glaciolacustrine deposits. The soils typically consist of silt and clay and minor sand. The general stratigraphic series of the zone is usually divided into three units: (i) surficial granular soils layer composed primarily of sand and silt; (ii) thick layer of plastic clays and silts, and (iii) lower layer of sandy silt glacial till underlain by dolomite limestone bedrock. There is also some fill at the surface of variable thickness. Based on the geotechnical investigation findings at the site, the lower part of the clay layer has been nearly normally-consolidated (1) to slightly under-consolidated (<1). Given the age of the clay deposit, it is unlikely that the deeper clays are under-consolidated unless there has been a progressive lowering of the piezometric head at the site. It is conceivable that the artesian pressure within the bedrock has been abating with time, as a result of climate change and that the piezometric pressures within the clay profile have correspondingly been lowering. Regardless of the geological cause of the state of the deeper clay layers, it is anticipated that any additional loads to the site will trigger some degree of primary and secondary consolidation within the deeper clay layers. PRELOAD TEST The test embankments extended over an area of approximately 1000 x 300 square meters (which includes Zones 4-2A, 4-2B, and 4-3) and an area of approximately 500 x 500 square meters (which includes Zone 1) as shown on Figure 1. A width of 500 to 1000 meters ensured that a significant stress increment reached the deeper part of the clay soils layer. Note that the focus of

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