Identifying the Mechanisms of Ice Lens Formation Through Soil Suction Measurement and PIV Analysis During Step Freezing Tests

Heidi McKnight-Whitford, Andy Take, Craig Lake

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Soil Mechanics

ABSTRACT: The role of soil suction, in the development of ice lens formation in soils, is one process that has been postulated to contribute to water migration in freezing soils but very few studies have accurately measured suction development during the freezing process. The objective of this research is to develop several simultaneous testing techniques to measure suction, axial strain, temperature gradients, water migration, frost front location, and frost heave in a clay undergoing freezing in a one-dimensional, open, step-freezing condition. In the paper, the development of the testing techniques is described with particular focus being placed on the use of modified high capacity pressure transducers to accurately and reliably measure high soil suctions as well as the calculation of axial strain/void ratio using Particle Image Velocimetry (PIV) during the test. RÉSUMÉ Le rôle des sols d'aspiration, dans le développement de lentille de glace formation dans les sols, est un processus qui a postulé pour contribuer à la migration d'eau dans les sols gel mais très peu d'études ont mesuré précisément développement d'aspiration pendant le processus de congélation. L'objectif de cette recherche est de développer simultanément plusieurs techniques de test pour la mesure, aspiration axiale strain, gradients de température, l'eau, la migration avant le gel, emplacement et soulèvement dû au gel dans une argile subit le gel dans un unidimensionnel, ouvert, étape gel condition. Dans le papier, le développement des techniques de test est décrite avec un accent particulier mis sur l'utilisation de modifiés haute capacité les transducteurs de pression de mesurer de façon précise et fiable mesure haute aspiration du sol ainsi que sur le calcul de traction axiale/void ratio aide Image Particules, rugosimétrie (PIV) au cours de l'essai. 1 INTRODUCTION Frost heave of soil cover and barrier systems for waste containment applications can cause internal damage, leading to hydraulic performance related issues. Problems encountered include increased effective void ratio and hydraulic conductivity of the barrier system (Benson et al. 1995) and the potential for contaminant release into the environment. Frost heave is also responsible for damage to buildings and other civil engineering infrastructure, when not accounted for properly (Andersland and Anderson 1978). The objective of this paper is to develop a laboratory freeze cell device and procedure to measure suction development during frost heave damage in clayey material specimens as well as use Particle Image Velocimetry (PIV) to identify the temporal distribution of ice lens formation. The experimental apparatus and test methodology are presented and their validity confirmed through obtaining repeatable test data. 1.1 Suction and Its Role in Ice Lens Formation When frost susceptible soils are subjected to sub-zero temperatures, they undergo pore water freezing and subsequent heave due to ice lens formation. When pore water freezes in the soil, a suction gradient develops that induces water migration from the unfrozen soil, through the frozen fringe, where it accumulates and freezes. The frozen fringe, which acts as a zone of impeded flow caused by the partial freezing of pore water, is a frozen zone of soil located between the active ice lens and the unfrozen soil (Nixon 1991). Water migrates through the frozen fringe in a thin layer of unfrozen water that remains close to the soil particles. During freezing, water undergoes a nine percent expansion, initiating heave in the soil (Konrad and Morgenstern 1980). Large suctions can develop in a soil during freezing at the ice-water interface at the freezing front. Measuring and understanding these suction values are important for understanding processes that take place during the freezing of a soil such as water migration, freezing induced consolidation, and segregation potential. Suction that develops in the frozen fringe is the driving force of water migration (Konrad and Morgenstern 1980). Konrad and Morgenstern (1981) showed that, for a uniform soil sample, the suction that developed at the frozen fringe was affected only by the warm-side temperature. Konrad and Morgenstern (1982) predicted that the suction at the frost front of Devon silt could not exceed -80 kPa, without cavitation. In past research, attempts at measuring soil suction have largely been made using tensiometers which are

RÉSUMÉ: ntifying the Mechanisms of Ice Lens Formation

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Cite this article:
Heidi McKnight-Whitford; Andy Take; Craig Lake (2014) Identifying the Mechanisms of Ice Lens Formation Through Soil Suction Measurement and PIV Analysis During Step Freezing Tests in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper435,author = Heidi McKnight-Whitford; Andy Take; Craig Lake,title = Identifying the Mechanisms of Ice Lens Formation Through Soil Suction Measurement and PIV Analysis During Step Freezing Tests,year = 2014}