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Indentation Tests to Investigate Ice Pressures on Vertical Piers

  • K. R. Croasdale (a1), N. R. Morgenstern (a1) and J. B. Nuttall (a1)

Abstract

Controlled field and laboratory tests were performed to investigate the relationship between ice strength and the maximum ice pressures on vertical piers. The apparatus used in the field tests consisted of a flat indentor (75 cm wide) which was pushed through the ice by hydraulic rams. 27 tests were conducted on lake ice up to one metre thick. Ice pressures in the range 2.5 to 5.0 MPa were obtained for ice in good initial contact with the indentor. The ice pressures exhibited little sensitivity to variations in temperature, ice thickness and strain-rate for the range 7.5 × 10-7 to 4.4 × 10-3 s-1.

The average unconfined compressive strengths obtained in the laboratory were about 20% higher than the average field ice pressures. In addition, the laboratory strengths were found to be sensitive to temperature, and to strain-rate in the range 1 × 10-7 to 1 × 10-3 s-1. The confined compressive strength was two to three times the unconfined strength.

The failure modes observed in the indentation tests were similar to those predicted (before the tests) by an upper-bound plasticity model. The ability of the model to relate small-scale ice strength to field ice pressures is discussed.

Résumé

Tests à l’indentateur pour mesurer les pressions dans la glace des piles verticales. Des contrôles sur le terrain et des essais en laboratoire ont été conduits pour déterminer la relation entre les contraintes dans la glace et les pressions maximum sur les piliers verticaux, L’appareil utilisé sur le terrain consistait en un indentateur plane (75 cm de large) qui était poussé à travers la glace par un piston hydraulique. Vingt sept essais furent menés sur de la glace de lac allant jusqu’à un mètre d’épaisseur. Des pressions de glace de l’ordre de 2,5 à 5,0 MPa ont été obtenues pour la glace lorsque le contact initial avec l’appareil était bon. Les pressions dans la glace se sont montrées plus sensibles aux variations de la température, de l’épaisseur de la glace et de la vitesse de déformation entre 7,5 × 10-5 et 4,4 × 10-3 s-1.

Les résistances moyennes à la compression hors enceinte, obtenues en laboratoire, étaient d’environ 20% supérieures aux pressions dans la glace sur le terrain. De plus, on a trouvé en laboratoire des résistances de l’ordre 1 × 10-7 et 1 × 10-3 s-1. La résistance à la compression avec enciente était deux ou trots fois plus forte que hors enceinte.

Les modes de ruptures observées clans les essais à l’indentation ont été semblables à ceux prévues (avant le test) par un modèle à la limite supérieure de la plasticité. La capacité du modèle à trouver une relation entre la résistance de la glace à petite échelle et les pressions dans la glace sur le terrain est discutée.

Zusammenfassung

Prägeversuche zur Untersuchung des Eisdrucks auf senkrechte Ufermauen. Zur Untersuchung der Beziehung zwischen der Eisfestigkeit und dem maximalen Eisdruck auf senkrechte Ufermauern wurden kontrollierte Feld- und Laborversuche durchgeführt. Das Gerät für die Feldversuche bestand aus einem flachen Prägestempel (Breite 75 cm), der mit hydraulischen Rammen durch das Eis gepresst wurde. 27 Versuche erstreckten sieh auf See-Eis bis 1 m Dicke. Es ergaben sich Eisdrucke im Bereich von 2,5 bis 5,0 MPa für Eis in gutem Anfangskontakt mit dem Prägestempel. Der Eisdruck erwies sich als wenig abhängig von der Temperatur, der Eisdirke und der Verformungsratc im Bereich von 7,5 × 10-5 bis 4,4 × 10-3 s-1.

Ohne Eingrenzung ergab sich die mittlere Druckfertigkeit im Labor um etwa 20% höher als der mittlere Eisdruck im Feld. Ausserdem zeigte die Festigkeit beim Laborversuch Abhängigkeil von der Temperatur und der Verformungsrate im Bereich von 1 × 10-7 bis 1 × 10-1 s-1. Unter Eingrenzung war die Druckfestigkeit zwei- bis dreimal höher als ohen Eingrenzung.

Die bei den Prägeversuchen beobachteten Brucharten waren ähnlich denen, die vor den Versuchen mit einem Plastizitätsmodell vorhergesagt wurden. Es wird die Eignung des Modells zur Extrapolation von kleinmasstäbigen Eisfestigkeiten auf Eisdrucke im Feld diskutiert.

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References

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Croasdale,, K. R. 1974. Crushing strength of Arctic ice. In Reed,, J. C, and Sater,, J. E., ed. The coast and shelf of the Beaufort Sea. Proceedings of a symposium on Beaufort Sen coast and shelf research. Arlington, Virginia, Arctic Institute of North America, p. 37799 .)
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Indentation Tests to Investigate Ice Pressures on Vertical Piers

  • K. R. Croasdale (a1), N. R. Morgenstern (a1) and J. B. Nuttall (a1)

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