Abstract

Short-term strength, damage and healing boundaries for rock salt are experimentally determined and integrated into the Hou/Lux-MDS damage-healing model. This model can be used to describe the mechanical behaviour of rock salt during a damaging process (under high stress to strength ratios) as well as during a healing process (under very low stress to strength ratios with high confining pressure). The development of the damage and the stress to strength ratio in the excavation damaged zone (EDZ) of a storage cavern under a minimum internal pressure as well as the development of the healing of damage and the stress to strength ratio under a subsequent maximum internal pressure are investigated project-related. The results of the investigation make it possible to shift the permissible minimum pressure boundary down, allowing the optimisation of decisive economic characteristics of storage caverns.

RÉSUMÉ

Le comportement court terme, l'endommagement et les conditions de colmatage pour le sel gemme ont ete etudies experimentalement et integres dans le model endommagement- colmatage Hou/Lux-MDS. Ce modèle permet de decrire le comportement mecanique de sel gemme pendant le processus d'endommagement (sous fort rapport contrainte-resistance) et le comportement du processus de colmatage sous très faible rapport contrainte-resistance avec forte pression de confinement. Le developpement d'endommagement et le rapport de contrainte-resistance dans une zone d'endommagee (EDZ) d'une cavite de stockage avec un maximum de pression de soutènement ont ete etudies. Les resultats de cette etude permettent de conclure qu'il est possible de baisser la pression de soutènement, et par consequent d'optimiser les caracteristiques economiques decisives des cavite de stockage.

ZUSAMENFASSUNG

Fuer Steinsalz werden Festigkeits-, Schadigungs- und Verheilungsgrenze experimentell ermittelt und in das Schadigungs-Verheilungs-Modell Hou/Lux-MDS integriert. Damit kann das mechanische Verhalten von Steinsalz sowohl bei einem Schadigungsprozess (mit hohen Ausnutzungsgraden) wie auch bei einem Verheilungsprozess (mit niedrigen Ausnutzungsgraden) beschrieben werden. Projektbezogen werden die Schadigungs- und Ausnutzungsgradentwicklung in der Auflockerungszone einer Speicherkaverne unter einem minimalen Innendruck sowie die Verheilungs- und Ausnutzungsgradentwicklung unter einem anschließenden maximalen Innendruck untersucht. Die Untersuchungsergebnisse erlauben, die zulassige Minimaldruckgrenze nach unten zu verschieben, so dass entscheidende wirtschaftliche Kenngrößen von Speicherkavernen optimiert werden können.

Introduction

It has been determined through laboratory tests, that exceeding the damage boundary under high stress to strength ratios generates, among other consequences, damage, dilatancy and increased creep rates and permeability. However the damage, which already existed in the salt rocks and which developed further due to the stress caused by mining activities, may heal as the healing boundary is undershot under very low stress to strength ratios with a high confining pressure as a result of the stress relief (e.g. due to backfill in conjunction with rock convergence or due to an increased internal pressure in the storage caverns) accompanied by positive effects, such as closing of pores and cracks, decrease of permeability and compacted deformation. Therefore the material damage and its healing are the basis for the description of the mechanical behaviour of rock salt. Both inverse processes must be taken into consideration simultaneously using a joint damage parameter.

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