ABSTRACT

The paper presents investigation of carboniferous slates from the Trojane hilly area performed on series of samples of equal material. The results of static loading tests show that carboniferous slate is heterogeneous and yields on slate layers. Where that kind of heterogeneity is distinctive the strength results are essentially lower of commonly tests results. The results of dynamical loading tests show that the slate surfaces have the essential meaning for the stability of the material. When those surfaces are moistened the material become unstable.

RÉSUMÉ

L'article presente une epreuve des ardoises carbonifères de la region montagneuse de Trojane sur une serie des echantillons des materiaux identiques. Les resultats des tests de charge statique montrent que l'ardoise carbonifère est heterogène et qu'elle cède sur les couches d'ardoise. Quand l'heterogeneite est distinctive, les resultats de stabilite sont essentiellement plus bas que les resultats obtenus par des tests ordinaires. Les resultats des tests de charge cyclique montrent que les surfaces d'ardoise sont très importantes pour la stabilite du materiel. Quand ces surfaces sont mouilles, le materiel devient instabile.

ZUSAMMENFASSUNG

Der Artikel prasentiert die Forschung von Karbonschiefersteinen im Bereich des Bergland Trojane, ausgefuehrt durch Serien von Proben aus den gleichen Erdmaterial. Die Resultate der statischen Belastungspruefungen zeigen, das die Karbonschiefersteine heterogen sind und die Schieferflachen nachlassen. Wo bei dieser Art der Heterogenitat die Festigkeitsergebnisse wesentlich niedriger sind als bei gewöhnlichen Testergebnissen. Die Ergebnisse der zyklischen Belastungspruefungen zeigen das die Schieferflachen eine wesentliche Bedeutung fuer die Stabilitat des Erdmaterials haben. Wen diese Schieferflachen befeuchtet sind, wird das Erdmaterial unstabil.

Introduction

Carboniferous slates belong among soft rocks. In compact state, they can have rather good strength characteristics. Unfavourable mineralogical structure together with changed hydro geological and mechanical conditions can lead to the completely different (lower) strength characteristics of the slates, which are more similar to that of soils than rocks.

The paper presents the results of triaxial test of the aforementioned slates. For the purpose of laboratory strength tests, we received a larger number of perm-carboniferous slate samples from Trojane hilly area of the Ljubljana-Celje highway section. During erection it was namely demonstrated that the actual strength of slates, especially shear strength during the construction in slopes, is worse than it was proved by standard laboratory tests. Building contractors had a lot of problems due to instabilities of slopes.

Additional investigation of carboniferous slates was performed that include also the set of triaxial tests. Investigations were performed on series of samples of equal material. Tests were performed classically with incremental and continuous loading. Owing to schist structure of soft rock, tests were carried out in triaxial cells that allow placement of specimens up to 100 mm in diameter. The average largeness of specimens was 85 mm in diameter and 170 mm in height.

All tests were performed in natural moisture content after consolidation of specimens under a stress state similar to the in-situ state. Drained (vertically) and undrained tests were performed. Specimens were loaded with static and dynamic loading.

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