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Geotechnische Eigenschaften von überkonsolidierten Schiefertonen bei unterschiedlichen Sand- und Karbonatgehalten

  • Clemens Ruch
Conference paper

Summary

The rocks of the Middle Dogger in southwestern Germany provide excellent examples of several different kinds of weathering profiles. These rocks contain numerous natural drainage bodies such as jointed sandstone or calcareous sandstone complexes. These drainages can regulate both the depth and the number of weathering profiles (fig. 3). Vertical repetition of such natural drainage bodies throughout the section can create, in effect, multiple distinct zones of weathering.

The investigation of a large number of core drillings in the Middle Dogger demonstrates the existence of numerous horizontal plastic interlayers (ranging from mm to cm in thickness) which were formed as a result of horizontal stress releases and which occur mostly in zones of relatively low shear strength (fig. 4). These layers act as zones of latent weakness which can have significant mechanical effects on artificial slopes or deep excavations which may be constructed in these rocks.

Weathering tests simulating various climatic conditions have demonstrated that carbonate and sand components influence the weatherability of overconsolidated shales present in the Middle Dogger section (fig. 5). For example, a granular skeleton cemented with carbonate allows only a small amount of deformation. This deformation is the result of shrinkages caused by desiccation (tab. 2) and thereby initiate deconsolidation processes (EINSELE 1983). After undergoing three successive dry/wet deterioration tests, the primary, unweathered shales with a carbonate and sand content of more than 40 — 50% demonsträte only a small amount of slaking. However, if the carbonate and sand content exceeds 70%, the amount of slaking is too small to measure (fig. 5).

California Bearing Ratio (CBR) tests were also conducted with the Middle Dogger material. The results of these tests show bearing capacities which can be achieved when the investigation material is reapplied as embankment backfill. Unlike sandless shales or a mixture of Middle Dogger material consisting of 25% very sandy shale, 25% friable sandstone and 50% weathered sandless shale, the normally Consolidated, unweathered investigation material can be classified as “average” to “good” subsoil according to the CBR-norm (fig. 15). The low bearing capacity of sandless shale can be improved by adding friable sandstone material.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1985

Authors and Affiliations

  • Clemens Ruch
    • 1
  1. 1.Geologisches InstitutUniversität TübingenTübingenGermany

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