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Untersuchungen an Tonschiefer im Hinblick auf dessen Eignung als Dammschüttmaterial

  • K. Schetelig
  • R. Sellner
  • F. Dannenberg
Conference paper

Summary

Previously, the mechanical properties of slate embankments as well as their permeability and susceptibility to erosion could only be reliably determined by large scale test fills. In order to obtain more precise predictions, petrographic investigations, ultra-sonic measurements and Los-Angeles-Tests were carried out on rock samples and their results were compared with measurements and experiences from existing dams.

Rocks up to a quartz content of about 75 percent appear as slates. All rocks of the series slate/quartz yield a very well graded granular fill and such rock fills are easily compacted (γd =21 - 23 kN/m3) in general. Sandstones, quartzites and solid slates in which mica and clay minerals enclose the quartz and feldspar grains in wave like manner, form favourable embankment materials with high shear resistance and rapidly occurring and small deformations. Furthermore, in such slates smooth and continuous cleavage planes do not exist. The quartz content alone is not a suitable parameter for the evaluation of the rock.

Severe disintegration of the rock and the tendency to long term Settlements are encountered with platy slates having cleavage planes intersecting the whole piece of rock and which consist of perfectly orientated phyllosilicates, and in cases where the proportion of swelling minerals is >5 percent, frequently combined with a haematite content > 3 – 5 percent (red slates).

Ultra-sonic measurements using P-waves beyond 45 kHz yield wave velocities in rock samples of 4 – 6.5 km/s. The anisotropy \( \frac{{{\text{V}}_{{\text{max}}} }}{{{\text{V}}_{{\text{min}}} }}\; = \;\frac{{{\text{v}}\quad {\text{s}}}}{{{\text{v}}\quad {\text{s}}}} \) was identified as a very important parameter.

Favourable embankment material yields an anisotropy of the wave velocity not more than 1.5. Higher values indicate distinct disintegration of the rock particles and longterm settelements resulting from this. Modified Los Angeles-Tests using 10 rock pieces each of about 1 kg and 100/500 cycles (drum rotations) are also very instructive. Rock materials yielding a content of fines (< 2 mm) exceeding 25 percent after the test, have a tendency to continuing deformations.

The permeability of slate embankments varies between 10–4 and 10–8 m/s, depending on the kind of rock. Due to the well-graded nature of slate fills, the susceptibility to piping is low, except for fills having a silt/fine sand content of 10 percent and consisting of mica.

Comparing the test results on slates with the investigations on the compaction, settlement and Saturation behaviour of granite fills (BRAUNS et al. 1980; KAST and BRAUNS 1981) it can be concluded that both rocks represent suitable embankment materials in general. Both kinds of rock yield a satisfying shear resistance and deformation behavior of the embankments provided sufficient compaction energy and an Optimum water content are applied during construction (BRETH 1972; SCHADE 1984).

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Literatur

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Copyright information

© Springer-Verlag Berlin Heidelberg 1985

Authors and Affiliations

  • K. Schetelig
    • 1
  • R. Sellner
    • 2
  • F. Dannenberg
    • 1
  1. 1.Geologisch-Paläontologisches InstitutTechnischen HochschuleDarmstadtGermany
  2. 2.ERdbaulaboratorium Dr. A.W. StreimFrankfurt/Main 61Germany

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