Zustandsbeschreibung und Verwitterbarkeit des eozänen Messeler Ölschiefers

Summary

In the abandoned oil shale pit “Grube Messel” fossils are excavated and rubbish ought to be deposited (fig. 1). The diggers and the deposition are threatened by slope failures. In order to investigate the slope stability the soil physical parameters of primary indisturbed core samples were determined (table 1 and 4).

The material can be divided into a bituminous clay/silt mixture. The elutriation analyses or the combined sieve- and elutriation analyses proved that all layers have a fluctuate portion of clay between 57 – 8% (fig. 2). The water absorption of a desiccated sample is very slow; at first after 24 h 0,4 were obtained and after a month 0,74 (fig. 4). By reiterated desiccation and moistening the water absorption increased, after ten repeated interactions a water content of up to 0,50 was obtained. In vacuum the absorption capacity increases faster and stronger 0, 61 (fig. 5). In spite of a high content of active clay minerals the water content will not increase after ten repeated remoistening phases because the montmorillonites will be masked by kerogenes. The falling into pieces prevails.

The laboratory tests for weathering of the material were accomplished in six series as pointed out (fig. 6):

• 1) already after one desiccation an evident Separation of beds is distinguishable,

• 2) the influence of frost action is of less importance, it increased under vacuum conditions,

• 3) the series of investigation “desiccation-moistening” is the decisive criterion for desintegration,

• 4) the series of investigation “A — B in vacuum” (at 3 0 mbar residual pressure) lead to a comparable stronger comminution.

The uniaxial shear test yielded strongly deviating values for the angle of internal friction in relation to bedding and shear planes. In the case of steeper inclined layers the angle of internal friction obtained an angle of 46° and in the case of horizontal bedding an angle of 26°. That is important because the layers have a steep inclination. The compression tests in the case of horizontal layers at 80 N/cm2 obtained a final settlement of 0,39 mm (tab. 3). The pressure of overlying strata (here max. 150 m) is of no distinguishable influence on the geological preloading and on all the soil physical parameters.