Presented herein is a comparison of the results of laboratory model tests used to study the bearing capacity of geogrid and geotextile reinforced earth slabs. The parameters studied were the coefficient of friction between the geotextile and the soil, pull-out resistance between the geogrid and the soil, depth below the footing of the first layer of reinforcement, vertical spacing of the layers, number of layers, width size of a square sheet of reinforcement, and tensile strength of the reinforcement. For both geogrids and geotextiles, after an optimum number of layers or width of reinforcement, the bearing capacity did not increase. In addition, the bearing capacity was largest for those geogrid and geotextile reinforced earth slabs where the first layer was closest to the footing and the spacing between the layers was the smallest. Bearing capacity increased directly with increasing reinforcement tensile strength for the geotextile; however, for the geogrid, aperture size and reinforcement tensile strength must be looked at simultaneously. Key words: reinforced earth slab, geogrid, geotextile, bearing capacity, pull-out, friction.

The Kupferschiefer, a thin (<4 m) bed of marine bituminous marl of Upper Permian (Zechstein) age, occurs over a large area of north-central Europe and has, in certain areas, been exploited for silver and some base metals, notably copper, since medieval times. It has been regarded as the type example of a shale-hosted, strata-bound sulfide deposit and theories regarding the origins of Kupferschiefer mineralization have exerted considerable influence on theories of ore genesis. The Kupferschiefer sediments were deposited following a rapid marine transgression over an area that had been subject to a very long period of arid to semi-arid conditions. In many areas the Kupferschiefer overlies red-bed sediments (Rotliegende), but in others it overlies Carboniferous sandstones and marls or the bleached and reworked equivalents of earlier rocks (Grauliegende and Weissliegende). Within the Kupferschiefer, lithologieal variations can be related to detailed paleogeography. Overall a euxinie, sapropelie facies predominates, but changes occur in the region of paleohighs where more carbonate and elastic-rich facies are developed. Strong evidence exists for the development of chemical stratification in the Zeehstein sea (from which the Kupfersehiefer was deposited) with oxidizing conditions in the upper part and reducing conditions in the lower part. Everywhere the Kupferschiefer grades upward into overlying dolomitie limestones. Although large areas of the Kupfersehiefer contain only average concentrations of base and precious metals compared to other shales and marls, in certain areas the concentrations reach ore grade. Historically, the Mansfeld district (SE Harz Mountains) was important for copper and silver mining, but at present-day mining is undertaken only in the Spremberg-Weisswasser area (East Germany) and in Lower Silesia (Poland). The ores in such regions contain sulfides of Cu, Pb, and Zn and may be enriched in a variety of other elements, notably V, Mo, U, Ag, As, Sb, Bi, and Se; Cd, T1, Au, Re, and the platinum-group metals are also reported; lateral and vertical zoning of Cu, Pb, and Zn may be observed; and in some areas, a reddening of the rocks adjacent to ores (Rote Fiiule facies) is a useful exploration guide. The Kupfersehiefer in Poland, in two contrasting regions in Germany (the Lower Rhine basin and the Hessian depression) and in England (where it is termed the Marl Slate) are compared and provide evidence for four types of mineralization. The first (and oldest) is a weakly mineralized type exemplified by the English Marl Slate. Average base metal content of this type is • 100 ppm. Detailed mineralogieal, geochemical, and isotopic studies indicate that the mineralization is synsedimentary; these studies have enabled a model to be developed in which precipitation of the various mineral phases can be related to stratification of the early Zeehstein sea and oscillations in water and oxie-anoxie boundary levels. The second is an average mineralization involving base metal content at the 2,000-ppm level. In th...

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