The paper deals with the laboratory testing of coarse-grained soils that are reinforced using a geogrid. The shear strength properties were determined using a large-scale direct shear test apparatus. The tests were executed on original as well as on reinforced soil, when the geogrid was placed on a sliding surface, which permitted determining the shear strength properties of the soil-geogrid interface. The aim of the tests was to determine the interface shear strength coefficient α, which represents the ratio of the shear strength of the soil-geogrid interface to the unreinforced soil. The tests were executed on 3 samples of coarse-grained materials, i.e., poorly graded sand, poorly graded fine gravel and poorly graded medium gravel. Two types of geogrids were tested, i.e., a woven polyester geogrid and a stiff polypropylene geogrid. The results of the laboratory tests on the medium gravel showed that the reduction coefficient α reached higher values in the case of the stiff polypropylene geogrid. In the cases of the fine gravel and sand, the values of the interface coefficient α were similar to each other. The shear strength of the interface was reduced or was similar to the shear strength of unreinforced soil in a peak shear stress state, but significantly increased with horizontal deformations, especially for the fine gravel and sand. The largest value of the coefficient α was measured in the critical shear stress state. Based on the results of the testing, a correlation which allows for determining the optimal grain size distribution was obtained.

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Abstract. The paper presents specific example of method of intensification of ash impoundment. The impoundment for permanent bedding of ashes is situated on the left side of the Danube river. Part of the dam system of impoundment is based upon the original flood bank of Danube river. At the selection of materials for elevation of the impoundment, the decision was made primarily according to two indicators with an economic aspect -the transportation distance and the increase of the accumulation volume of the impoundment. Finally, the decisive criterion was the occurrence of the failure rate of the ash dam systems in comparison with the dams built from loess soils. As the impoundment is situated in the immediate vicinity of the Danube river, safe and failure-free operation has the priority. There is compared the geotechnical characteristics of the loess soils in the original deposition and the loess soils compacted at optimum water content by Proctor Standard compaction test. The proposed method of intensification of ash impoundment is analyzed. The stability analysis provides an example of the utilization of the results of the monitoring of the geotechnical properties of the materials forming the impoundment´s body and the surrounding rock mass. IntroductionThe impoundment for permanent bedding of ashes from the power-producing operations is situated on the left side of the Danube river in the municipality of Štúrovo. The impoundment is partially flown through by surface waters, it is planar, with a circulation system of transport water, with dams on its southern, western and eastern sides. From the north, the impoundment is bounded by a natural slope. The relative position of the impoundment and Danube river is presented in Figure 1 (Google Earth).The original surface of the terrain was at the ground elevation of 104.8 m above the sea level. The dam system of the impoundment consists of the basic dam with its crest at the elevation of 109.2 m altitude and of elevation dams with crests at elevations of 113.5 m and 116.2 m above the sea level, elevated by a method against water and built from local soils, with inclination of downstream slopes of 1:2.5. The lateral section across the dam system of the impoundment is presented in Figure 2. At the southern side, the dam system of the elevation dams is based upon the original flood bank of Danube. In the direction north -south it is divided by a dam into two cassettes. Deposition into the cassette No.1 was finished in the year 1983 at elevation of 120.0 m above the sea level and at present, only the cassette No. 2 is operated occasionally.

This paper analyzes the transformation of the culvert channel under the supply channel of the Gabcíkovo Waterworks into a road tunnel structure and the impact this had on the surrounding rock environment. It presents the engineering-geological conditions in the area, the current structuralmaterial characteristics of the culvert channel and its proposed transformation into a road tunnel. The results of the geotechnical analysis, realized through numeric modelling, are presented as a comparison of deformation changes in the rock environment with respect to changes in loading states corresponding with functional changes in the analyzed culvert.

The paper presents the results of the shear strength measurements of a soil-geosynthetic interface. The tests were executed using a large-size direct shear test apparatus. A total of 5 different samples of materials were tested, i.e., ash, sand, well-graded gravel, fine poorly-graded gravel, and medium poorly-graded gravel. These materials were reinforced using different types of geosynthetics, i.e., Thrace WG80 black woven geotextile, Tencate Miragrid GX55/30 woven geogrid, and Thrace TG3030S rigid polypropylene geogrid. An interface coefficient a, which represents the ratio of the soil-geosynthetic interface shear strength to the shear strength of unreinforced material sample, was determined for given combination of the material and geosynthetics. The coefficient a reached a greater value in the critical stress state than in the peak stress state for sands and gravels reinforced using GX55/30 and TG3030S geogrids. The value of the coefficient a was in a range of 0.87 - 1.04 for gravels and 1.03 - 1.19 for sand. The black woven geotextile was used as the reinforcement only in samples of sand and ash. The results pointed to the different behaviour of these materials in the testing of the interface shear strength.