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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 α, 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 α 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 α 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.

The article deals with a deformation analysis of a road embankment under different types of static and cyclic loading. A typical cross-section of a road embankment supported by geogrid retaining structures is considered. In the case of a design, the load is usually applied as a distributed static load. The analysis presented in the paper includes all the most loading methods used. Because there are only a few measurements for these types of construction in a given region, the analysis also includes a cyclic loading that aims to simulate real traffic loading. The cyclic loading considered the weights of cars and trucks and the distances between them, based on traffic intensity measurements. The study results showed how significant the differences in vertical and horizontal deformations of an embankment are when the different types and methods of static loading are used in a design. The results of the cyclic loading showed the deformations that can be expected from current real traffic.

The paper deals with an analysis of the shear strength behaviour of coarse-grained materials using large-sized direct shear apparatus. The shear strength curve of compacted coarse-grained material allows for determining the three typical shear strengths, i.e. the shear strength for a maximum density of the sample tested (shear strength at point A), the peak shear strength (shear strength at point P), and the critical shear strength achieved for a large horizontal movement (shear strength at point C). Professional laboratories usually apply for determining the critical shear strength two different methods. The first method considers the critical shear strength at point A and the second method considers the critical shear strength at point C. The aim of the article is not to critically evaluate both methods, but to analyze the results of shear tests of gravels. The results of a large series of tests showed that these stresses may differ from each other in some cases, especially for poorly graded materials. In the case of sandy soil, the shear strength at point A and at point C is equal. However, in the case of poorly graded gravel, the shear strength at point C is greater than the shear strength at point A. The greatest difference between these shear strengths was measured in the case of poorly graded medium gravels. The results showed that the ratio of shear strength at point C to the shear strength at point A increases with increasing the grain size of the material tested. The peak as well as the critical shear strength parameters of poorly graded gravels is better represented by a multi-linear or a nonlinear failure line.

The article deals with designing and analysing a wrapped geogrid reinforced structure (GRS) with a passive facing system. The analysis has been done using analytical calculation and numerical modelling. The analytical calculations were executed using FINE Geo5 geotechnical software, and numerical modelling was executed using Plaxis 2D software. The analysis is focused mainly on comparing tension forces in geogrids and the stability of the reinforced embankment determined using both computational methods. The deformation analysis was done only using numerical modelling. The numerical modelling allowed for a more detailed analysis of the wrapped GRS. Each construction phase was modelled step by step according to an actual construction procedure. Two complex road embankments supported by GRS were modelled and analysed. The first model consisted of three GRS, which not affected each other. In the second model, the GRS at each side of the embankment influenced each other. The analysis results showed that tension forces in geogrids, determined using both computational methods, can differ significantly from each other. The stability of the reinforced embankment determined using numerical modelling was within the range of 0.87 – 1.22 of the stability determined using analytical calculation. The numerical modelling results showed that the final horizontal deformation of the passive facing is about 2.8 – 3.8 times smaller than the deformation of the wrapped GRS, which occurs during the construction of the embankment.

The peak shear strength of dense coarse-grained soils is defined by the angle of the shear strength, the initial shear strength, and the angle of dilatancy. This paper mainly focuses on determining the angle of dilatancy. This parameter has been investigated by many researchers on sands or sand-gravel mixtures. The study aims to determine the dilatancy angle of various types of gravel soils using a large-size direct shear test. The results demonstrated that the dilatancy angle decreases with an increase in the normal stress. The gravels tested were separated into 8 groups based on the type of gravel, the fraction, and the shape of the grains. The relation between the dilatancy angle and the normal stress was correlated using a power function for each gravel group. The results also showed that simplified assumptions of the dilatancy angle, which are usually applied in the design of geotechnical structures, can lead to a determination of a higher value of the dilatancy angle than that determined by laboratory measurement. A simple correlation is presented, which allows for determining the angle of dilatancy from the peak and the critical angle of the shear strength in a given normal stress range. [ABSTRACT FROM AUTHOR]

Designing the improvement of soil using stone columns is usually based on simplified analytical or numerical models. Stone columns installed using a vibro-replacement technique can cause radial displacement of the original soil. It can cause radial compaction of the soil and increase the values of the strength and deformation properties, which are usually ignored in a practical design. The paper presents the results of a numerical analysis of a road embankment based on subsoil improved using stone columns. The changes in the properties of the original subsoil compacted by stone columns were analysed and taken into consideration in the models. The results showed that a model with homogenization of the subsoil and a model with stone columns transferred to continuous walls show similar results of the final settlement as well as the consolidation times. The differences between the values computed and measured were about 28 - 36 %. Taking into account the compacting effect of the original subsoil, the model with stone columns transferred to continuous walls allowed for the determination of more precise results when the difference between the values computed and measured was about 10 %.