The aim of this article – to determine short term and long term strengthening of clay soil, by strengthening it with fly ash obtained during the production of mineral wool. This article introduces research which is used to determine the optimal ratio of fly ash in cement suspension for strengthening of clay soil. Samples which were investigated in this research work prepared by mixing Portland cement, mineral wool fly ash, clay powder, sand and water. All investigated samples compressive strength after 6 months exceeded 1.7 MPa. It is enough of such strength in geotechnics to conduct strengthening of soil and it is possible to argue that soil is strengthened.

Compressibility of quartz sand from the Lithuanian coastal area in Klaipėda environs is investigated by testing and numerical simulation, with validation of obtained results. The shape of sand grains has been analysed with a scanning electronic microscope (SEM). The determined morphological parameters of sand grains are employed to create discrete models (particle models of grains) subsequently used for sand compression test numerical simulation via discrete element method (DEM) techniques. The background version of DEM and the numerical time-integration algorithm are implemented in original DEMMAT code. Compression tests have been realised by an oedometer device. Test versus numerical simulation results have revealed a dependence of significant compression curve character on the discretised shape of sand grains and Young's modulus of particles.

The paper presents an application of statistical and numerical methods for the determination of the forcedisplacement curves and that of pullout capacity of prestressed grouted ground anchors installed in Miocene clay. A regression analysis of data from a database of acceptance test records for ground anchors to create has been performed, the force-displacement curve of the tested anchor corresponding to the range of loads applied for acceptance tests has been created. A linear regression model, employing the weighted least squares method and robust standard errors techniques were concluded to serve as a reliable statistical method suitable for achieving this goal. The discovered linear regression dependence then served as a lower control limit for the displacement values calculated at the anchor head applying the numerical model. A finite element model has been created to predict the behaviour of ground anchors being installed in fine-grained soils. The developed numerical model that employs Mohr-Coulomb strength criterion constitutive model evaluates the influence of high-pressure grouting by development additional radial stresses and that of an increment of fixed length diameter.

This work presents experimental tests on typical Baltic sea-shore sand along Klaipėda. The paper looks into changes in loaded soil void ratio when using different types of sand fractions in Klaipėda region. Three different types of sand fractions, including 1,18–0,6 mm, 0,6–0,425 mm and 0,425–0,3 mm were analyzed under laboratory conditions. In addition, one mixed sand fraction of diameter 1,18–0,3 mm was created from the equal parts (in mass) of these three different types of sand fractions. Soil usually consists of particles, water and air. An important basic parameter is void ratio e. The soil used under laboratory testing was air drained sand and water influence was not accounted. All tests on soil samples were recorded, because this is the only possible way of investigating the actual displacements versus time changes. Load increments were changed one minute later via the following loading steps: 0; 100; 200; 300; 400; 300; 200; 100; 0 kPa. Almost all displacements reached their final magnitudes in the first 5 seconds when load was increased; when unloaded, it took the first 3 seconds. When porosity is large, soil is called loosely packed. A laboratory test shows that maximum void ratio was in soil with 0,425–0,3 mm particle size where e = 0,840. The lowest maximum void ratio e = 0,714 was obtained for the mixed sand fraction and made 1,18–0,3 mm. The theoretical maximum soil void ratio can be e = 0,910, see Figure 3. This is the loosest packing of spherical particles that seems possible (minimum contact places between particle sizes are 4). Certainly, it is not stable: any small disturbance will make the assembly collapse. When using a very dense packing of spherical particles and the theoretical minimum soil void ratio of this assembly is e = 0,350, see Figure 4. This seems to be the major packing of a set of spherical particles (maximum contact places between particle sizes are 6). Minimum difference between the theoretical maximum void ratio and laboratory maximum void ratio was 0,07 in soil with particle sizes of 0,425–0,3 mm. Soil never consists of spherical particles and the values calculated above have no real meaning for actual soils. They may give a certain indication of what the void ratio of real soil may be. It can thus be expected that void ratio e may have a value somewhere in the range from 0,350 to 0,910. The results of the investigated sea-shore sand along Klaipėda confirms this statement. For Klaipėda sand, when loading it is better to show results of void ratio versus normal stress in lineral relationship (e = aσz + b), see Figure 10, and, when reloading to use semilogarithmic scale (e = alogσz + b), see Figure 11. In the general outline, one can make a conclusion that sand void ratio e decreases versus an increment in the size of soil fraction.

The article considers the peculiarities of determining quartz sand shear strength according to the Mohr-Coulomb strength criterion, via a direct shear test and that of factors influencing the characteristic angle of internal friction and cohesion values of the obtained strength parameters. The air-dry sand of the Baltic Sea region from Lithuanian coastal area near Klaipėda city has been analyzed. The solid density of the investigated sand grains was ρs = 2.65 g/cm3. The initial density of the tested samples made ~1.48–1.50 g/cm3. Processing data on the shear test yielded that the quantity of 18 tests was sufficient for the relevant accuracy of determining characteristic sand shear parameters of strength. This quantity of tests allow avoiding the influence of statistical coefficient tα that depends on a degree of freedom (K = n – 2). The paper presents additionally analyzed three different approaches to determining the characteristic shear parameters of strength and that of a comparative analysis of the applied approaches.