Volume 29 (2021): Issue 2 (June 2021)

The improvement, reconstruction and repair of roads in recent years have increased the content of recycled asphalt in pavements. Using these materials in road construction projects because they reduce the costs, will also be of great help in improving environmental issues. In the present study, dune sand, which can be found in most desert area soil but does not have proper strength and loading capacity for a subgrade, was used. In order to increase the strength parameters of dune sand, various contents of cement and recycled asphalt were examined in California Bearing Ratio (CBR) and compressive strength tests. The results showed that the addition of cement and recycled asphalt can increase compressive strength and bearing capacity and reduce rupture deformations. In a stabilized sample with 27.5% recycled asphalt, increasing the cement from 7.5 to 12.5% increased the compressive strength by 1.045 times, which is the highest amount of change in the samples studied. The maximum CBR and minimum rupture deformations are related to 35% of the recycled asphalt and 12.5% of the cement. The predicted functions of the compressive strength, deformation and CBR depend on two variables of the cement content; the recycled asphalt was then calculated using the response surface method

The importance of water reservoirs in the uneven distribution of discharges over time and space does not need to be explicitly justified. There is a more than 6,000-year history of convincing evidence. In Slovakia, the construction of reservoirs can be dated to two periods. The first period was the 18th century, when the construction of water reservoirs was stimulated by the need for water for the mining industry in the vicinity of the town of Bánska Štiavnica. The second period falls into the second half of the 20th century. The construction of reservoirs was initiated by the post-war period, including the need to increase society’s standard of living, the electrification of the region, the development of industry and agriculture, flood protection, etc. Reservoirs with multi-annual regulations have an essential position in the types of water reservoirs. While small water reservoirs and annual or seasonal regulation can regulate flows in a short period, reservoirs with multi-annual regulation can regulate flows over several years. This benefit is evident, especially during periods of extreme hydrological phenomena and short-term aquatic and long-term dry, so-called low water periods. We have illustrated our knowledge of and experience gained from their impact on the flows downstream of the Veľká Domaša dam. We analyzed two time periods, i.e., before and after the year 2000. The influence of extreme hydrological phenomena on the runoff conditions downstream of the dam is presented by statistical processing of the available flow series

An analysis of combined piled raft foundations could be performed by means of a special geotechnical finite element software that utilizes 3D modeling and advanced constitutive models for the soil. However, a foundation is generally included in the structural models in a structural design program. The least advanced part of finite element software that has been developed for structural FEM modeling are the tools used for modeling behaviour. A method is required with which the input parameters of the structural design software that are used for modeling the soil structure interaction as well could be determined so that the results calculated by means of a geo-technical software that approximates realistic soil behaviour the best can be reproduced by structural design software as well. The procedure outlined in this paper by means of a cluster analysis provides a tool for a substantial and innovative improvement in subsoil modeling, to which not enough attention is generally paid in the structural FEM software, thereby resulting in a reduced amount of work associated with the task of inputting data.

The extensive use of commercial activated carbon as an adsorbent for the purification of industrial effluent is not economical for small and medium-sized enterprises due to its high operational cost. This study was carried out to compare the adsorptive capacity of bentonite clay and activated corn cob (“BC” and “ACC”) for the removal of lead (II) and nickel (II) ions from an aqueous solution. The results obtained from the characterization of the BC and ACC are pH: 7.43 and 6.74; moisture content: 36.45kg/kg and 12.10kg/kg, and bulk density: 1.243g/ml and 1.162g/ml, respectively. Normality tests using the coefficient of skewness indicated that the set of data was not normally distributed. An analysis of variance (ANOVA) test conducted using Friedman’s 2-way ANOVA test indicated p values of 0.0253 against an alpha value of 0.05, which indicates significance. The Friedman results indicated significance with respect to the varied dosages, initial concentrations, and contact time. The effect of the adsorbent was not significant. The adsorption isotherms were analysed using the Langmuir, Freundlich, and Temkin isotherms. Most research studies have shown that adsorption experiments performed using most low-cost materials tend to follow the Freundlich adsorption isotherm, but the results of this experimental study proved that activated corn cob and bentonite clay performed better with the Temkin adsorption isotherm with 0.879 ≤ R² ≤ 0.917 for the bentonite clay and 0.9572 ≤ R² ≤ 0.99 for the activated corn cob respectively. The study revealed that these materials are good adsorbents that can be used for the removal of lead (II) and nickel (II) ions from an aqueous solution.

In this study, a depth-averaged numerical model was employed to investigate the two-dimensional flow features of transitional open-channel flows from a supercritical to a subcritical state. Compared to a shallow-water model, the proposed model incorporates supplementary terms to account for the effects of non-uniform velocity and non-hydrostatic pressure distributions. The model equation was solved numerically by means of the Adams–Bashforth–Moulton scheme. A wide variety of transitional open-channel flow problems such as hydraulic jumps was considered for assessing the suitability of the numerical model. The results of the model for the free-surface profile, pressure distribution, and characteristics of the first wave of an undular jump were compared with the experimental data, and the agreement was found to be satisfactory. Despite the effects of the three-dimensional characteristics of the flow and the bulking of the flow caused by air entrainment, the model performed reasonably well with respect to the simulations of the mean flow characteristics of the curvilinear turbulent flow problems. Furthermore, the results of this investigation confirmed that the model is more suitable for analyzing near-critical turbulent flow problems without cross-channel shock waves.

The reinforcement of soil is used to improve its strength and stiffness. The standard method of soil reinforcement is an application of geosynthetics. Soil reinforcement by distributed discrete fibres represents an alternative to those techniques. Currently used fibres have a straight shape, uniform cross-section, and smooth surface, which is not optimal in terms of the fibre-soil interaction. In this study, fibres with a variable shape were utilized. The fibres were fabricated using a fused deposition modelling technology. Firstly, a brief theoretical background is presented. Then, the proposed shapes of the fibres and their manufacturing process are described. The mechanical properties of the soil-fibre composite were investigated through consolidated drained triaxial tests. Well-graded coarse sand and poorly-graded fine sand were used. A higher peak shear strength was observed in the case of fibres with a variable shape. The effect of the variable shape of the fibres on the peak shear strength was higher in the case of the coarse sand.

Our calculation of wind effects was based on the specific wind situation of the planned R2 expressway. Given the topography and the prevailing wind directions, it was necessary to analyse the speeds for winds that could cause vehicles with trailers to be pushed off the roadway, as has been observed in recent years. Using a CFD simulation in the ANSYS FLUENT program, we analysed the entire section of the planned R2 expressway in order to evaluate the wind speeds at the level of the centre of gravity of truck trailers. Statistical turbulence models based on a time-averaging method, i.e., the RANS-Reynolds Averaged Navier-Stokes equations, of turbulent flow quantities and the time-averaging procedure of balance equations are suitable for solving the engineering tasks. In numerical simulations, the Realizable k - ε model was used in which the calculation of the turbulent dynamic viscosity in the equation for Boussinesque’s hypothesis was solved using two transport equations. Plotting and comparing the wind speeds for significant wind directions allowed us to design protection in the dangerous areas using protective walls.