This paper presents the results of a laboratory study focused on evaluating the California Bearing Ratio (CBR) of various mixtures of fly ash and fine-grained soils, as well as mixtures of fly ash and slag. The fly ash used in the research was sampled from Serbian thermal power plants, and included both electrostatic precipitator ash (class F, non-self-cementing) and ash-slag blends from landfill. Two high-plasticity clays were investigated. Soil-fly ash mixtures were prepared at 15–20% fly ash content and compacted at the optimum moisture content determined from standard Proctor compaction tests. CBR tests were performed on all mixtures, as well as on pure fly ash, fly ash-slag blends, and selected stabilized mixtures with lime and cement activators. The results show a noticeable increase in CBR values for both soil types when mixed with fly ash, particularly for the expansive clay. Ash-slag mixtures also demonstrated favorable CBR values, comparable to natural subgrade materials. The application of activators further improved CBR values, indicating improved mechanical performance. These findings highlight the potential of using fly ash and fly ash-slag mixtures from Serbian power plants as sustainable alternatives to natural aggregates in subgrade stabilization and road and embankment construction.

During the construction of E75 highway through Grdelica gorge in Serbia, a major failure occurred in the zone of reinforced rock slope. Excavation was performed in highly anisotropic Paleozoic schist rock formation. The reinforcement consisted of the two rows of micropile wall with pre-stressed anchors. Forces in anchors were monitored with load cells while benchmarks were installed for superficial displacement measurements. The aim of the study is to investigate possible causes of instability considering different probability distributions of the strength of discontinuities and anchor bond strength by applying different optimization techniques for finding the critical failure surface. Even though the deterministic safety factor value is close to unity, the probability of failure is governed by variability of shear strength of anisotropic planes and optimization method used for locating the critical sliding surface. The Cuckoo search technique produces higher failure probabilities compared to the others. Depending on the assigned statistical distribution of input parameters, various performance functions of the factor of safety are obtained. The probability of failure is insensitive to the variation of bond strength. Different sampling techniques should yield similar results considering that the sufficient number of safety factor evaluations is chosen to achieve converged solution.

Nikola Obradović 1 Miloš Marjanović 2 Veljko Pujević 3 Mirjana Vukićević 4 UDK: 624.154(497.11) DOI: 10.14415/konferencijaGFS2021.16 Summary: Short review of provisions of Eurocode 7 for determination of pile axial bearing capacity is given in this paper. Design guidelines and recommendations for determination of bearing capacity of jacked-in MEGA piles, according to pile installation technology and chosen design approach in National Annex for Eurocode 7 (Part 1) in Serbia are presented. A validation of proposed guidelines through comparison with previous concept of allowable pile force is presented on the example of the rehabilitation of the foundations of a residential building in Zemun, Serbia. Obtained results confirm the adequacy of chosen design approach and proposed guidelines for determination of bearing capacity of MEGA piles.

Short review of provisions of Eurocode 7 for determination of pile axial bearing capacity is given in this paper.Design guidelines and recommendations for determination of bearing capacity of jacked-in MEGA piles, according to pile installation technology and chosen design approach in National Annex for Eurocode 7 (Part 1) in Serbia are presented.A validation of proposed guidelines through comparison with previous concept of allowable pile force is presented on the example of the rehabilitation of the foundations of a residential building in Zemun, Serbia.Obtained results confirm the adequacy of chosen design approach

Marine and harbor structures, wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures etc. can be subjected to significant lateral loads from various sources. Appropriate assessment of the foundations capacity of these structures is thus necessary, especially when these structures are supported by pile groups. The pile group interaction effects under lateral loading have been investigated intensively in past decades, and the most of the conducted studies have considered lateral loading that acts along one of the two orthogonal directions, parallel to the edge of pile group. However, because of the stochastic nature of its source, the horizontal loading on the pile group may have arbitrary direction. The number of studies dealing with the pile groups under arbitrary loading is very limited. The aim of this paper is to investigate the influence of the arbitrary lateral loading on the pile group response, in order to improve (extend) the current design approach for laterally loaded pile groups. Free head, flexible bored piles in sand were analyzed through the extensive numerical study. The main hypothesis of the research is that some critical pile group configurations, loading directions, and soil conditions exist, which can lead to the unsafe structural design. Critical pile positions inside the commonly used pile group configurations are identified with respect to loading directions. The influence of different soil conditions was discussed.

Special-purpose river port sediment was investigated for its potential use as a road construction material. Sediment samples were extracted from three locations in three small river ports, and detailed laboratory research was conducted to determine its basic mechanical properties and characteristics that can potentially have an adverse influence in a roadside environment. The results of the research conducted indicate that there is a need for systematic monitoring of the quality and quantity of sediment in special-purpose river ports of the Danube River Basin to maintain its mobility and prevent flooding. The basic engineering characteristics (Proctor elements, Atterberg limits, California bearing ratio, and unconfined compressive strength) determined represent the good potential of the sediment samples tested herein for use in road construction. In addition, the chemical characteristics tested indicate the need for detailed analyses of the potential environmental risk before application in civil engineering structures

Major infrastructure projects require significant amount of natural materials, often followed by the soft soil stabilization using hydraulic binders. This paper presents the results of a laboratory study of alternative waste materials (fly ash and slag) that can be used for earthworks. Results of high plasticity clay stabilization using fly ash from Serbian power plants are presented in the first part. In the second part of the paper, engineering properties of ash and ash-slag mixtures are discussed with the emphasis on the application in road subgrade and embankment construction. Physical and mechanical properties were determined via following laboratory tests: Specific gravity, grain size distribution, the moisture-density relationship (Proctor compaction test), unconfined compressive strength (UCS), oedometer and swell tests, direct shear and the California bearing ratio (CBR). The results indicate the positive effects of the clay stabilization using fly ash, in terms of increasing strength and stiffness and reducing expansivity. Fly ashes and ash-slag mixtures have also comparable mechanical properties with sands, which in combination with multiple other benefits (lower energy consumption and CO2 emission, saving of natural materials and smaller waste landfill areas), make them suitable fill materials for embankments, especially considering the necessity for sustainable development.

In this paper, the assessment of the sensitivity of the soil in the rural area of Čukarica municipality to the processes of degradation is considered. Land areas, especially in the vicinity of large cities, are exposed to numerous processes of degradation: soil erosion, urban and industrial zone expansion at the expense of fertile agricultural soils, activation of landslides and a number of other significant ecological problems. Based on the characteristics of the research area, the MEDALUS (Mediterranean Desertification and Land Use) model was applied, and for the assessment of sensitivity to the processes of degradation the main quality indicators were considered: soil, climate, vegetation and management. For each of the analyzed quality indicators, parameter groups were identified. Each parameter is quantified according to the defined method by giving them a sensitivity coefficient between 1.0 and 2.0. ArcGIS 10.0 has been applied to analyze and prepare layers of quality maps. Subsequently, the geometric mean for all four quality indicators was used to generate the map of environmental sensitivity to degradation. The results obtained show that 41.54% of the study area is classified as critical; 22.34% of the surface as fragile; 8.47% of the areas are potentially endangered and 9.58% not threatened to degradation processes. The results have also shown that MEDALUS model is a functional tool for simulations which support sustainable land management in the areas prone to degradation.

This paper presents the results of laboratory research of physical and mechanical properties of fly ash and mixtures of fly ash and slag from landfills of thermal power plants "Nikola Tesla" and "Kostolac" in terms of their use for road embankments construction. Following mechanical material properties were tested: unified compressive strength (UCS), shear strength, deformability, CBR, and resistance to frost. Results of the study have shown that waste materials from Serbian thermal power plants can be successfully used as the building and reconstruction material for road subgrade. This can bring multiple economic benefits, such as: saving of natural materials, lower energy consumption, lower pollution of environment, and less waste landfill areas.

This paper presents the evaluation of methods for predicting the ultimate axial bearing capacity of single piles based on the cone penetration test (CPT) results, and the evaluation of static methods based on the effective and total stress analysis. Seventeen jacked-in MEGA piles and eight Franki piles of different lengths are considered. The results show that the Bustamante & Gianeselli (LCPC) method is the most appropriate for the studied geotechnical conditions and pile types.

The ash landfills are a major environmental issue. The use of ash for the highway and railway substructure achieves a double benefit: it significantly reduces the deposited quantities of ash as well as the consumption of natural materials such as crushed stone, gravel and sand. The investigation of engineering properties of fly ash from the power plant in Serbia was conducted at the Laboratory of Soil Mechanics at the Faculty of Civil Engineering in Belgrade. Relevant physical and mechanical properties of ash and mixtures with binders (cement/lime) were investigated. The ash was also tested from the aspect of the potential environmental impact, which primarily depends on the leaching behaviour of the present trace elements. The results of the study showed that fly ash meets technical and environmental requirements and that has the potential for use in highway substructure, such as construction of embankments and stabilization of soft soils. Benefits of utilization of ash and slag was shown in the case of the construction of a high embankment on soft soil on the highway section Obrenovac-Ub in Serbia.

The results of laboratory research of high plasticity clay stabilization using liquid chemical additive Polybond and the fly ash from Serbian thermal electric power plant Kostolac are presented in this paper. In order to determine the effects of stabilization, extensive laboratory study of physical and mechanical properties of the stabilized soil (unconfined compression strength, shear strength parameters, CBR, deformation parameters, swelling, coefficient of permeability, resistance to freezing) were performed. The results of the research clearly indicate the positive effects of the clay stabilization using Polybond, as well as fly ash, and confirm that these additives can be successfully applied as a clayey soil stabilizers in various practical applications such as: stabilization of low bearing subgrade, construction of embankments and geotechnical structures of low permeability, improvement of mechanical properties of top subgrade layers etc. The use of stabilizers reduces energy consumption, as well as the usage of natural materials such as stone aggregates.

Realistic modeling of pile groups requires the use of complex nonlinear 3D simulations, usually with full discretization of pile continuum.In order to reduce the complexity of these models, as well as the computation time, in past years an embedded beam element has been formulated and implemented into FEM computer codes such as PLAXIS 3D.This concept was originally intended for modeling axially loaded piles and pile groups, while its performances under lateral loading conditions are not fully investigated.This paper presents the overview of different modeling techniques of laterally loaded pile groups using FEM.The possibility of using embedded beam model for this problem, as well as its limitations, have been discussed.

Miloš Marjanović 1 Mirjana Vukićević 2 Diethard König 3 Tom Schanz 4 René Schäfer 5 UDK: 624.154.042 DOI:10.14415/konferencijaGFS 2016.035 Summary: Realistic modeling of pile groups requires the use of complex nonlinear 3D simulations, usually with full discretization of pile continuum. In order to reduce the complexity of these models, as well as the computation time, in past years an embedded beam element has been formulated and implemented into FEM computer codes such as PLAXIS 3D. This concept was originally intended for modeling axially loaded piles and pile groups, while its performances under lateral loading conditions are not fully investigated. This paper presents the overview of different modeling techniques of laterally loaded pile groups using FEM. The possibility of using embedded beam model for this problem, as well as its limitations, have been discussed.

СТАБИЛИЗАЦИЈА ВИСОКО ПЛАСТИЧНЕ ГЛИНЕ ПРИМЕНОМ

Results of laboratory research focusing on soil stabilization, using fly ash without activators, are presented in the paper. Two types of fine-grained soils were tested: low to medium plasticity clay and very expansive, medium to high plasticity clay. Soil-fly ash mixtures were prepared at optimum fly ash contents (15 and 20%). The effects of fly ash on the soil plasticity, moisture-density relationship, unconfined compressive strength, shear strength parameters, CBR (California Bearing Ratio) values, deformation parameters, and swell potential, were evaluated. Results obtained show that the use uf fly ash can significantly contribute to the improvement of soil properties.