Rock masses are inhomogeneous, fractured, anisotropic, and initially stressed in their natural state. They consist of intact rock or rock monolith and macro-damages, which include fractures, bedding planes, faults and other forms of discontinuity. It has been experimentally confirmed that with the increase of the rock mass scale, the mechanical properties of the rock mass decrease as a consequence of discontinuities. The subject of this paper is the analysis and determination of the scale effect on the damage plasticity model parameters, which describe the mechanical behaviour of the rock mass for different loads and scales. The scale effect is analysed on a constitutive model that can simulate the most complex mechanical behaviours in rock masses (elasto-plastic with damage in stiffness and strength). The analysis is based on the results of experimental tests of rock mass, which were carried out for different scales (scale of the rock mass sample in laboratory and scale of the in situ test - shear test), while the tests were performed at the same microlocation. For the considered experimental tests, appropriate finite element models (FEMs) were formed with boundary conditions that correspond to the ones from the experiments. By simulating the performed experiments with a series of FEM analyses with complex optimization algorithms, the parameters of damage plasticity model were determined for both values of the rock mass scale, proving the scale effect numerically. Based on the obtained results, analysis and discussion of the scale effect for a given rock mass were performed.

In the scope of Phase I of Line 1 of the Belgrade Metro project, a large laboratory and in-situ testing database of the soils and rock masses of Belgrade was used for determining the parameters of the hardening soil model with small strain stiffness (HSS). Due to the complexity of parameter determination of the HSS model based on conventional laboratory testing results, an optimization approach coupling finite element analyses and genetic algorithms was taken in the parameter determination process with the goal of defining a framework for full, reliable, and unified implementation of the HSS model in all necessary numerical analyses. For the selected geotechnical soil layer, each of the available laboratory tests (direct shear test and CD triaxial test) and in-situ tests (pressuremeter) were numerically simulated and the HSS parameters were calibrated so that each individual simulated test, consisting of multiple test specimens, could achieve its respective experimental recordings as best as possible by minimizing the value of the applied criterion function. The resulting parameters from the calibration process, alongside the analytically derived parameters for laboratory results, were compared and analyzed, and it is realized that while analytically derived parameters provide a reasonable first estimate, numerical calibration is essential for accurately capturing soil stiffness behavior and stress dependency and therefore creating reliable design solutions based on realistic soil properties.

The paper presents various examples of the application of the PAK software and its modules for thermal, filtration, and stress-strain analysis of different complex engineering structures such as and projects in which PAK has been applied to assess the condition of various structures are provided. Special emphasis is placed on the application of PAK for modeling thermal, filtration, and stress-strain processes at the gravity dam, Iron Gate I Dam, and the arch dam, Gran & ccaron;arevo. PAK has been successfully used for a long time on these structures as part of the Dam Safety Management System, providing the basis for various analyses and reports on the assessment of dam condition and safety.

Precise control of face pressure is essential in shield TBM tunneling to limit surface settlements and ensure the stability of surrounding structures, particularly in densely built-up urban environments. This study focuses on determining the optimal shield TBM face pressure for the specific geotechnical conditions of Phase 1, Line 1 of the Belgrade Metro, along the section from Bele Vode Station to Trgovačka Station. Three-dimensional numerical models, developed using a staged construction approach, realistically simulate sequential excavation, shield advancement, and segment installation, while incorporating representative ground properties and structural characteristics. A sensitivity analysis is conducted by systematically varying face pressure values to assess their influence on the magnitude and distribution of surface settlements. The results identify an optimal face pressure range that minimizes surface settlements while maintaining excavation stability. These findings provide practical guidance for shield TBM operation in urban tunneling, contributing to more effective settlement control and improved risk mitigation in shallow urban tunnel construction.

Tunnelling in urban conditions is often met with demanding criteria for surface settlement control, the limitation which is arising from the fact that most of the urban area is occupied by structures which are sensitive to deformations, such as buildings, roads, communal infrastructure etc. Another important necessity in any project is to deliver the project in shortest amount of time possible. Temporary occupation of public areas for construction sites and traffic congestions alleviate social pressure which further emphasizes these requirements. If planned correctly, TBM technology promises to deliver on these requirements more readily than conventional tunnelling techniques. In this paper a Case study of Belgrade's double tube traffic tunnels is presented, in which project design went through significant conceptual transition, led by the designer's idea to change the technology of excavation from conventional to TBM, as well as to adjust the project in multiple ways to accommodate for this major turn of tides. Most notable historic background of the project is presented. Geotechnical profile of tunnels and data are shown and calculations for both TBM and conventional variants are presented and discussed.

Monitoring data provide valuable information on embankment dam behavior but are typically not integrated into a classical probabilistic safety assessment. This paper introduces a Bayesian-inspired methodology to directly integrate actual dam monitoring records into a Monte Carlo probabilistic safety assessment using a finite element framework, without recalibrating the original input parameters ‘distributions. After the baseline (unweighted) set of simulations is generated, the method assigns a weight coefficient to each simulation outcome based on the likelihood of matching monitoring data, effectively updating the baseline probabilistic analysis results. Therefore, such “weighted” analysis produces an updated probability distribution of the dam’s factor of safety (FS) that reflects both prior uncertainty of model parameters and actual monitoring data. To illustrate the approach, a case study of a rockfill triaxial test specimen is analyzed: a baseline probabilistic analysis yields a mean FS ~1.7, whereas the weighted analysis incorporating monitoring data reduces the mean FS to ~1.5 and narrows the variability. The weighted analysis suggests less favorable conditions than the baseline projections. This methodology offers a transparent, computationally tractable route for embedding monitoring evidence into reliability calculations, producing more reflective safety estimates of actual dam behavior.

In this paper, we focused on the advancement of Dam Monitoring Software that incorporates the Finite Element Method (FEM), as these large infrastructure constructions are crucial for ensuring a dependable water supply, irrigation, flood control, renewable electric energy generation, and safe operation, which is of utmost importance to any country. However, the material properties and geotechnical environments of dams can change (deteriorate) over time, while the standards and legal norms that govern them become more and more rigorous, so in order to accurately assess the state of a dam and detect any concerning behavior, the software must be updated as well. The custom-developed FEM solver, unlike many commercial alternatives, is adaptable and can be reconfigured to function within a Dam Monitoring System. In this paper, we present the procedure for interpolating numerical values at measurement points, when the position of the measurement point does not align with the node of the element, allowing for additional instrument locations to be added to the monitored system without the need for remeshing the numerical model. This procedure is used to compare the actual pore pressures and temperature values of the concrete dam structure with the prediction of the numerical model, and the agreement is much greater with the new interpolation algorithm in comparison to the nearest nodal values, with the average relative difference for pore pressure reduced from 8.89% to 8.10%, justifying this implementation.

The paper presents the procedure for determining the factor of safety (FoS) using the strength reduction method (SRM) for the case of a concrete damage plasticity constitutive model. The SRM was originally used in a slope stability analysis and in its original form, this method was applied by reducing the shear strength of the material. Since damage in concrete occurs due to exceeding the normal stresses in the principal directions, and not due to exceeding the shear strength, this method was modified and adapted to the concrete damage plasticity constitutive model. Instead of reducing the failure surface, the parameters which describe the mechanical behavior in the case of uniaxial compression and uniaxial tension were reduced. In this way, the reduction of stress and the corresponding strain was carried out in the entire range of total strain, without changing the shape of the failure surface in the deviator plane. For the proposed methodology, a numerical algorithm was developed and implemented into the software PAK. The algorithm was verified through test examples and the obtained results were compared with analytically calculated FoS. The excellent agreement is observed between the FoS obtained by applying the proposed algorithm and the analytically calculated FoS.

Hydraulic failure presents a significant stability and safety issue for deep shaft excavation projects that deal with a high groundwater table in cohesionless soil. In urban environments, the lowering of the groundwater table for deep shaft excavations is usually not an acceptable solution to mitigate these risks due to the surface settlements it may cause, thus jeopardizing the safety of the surrounding structures. In this paper, a case study of an inlet shaft of a TBM-bored wastewater tunnel in Belgrade, Serbia was analyzed in order to show that grouting techniques can be an appropriate measure for reducing hydraulically induced instability. Since the location of the shaft is near the riverbank, the soil stratigraphy consists of granular soils with a high groundwater table. Several different variations of grout curtains around the shaft were modelled by conducting steady state flow analysis using commercial software based on the finite element method, and the obtained results were used to determine the risk of hydraulically induced failure at the bottom of the excavation. Based on the obtained results it is concluded that the application of grout curtains is a suitable solution for increasing the factor of safety for hydraulic heave problems as well as for soil failure problems. However, when encountering an aquitard layer during the earlier phases of excavation, grout curtains have no effect on lowering the pore pressures that are inducing the uplift at the bottom of the aquitard layer.

In this paper, we presented a methodology for efficient and accurate modeling of water losses in hydraulic tunnels under inside internal water pressure, based on multiple linear regression (MLR). The methodology encompasses all steps needed to obtain an adequate mathematical relation between total water losses and relevant measurements in the tunnel, such as reservoir water level, piezometric levels, concrete and water temperatures, size of cracks, etc. Once the data are preprocessed and input variables were chosen, correlation analysis and PCA (principal component analysis) reduction were performed in order to obtain the pool of regression functions. Through an iterative process, according to stepwise regression principles, the most adequate MLR model in terms of accuracy and complexity was chosen. The methodology presented has been validated in modeling water losses in the hydraulic tunnel under the pressure of PSHPP “Bajina Bašta” in the Republic of Serbia. The obtained results have shown significantly better accuracy compared to the results published by other authors, proving that the developed model can be used as a powerful tool in future analyses of tunnel losses and remediation planning.

A stress-strain history in the material of real concrete structures is usually unknown.An effect of concrete degradation is analyzed to describe how the initial degradation parameter can describe the stress-strain history.The idea is to introduce the initial damage of the structure by the degradation parameter to calculate the internal variables of the constitutive model.Six numerical examples are proposed to verify the methodology for various loading conditions.Based on the obtained results, it was shown that unknown stress-strain history could be successfully represented using the original material parameters and the initial degradation of the concrete.The stress-strain behavior of the damaged concrete is successfully simulated and essential for the structural analysis of civil engineering structures.

Analyses of mechanical, thermal and filtration processes in the large gravity dam and surrounding rock mass were performed and presented. The analyses were conducted within the stability analysis of the dam Djerdap 1. The dam was thoroughly modelled according to the project documentation in order to detect potential flaws or failure of specific parts of dam system. Additionally, it is possible to analyze dam stability during potential failure of specific parts of drainage system. Since the dam lies on a very complex fundament, material characteristics are assigned to each finite element according to geological maps obtained through testing of materials. All the loads influencing the dam in exploitation conditions (mechanical, thermal and filtration loads) are applied to the model. In order to consider the interaction of different processes, a coupled analysis was conducted. After the preliminary FEM analyses, obtained results were compared to the measured values, upon which the input parameters where accordingly corrected. For such adopted input parameters, dam safety factors were calculated in repeated analyses. Model calibration was not performed.

The recycling of waste products and its further use for new products is of the utmost importance nowadays. The quantities of waste product originating from industries involving plastics, paper, wood, textile and metal foils, such as the related automotive, paper, wood and food industries, represent extremely large numbers, strongly indicating the need for efficient waste management. On the other side of things, companies are always looking for ways to lower material costs. The combination of different waste materials can be used for production of new composite materials. This paper will present a brief overview of existing possibilities in the development of new composites completely made of waste materials, as well as further research directions. A preliminary study of material combinations that can provide a composite aimed at load bearing applications is given, for the purpose of replacing elements such as wood blocks in transport pallets. Several combinations of waste material from different industries were studied in a composite structure: paper, cardboard boxes, tetra-pak containers, expanded polystyrene (styrofoam), polyurethane (PU) foam, artificial leather, textile, wood chips and dust. Preliminary compressive tests were performed. The results indicated unsuitable combinations, but also some that provided a stable compact composite which endured high compressive loads. An important result is that such a composite can be made without adding any adhesives. Waste materials from different industries can be efficiently used for new composites, and further study of this is clearly needed.

Knowledge of the deformation properties of the rock mass is essential for the stress–strain analysis of structures such as dams, tunnels, slopes, and other underground structures and the most important parameter of the deformability of the rock mass is the deformation modulus. This paper describes statistical models based on multiple linear regression and artificial neural networks. The models are developed using the test results of the deformation modulus obtained during the construction of the Iron Gate 1 dam on the Danube River and correlate these with measurements of the velocities of longitudinal waves and pressures in the rock mass. The parameters used for defining the models were obtained by in situ testing during dam construction, meaning that scale effects were also taken into account. For the analysis, 47 experimental results from in situ testing of the rock mass were obtained; 38 of these were used for modelling and nine were used for testing of the models. The model based on the artificial neural networks showed better performance in comparison to the model based on multiple linear regression.

A thermal numerical analysis of large infrastructural objects such as dams, bridges, tunnels, buildings, etc., requires the details about the structure geometry, loadings, boundary conditions and carefully determined material parameters. The material parameters obtained by an expert opinion or an experimental identification can vary from the parameters of specific real structure. This can give inadequate results and the significant difference between the measured data and computed results. To overcome this problem, it is necessary to develop and prescribe the methodology for material parameters calibration. In this paper, one possible approach is applied on example of gravity dam. The proposed methodology consists of: 1) the huge dam model reduction to substructures (lamellas) with the best quality of measured data, 2) the material parameters sensitivity analysis, 3) the calibration using intelligent methods (artificial neural networks, genetic algorithms, etc.) and 4) the verification by comparison of numerical analysis of the whole structure using the calibrated parameters and the available measured data.

In the design of a concrete gravity dam, the key problem is to provide adequate stability against sliding due to the operational loads. When a dam is built on a rock mass foundation with complex geology as in the case considered in this paper, the stability analysis problem becomes considerably complicated. The analytical solution of this problem is very difficult or impossible, so it is necessary to use appropriate numerical methods. To solve such a problem in the design of a concrete gravity dam on the Ibar River nearby Kraljevo, an algorithm for elastoplastic material model was adopted and implemented in the program PAK. In order to simulate the gradual loss of stability due to the rock mass strength reduction, the shear strength reduction method was implemented and used. The analysis shows that the calculated safety factor can reach the requirements of stability against the collapse in the deep foundation layers.

This paper presents stability analysis of embankment dam with the surrounding heterogeneous rock mass using finite element method.In order to perform stability analysis of the dam and surrounding rock mass, several elastic-plastic material models for soil are customized and implemented in program package PAK.A 3D FE model of the embankment dam and the surrounding rock mass containing various material distributions according to their real distribution was made.The model includes a wider area around the dam in order to minimize the influence of the boundary conditions.The initial material parameters were determined using the identification of material parameters on the basis of the material from the dam body.Analysed dam is equipped with dam crest displacement transducers, as well as with transducers for the total and pore pressure in the clay core.Certain deviations have been noticed while comparing the measured values of these quantities with the results of the simulation.Since the analysed dam has been in operation for a long time, these deviations from the initial values of the parameters are caused due to the changes of the mechanical properties of materials during the dam operation.These changes are caused by several factors: the settlement of the dam and foundation, flushing of the material in the body of the dam and foundation, load changes, etc.In order to take into account the change of mechanical properties in materials and achieve the results of numerical simulation to describe the behaviour of the dam as close to the real behaviour, the calibration of the material parameters is carried out.Calibration of material parameters was performed using the measured displacements of the dam crest, as well as pore and total pressures in the clay core.Using the calibration we obtain new material parameters which give results of the numerical simulation that are closer to the behaviour of the real dam.In this manner we manage the dam safety and we can predict its future behaviour.

The safety control of dams is based on measurements of parameters of interest such as seepage flows, seepage water clarity, piezometric levels, water levels, pressures, deformations or movements, temperature variations, loading conditions, etc. Interpretation of these large sets of available data is very important for dam health monitoring and it is based on mathematical models. Modelling seepage through geological formations located near the dam site or dam bodies is a challenging task in dam engineering. The objective of this study is to develop a feedforward neural network (FNN) model to predict the piezometric water level in dams. An improved resilient propagation algorithm has been used to train the FNN. The measured data have been compared with the results of FNN models and multiple linear regression (MLR) models that have been widely used in analysis of the structural dam behaviour. The FNN and MLR models have been developed and tested using experimental data collected during 9 years. The results of this study show that FNN models can be a powerful and important tool which can be used to assess dams.