Srđan Kostić

Predictions of Experimentally Observed Stochastic Ground Vibrations Induced by Blasting

In the present paper, we investigate the blast induced ground motion recorded at the limestone quarry “Suva Vrela” near Kosjerić, which is located in the western part of Serbia. We examine the recorded signals by means of surrogate data methods and a determinism test, in order to determine whether the recorded ground velocity is stochastic or deterministic in nature. Longitudinal, transversal and the vertical ground motion component are analyzed at three monitoring points that are located at different distances from the blasting source. The analysis reveals that the recordings belong to a class of stationary linear stochastic processes with Gaussian inputs, which could be distorted by a monotonic, instantaneous, time-independent nonlinear function. Low determinism factors obtained with the determinism test further confirm the stochastic nature of the recordings. Guided by the outcome of time series analysis, we propose an improved prediction model for the peak particle velocity based on a neural network. We show that, while conventional predictors fail to provide acceptable prediction accuracy, the neural network model with four main blast parameters as input, namely total charge, maximum charge per delay, distance from the blasting source to the measuring point, and hole depth, delivers significantly more accurate predictions that may be applicable on site. We also perform a sensitivity analysis, which reveals that the distance from the blasting source has the strongest influence on the final value of the peak particle velocity. This is in full agreement with previous observations and theory, thus additionally validating our methodology and main conclusions.

Slope Stability Analysis Based on Experimental Design

AbstractIn this paper, the authors propose an analytical model for the prediction of the slope safety factor as a function of basic geometrical parameters (slope height H and slope angle β) and soil factors (bulk density γ, cohesion c, angle of internal friction φ, and pore water pressure coefficient ru). Research was performed by applying the statistical technique of experimental design, for which the input data were provided by stability analyses of different homogeneous slopes with a circular slip surface using the Spencer limit equilibrium method. The proposed model represents a nonlinear equation of a simpler form and higher prediction accuracy than those of the existing mathematical expressions, with predominant linear effect of the individual factors and significant influence of the two-factor interactions. Linear terms in a derived equation indicate a positive effect of c or φ and a negative effect of H, β, γ, or ru on slope stability. Because of two-factor interactions, the effect of c is highly ...

Stability of earth slopes under the effect of main environmental properties of weathered clay–marl deposits in Belgrade (Serbia)

In the present paper, the impact of the main environmental factors on slope stability is analyzed by deriving a model for slope safety factor as a nonlinear function of geomechanical soil properties (bulk density γ, cohesion c, angle of internal friction φ and pore water pressure coefficient ru) and terrain geometry (slope height H, bedrock depth d and slope angle β). The suggested model is derived using the response surface method, based on Spencer’s stability analyses of homogeneous slopes with circular slip surface. The analyzed parameter ranges were chosen according to the commonly determined values for unstable slopes in Neogene clay–marl deposits in Belgrade. The statistical reliability of the suggested model was confirmed by analyzing the stability of slopes with random geomechanical soil properties and terrain geometry. The obtained results indicate that all the examined environmental factors have statistically significant impact on the slope stability with prevailing linear effect, while geometrical factors and cohesion also show substantial quadratic effect. The existence of two-factor interactions imply that the impact of slope height on its stability is strongly dependent on slope angle, cohesion and bedrock depth, while the latter two also significantly affect the impact of slope angle on Fs.

Robust optimization of concrete strength estimation using response surface methodology and Monte Carlo simulation

ABSTRACT A new approach is proposed for the robust optimization of concrete strength estimation using response surface methodology and Monte Carlo simulation. The essence of the suggested procedure lies in the reliable prediction of concrete strength as a simple function of unit mass, water/cement ratio, age and superplasticizer content. The derived model provides sufficiently accurate results for the calibration and verification phases, the latter of which is conducted using data that were not used for model development. The results of additional analysis indicate that residuals in the calibration and verification stages have a normal distribution. Is its also shown that the uncertainty of estimated coefficient values has a statistically insignificant effect on concrete strength, confirming the reliability of the proposed model. Moreover, analysis of the effect of laboratory measurement errors indicates the robustness of concrete compressive strength against the variation in measured parameter values.

Complex Dynamics of Landslides with Time Delay Under External Seismic Triggering Effect

In present paper, model of infinite creeping slope with Dieterich-Ruina rate-and state-dependent friction law is analyzed using methods of nonlinear dynamics. The model is examined under the variation of two parameters: time delay t d and initial shear stress s 0. Time delay describes the memory effect of the sliding surface and it is generally considered as a function of history of sliding. Initial stress parameter is periodically perturbed, corresponding to long duration shear seismic wave, or it could be generated by non-natural sources such as traffic vibrations. The co-action of the observed parameters is estimated for two different regimes of sliding, namely β 1, where β denotes the ratio of long-term to short-term (immediate) stress change. The results of the analysis indicate that the most complex dynamics occurs for β 1, system exhibits chaotic dynamics for t d = 0.1 and for δ s ≤ 0.18. These results correspond well with the previous experimental observations on clay and siltstone with low clay fraction, indicating that the motion along the sliding surface is velocity-strengthening (β < 1).

Complex Dynamics of Spring-Block Earthquake Model Under Periodic Parameter Perturbations

A simple model of earthquake nucleation that may account for the onset of chaotic dynamics is proposed and analyzed. It represents a generalization of the Burridge–Knopoff single-block model with Dieterich–Ruinas rate- and state-dependent friction law. It is demonstrated that deterministic chaos may emerge when some of the parameters are assumed to undergo small oscillations about their equilibrium values. Implementing the standard numerical methods from the theory of dynamical systems, the analysis is carried out for the cases having one or two periodically variable parameters, such that the appropriate bifurcation diagrams, phase portraits, power spectra, and the Lyapunov exponents are obtained. The results of analysis indicate two different scenarios to chaos. On one side, the Ruelle–Takens–Newhouse route to chaos is observed for the cases of limit amplitude perturbations. On the other side, when the angular frequency is assumed constant for the value near the periodic motion of the block in an unperturbed case, variation of oscillation amplitudes probably gives rise to global bifurcations, with immediate occurrence of chaotic behavior. Further analysis shows that chaotic behavior emerges only for small oscillation frequencies and higher perturbation amplitudes when two perturbed parameters are brought into play. If higher oscillation frequencies are assumed, no bifurcation occurs, and the system under study exhibits only the periodic motion. In contrast to the previous research, the onset of chaos is observed for much smaller values of the stress ratio parameter. In other words, even the relatively small perturbations of the control parameters could lead to deterministic chaos and, thus, to instabilities and earthquakes.