Effect of waste rock inclusions on the seismic stability of an upstream raised tailings impoundment: a numerical investigation

2015 ◽  
Vol 52 (12) ◽  
pp. 1930-1944 ◽  
Author(s):  
Behnam Ferdosi ◽  
Michael James ◽  
Michel Aubertin
Keyword(s):  
Ground Motions ◽  
Low Frequency ◽  
Horizontal Displacement ◽  
Waste Rock ◽  
Seismic Stability ◽  
Environmental Damage ◽  
Total Width ◽  
Tailings Impoundment ◽  
Downstream Slope ◽  
Potential Failure

Over the years, seismic activity has been a relatively common cause of tailings impoundment failure. The flow of liquefied tailings from such ruptures can result in very severe consequences, including loss of life and environmental damage. A co-disposal technique consisting of placing waste rock inclusions in tailings impoundments prior to and during tailings deposition was proposed by the authors. The waste rock is placed to create continuous inclusions within the impoundment, which provide a number of environmental and geotechnical benefits, particularly with respect to seismic stability. The results of numerical simulations previously performed have shown that the UBCSAND model can predict the seismic response of tailings. The UBCSAND constitutive model was used to conduct simulations to evaluate of the use of waste rock inclusions to improve the seismic stability of a tailings impoundment. The evaluation consists of numerical analyses of an actual tailings impoundment as constructed (without inclusions), and then assuming that it was constructed with inclusions, subjected to earthquake loads of various energy contents and with different predominant frequencies. The analyses were conducted in static, seismic, and post-shaking phases. The displacement of the surface of downstream slope of the tailings dyke was recorded during the analyses. The results indicate that the presence of waste rock inclusions can significantly improve the seismic behavior of the impoundment by reducing the displacements of the surface of the downstream slope and the extent of potential failure zones. Also, the results show that in most cases, the influence of a low-frequency earthquake on the displacement of the downstream slope of the tailings dyke is more important than that of a high-frequency earthquake. The performances of the tailings impoundment with different configurations of waste rock inclusions (varying width and center-to-center spacing) were classified based on the average normalized horizontal displacement of the downstream slope (ARx) for a range input ground motions. Charts were then developed to show how ARx is influenced by the total width of inclusions, their spacing, and the input ground motions.

Vector-acoustic full-waveform inversion: Taking advantage of wavefield separation and dealiasing

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. R409-R423
Author(s):  
Polina Zheglova ◽  
Alison Malcolm
Keyword(s):  
Seismic Waves ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Horizontal Displacement ◽  
Displacement Component ◽  
Full Waveform Inversion ◽  
Directional Information ◽  
Wave Separation ◽  
Full Waveform ◽  
Natural Separation

Vector-acoustic full-waveform inversion (VAFWI) directly inverts vector-acoustic (VA) data, which consist of pressure and particle displacement components, at the cost of conventional acoustic full-waveform inversion (FWI). VA data contain information about the direction of arrival of the recorded seismic waves. In VAFWI, this directional information is taken into account by introducing an appropriate data weighting. With this weighting, in the geometry of a marine seismic experiment, the VAFWI adjoint calculation approximates inverse wavefield extrapolation, resulting in the natural separation of up- and downgoing recorded waves. If the free-surface effects are modeled during the inversion, the wave separation leads to (1) suppression of surface-related artifacts, (2) constructive interference of receiver ghosts with their primaries leading to preservation of the low-frequency content in the adjoint fields, and (3) compensation for insufficient spatial wavefield sampling on the receiver side. The horizontal displacement component helps interpolate the missing data. Synthetic examples demonstrate that for undersampled data, VAFWI consistently recovers the subsurface properties with higher resolution and fewer artifacts than conventional FWI.

scholarly journals Assessment of Earthquake Destructive Power to Structures Based on Machine Learning Methods

2020 ◽  
Vol 10 (18) ◽  
pp. 6210
Author(s):  
Ruihao Zheng ◽  
Chen Xiong ◽  
Xiangbin Deng ◽  
Qiangsheng Li ◽  
Yi Li
Keyword(s):  
Neural Network ◽  
Machine Learning ◽  
Ground Motions ◽  
Low Frequency ◽  
Time History ◽  
Time History Analysis ◽  
Machine Learning Algorithms ◽  
Learning Networks ◽  
History Analysis ◽  
Deep Layers

This study presents a machine learning-based method for the destructive power assessment of earthquake to structures. First, the analysis procedure of the method is presented, and the backpropagation neural network (BPNN) and convolutional neural network (CNN) are used as the machine learning algorithms. Second, the optimized BPNN architecture is obtained by discussing the influence of a different number of hidden layers and nodes. Third, the CNN architecture is proposed based on several classical deep learning networks. To build the machine learning models, 50,570 time-history analysis results of a structural system subjected to different ground motions are used as training, validation, and test samples. The results of the BPNN indicate that the features extraction method based on the short-time Fourier transform (STFT) can well reflect the frequency-/time-domain characteristics of ground motions. The results of the CNN indicate that the CNN exhibits better accuracy (R2 = 0.8737) compared with that of the BPNN (R2 = 0.6784). Furthermore, the CNN model exhibits remarkable computational efficiency, the prediction of 1000 structures based on the CNN model takes 0.762 s, while 507.81 s are required for the conventional time-history analysis (THA)-based simulation. Feature visualization of different layers of the CNN reveals that the shallow to deep layers of the CNN can extract the high to low-frequency features of ground motions. The proposed method can assist in the fast prediction of engineering demand parameters of large-number structures, which facilitates the damage or loss assessments of regional structures for timely emergency response and disaster relief after earthquake.

Spatial Variability of Source and Attenuation Characteristics in Large Ground-Motion Datasets

2020 ◽  
Author(s):  
Sreeram Reddy Kotha ◽  
Graeme Weatherill ◽  
Dino Bindi ◽  
Fabrice Cotton
Keyword(s):  
Spatial Variability ◽  
Ground Motion ◽  
Ground Motions ◽  
Low Frequency ◽  
Strong Motion ◽  
Response Spectra ◽  
Large Datasets ◽  
Earthquake Scenarios ◽  
Crustal Earthquakes ◽  
Geographical Regions

<p>Ground-Motion Models (GMMs) characterize the random distributions of ground-motions for a combination of earthquake source, wave travel-path, and the effected site’s geological properties. Typically, GMMs are regressed over a compendium of strong ground-motion recordings collected from several earthquakes recorded at multiple sites scattered across a variety of geographical regions. The necessity of compiling such large datasets is to expand the range of magnitude, distance, and site-types; in order to regress a GMM capable of predicting realistic ground-motions for rare earthquake scenarios, e.g. large magnitudes at short distances from a reference rock site. The European Strong-Motion (ESM) dataset is one such compendium of observations from a few hundred shallow crustal earthquakes recorded at a several hundred seismic stations in Europe and Middle-East.</p><p>We developed new GMMs from the ESM dataset, capable of predicting both the response spectra and Fourier spectra in a broadband of periods and frequencies, respectively. However, given the clear tectonic and geological diversity of the data, possible regional and site-specific differences in observed ground-motions needed to be quantified; whilst also considering the possible contamination of data from outliers. Quantified regional differences indicate that high-frequency ground-motions attenuate faster with distance in Italy compared to the rest of Europe, as well as systematically weaker ground-motions from central Italian earthquakes. In addition, residual analyses evidence anisotropic attenuation of low frequency ground-motions, imitating the pattern of shear-wave energy radiation. With increasing spatial variability of ground-motion data, the GMM prediction variability apparently increases. Hence, robust mixed-effects regressions and residual analyses are employed to relax the ergodic assumption.</p><p>Large datasets, such as the ESM, NGA-West2, and from KiK-Net, provide ample opportunity to identify and evaluate the previously hypothesized event-to-event, region-to-region, and site-to-site differences in ground-motions. With the appropriate statistical methods, these variabilities can be quantified and applied in seismic hazard and risk predictions. We intend to present the new GMMs: their development, performance and applicability, prospective improvements and research needs.</p>

Computational Simulation of the Drilling Vessel Motion and its Effects on the Riser/BOP Connection

2019 ◽  
Author(s):  
Xavier Castello ◽  
José Luis Párraga Quispe ◽  
Segen F. Estefen ◽  
Marcelo Igor Lourenço de Souza ◽  
Nilo de Moura Jorge
Keyword(s):  
Computational Simulation ◽  
Horizontal Displacement ◽  
Environmental Damage ◽  
Marine Riser ◽  
Offshore Drilling ◽  
Propagating Waves ◽  
Drilling Operations ◽  
Heave Motion ◽  
Vessel Motion ◽  
Typical Scenario

Abstract During subsea offshore drilling operations, the floating vessel is connected to the wellhead through a series of equipment assemblies. The riser is exposed to dynamic loads from currents, waves, and drilling platform motions. Therefore, a dynamic analysis of the riser system is required to obtain forces and moments in the wellhead. It is even more important in dynamic positioning (DP) operations, where the knowledge of boundary conditions for a safe emergency disconnection is highly relevant. The objective of this paper is to calculate the effects of changing the light and older BOP (typically with 4 rams) for newer and heavier BOPs (after Macondo accident, with 6 rams) on the Emergency Disconnect Sequence (EDS) time and on wellhead equipment strength. A typical scenario of drilling is proposed, in which the marine riser system considers the drilling string, the lower flex-joint, the marine riser, the kill and choke lines and the tensioners. Tensioners are used to top tension the marine riser and to compensate relative heave motion between the riser and the floating vessel. Riser systems were designed using the API RP 16Q and simulated using Orcaflex software. Vessel dynamic motions were calculated according to the response amplitude operator (RAO) data from a typical offshore drilling semi-submersible. The vessel motion is superimposed by a drift-off motion, which consists of a horizontal displacement along time in the direction of the propagating waves. It is employed to simulate the condition of vessel position loss due to thruster and or control system failure. Results indicate that the use of heavier BOPs reduces significantly the available time for initiating the EDS. Results are worse if older generation of wellhead equipment is used, where a smaller drift-off is necessary to safely disconnect the riser before potential equipment and environmental damage occurs.

scholarly journals Application of microtremor HVSR method for preliminary assessment of seismic site effect in Ngipik landfill, Gresik

2018 ◽  
Vol 195 ◽  
pp. 03017
Author(s):  
Siti Nurlita Fitri ◽  
Ria Asih Aryani Soemitro ◽  
Dwa Dewa Warnana ◽  
Nila Sutra
Keyword(s):  
Stability Analysis ◽  
Ground Motions ◽  
Protective Layer ◽  
Site Effect ◽  
Vulnerability Index ◽  
Seismic Stability ◽  
Predominant Frequency ◽  
Preliminary Assessment ◽  
Hvsr Method ◽  
Open Dumping

This paper presents an investigation based on affected areas of earthquakes based on the micro-tremor horizontal-to-vertical ratio (HVSR) method around the Ngipik Landfill, Gresik. Ngipik landfill applies an Open dumping system with no protective layer to prevent groundwater pollution. Hence, the effect of the earthquake was investigated for preliminary assessment of leachate’s leakage. The micro-tremor measurements were performed by dividing the area into a grid with a 25m distance. The predominant frequency (f0) ranges between 1.1 and 3.65 Hz and the peak of HVSR (Am) varies from 2.04 to 7.16. The vulnerability index (kg) displayed the level of soil damage due to ground motions; the highest kg values signified the weaker zones during earthquakes and also indicated the leachate spread. The result of this paper might consider to seismic stability analysis of leachate recirculation landfill.

scholarly journals Across-fault ground motions and their effects on some bridges in the 1999 Chi-Chi earthquake

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Yuanzheng Lin ◽  
Zhouhong Zong ◽  
Jin Lin ◽  
Yale Li ◽  
Yiyan Chen
Keyword(s):  
Ground Motions ◽  
Low Frequency ◽  
Stochastic Method ◽  
Collapse Mechanism ◽  
Simply Supported ◽  
Collapse Mechanisms ◽  
Finite Fault ◽  
Structural Responses ◽  
Frequency Components ◽  
Explicit Dynamic

AbstractSimply-supported bridges are vulnerable to surface fault rupture as evidenced by several fault-crossing bridges in the 1999 Chi-Chi earthquake. To investigate the seismic collapse mechanism of simply-supported bridges crossing the fault, across-fault ground motions are firstly simulated in the present study. In particular, based on a previously developed fault model of the 1999 Chi-Chi earthquake, broadband across-fault ground motions at six fault-crossing bridges are simulated using the hybrid deterministic-stochastic method, in which the low- and high-frequency components are computed using the deterministic Green’s function method and the stochastic finite-fault modeling method, respectively. The simulation results indicate that the hybrid deterministic-stochastic method can give reasonable predictions to the across-fault ground motions. Furthermore, utilizing the explicit dynamic finite element (FE) code LS-DYNA, behaviors of a three-span simply-supported bridge under a selected pair of across-fault ground motions are numerically simulated. Numerical results indicate that the structural responses and collapse mechanisms are dominated by the low-frequency ground motions. The large differential static offset across the fault is the main reason for the collapse of the simply-supported bridges. This study contributes understandings for the across-fault ground motions and the collapse mechanism of some bridges in the 1999 Chi-Chi earthquake.

Deformation of Steel Straight Pipes With Internal Pressure Under Axial Compression and Bending Load by Seismic Action

2008 ◽  
Author(s):  
He´ctor A. Sa´nchez Sa´nchez ◽  
Carlos Corte´s Salas
Keyword(s):  
Internal Pressure ◽  
Large Deformations ◽  
Ground Motions ◽  
Horizontal Displacement ◽  
Seismic Action ◽  
Bending Stress ◽  
Buried Pipelines ◽  
Straight Pipe ◽  
Bending Effect ◽  
Bending Load

Due to the high risk seismic in many zones of Mexico it has been observed that the ground motions often show large horizontal displacement. This displacement causes large deformations of buried pipelines. Then, the knowledge of study and design recommendations related to deformability of the pipes has not been sufficiently provided. A grand number of studies have been reported concerned about the plastic deformations or buckling of the straight pipe. Most of them are performance of column pipe without internal pressure. Therefore, in this work are analyzed the steel straight pipes, for the purpose of clarifying the deformations of the pipes with internal pressure under large displacement and bending. Effect of internal pressure on deformability of pipe is investigated both under load bending. Stress analysis using FEM is performed in order to simulate the large deformations of the pipes.

Numerical investigation of the influence of waste rock inclusions on tailings consolidation

2014 ◽  
Vol 51 (9) ◽  
pp. 1021-1032 ◽  
Author(s):  
Frédérick L.Bolduc ◽  
Michel Aubertin
Keyword(s):  
Cross Section ◽  
Hard Rock ◽  
Waste Rock ◽  
Mine Wastes ◽  
Compression Index ◽  
Tailings Impoundment ◽  
Pore Water Pressures ◽  
Zone Of Influence ◽  
Main Factors ◽  
Hard Rock Mines

The construction of waste rock inclusions (WRIs) in a tailings impoundment constitutes an alternative disposal technique that aims at improving the management of mine wastes. This technique consists in strategically placing the WRIs inside the impoundment, at the beginning and during its operation, to form compartments (or cells) in which the tailings are stored. Such inclusions can serve various purposes. In this paper, the authors investigate the effects of drainage from WRIs on tailings consolidation during filling of the impoundment, using experimental data from hard rock mines that provide the hydrogeological and geotechnical properties introduced in the numerical analyses. The model used for the simulations represents a cross section of a portion of a tailings impoundment containing a WRI. The numerical calculations results illustrate how the WRI affects the dissipation of the excess pore water pressures (PWPs) during filling of the impoundment, and help quantify the extent of the zone of influence of the inclusion. The results from the parametric analysis show that the saturated hydraulic conductivity ksat, compression index Cc, thickness, and deposition rate of the tailings are the main factors that affect the efficiency of WRIs to accelerate dissipation of excess PWPs. The discussion that follows recalls the main limitations of this investigation and addresses practical aspects related to the WRIs technique.

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