A borehole stability study by newly designed laboratory tests on thick-walled hollow cylinders
- Authors: Hashemi, Sam , Melkoumian, Nouné , Taheri, Abbas
- Date: 2015
- Type: Text , Journal article
- Relation: Journal of Rock Mechanics and Geotechnical Engineering Vol. 7, no. 5 (2015), p. 519-531
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- Description: At several mineral exploration drilling sites in Australia, weakly consolidated formations mainly consist of sand particles that are poorly bonded by cementing agents such as clay, iron oxide cement or calcite. These formations are being encountered when drilling boreholes to the depth of up to 200 m. To study the behaviour of these materials, thick-walled hollow cylinder (TWHC) and solid cylindrical synthetic specimens were designed and prepared by adding Portland cement and water to sand grains. The effects of different parameters such as water and cement contents, grain size distribution and mixture curing time on the characteristics of the samples were studied to identify the mixture closely resembling the formation at the drilling site. The Hoek triaxial cell was modified to allow the visual monitoring of grain debonding and borehole breakout processes during the laboratory tests. The results showed the significance of real-time visual monitoring in determining the initiation of the borehole breakout. The size-scale effect study on TWHC specimens revealed that with the increasing borehole size, the ductility of the specimen decreases, however, the axial and lateral stiffnesses of the TWHC specimen remain unchanged. Under different confining pressures the lateral strain at the initiation point of borehole breakout is considerably lower in a larger size borehole (20 mm) compared to that in a smaller one (10 mm). Also, it was observed that the level of peak strength increment in TWHC specimens decreases with the increasing confining pressure. © 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.
A century-scale, human-induced ecohydrological evolution of wetlands of two large river basins in Australia (Murray) and China (Yangtze)
- Authors: Kattel, Giri , Dong, Xuhui , Yang, Xiangdong
- Date: 2016
- Type: Text , Journal article , Review
- Relation: Hydrology and Earth System Sciences Vol. 20, no. 6 (2016), p. 2151-2168
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- Description: Recently, the provision of food and water resources of two of the world's largest river basins, the Murray and the Yangtze, has been significantly altered through widespread landscape modification. Long-term sedimentary archives, dating back for some centuries from wetlands of these river basins, reveal that rapid, basin-wide development has reduced the resilience of biological communities, resulting in considerable decline in ecosystem services, including water quality. Large-scale human disturbance to river systems, due to river regulation during the mid-20th century, has transformed the hydrology of rivers and wetlands, causing widespread modification of aquatic biological communities. Changes to cladoceran zooplankton (water fleas) were used to assess the historical hydrology and ecology of three Murray and Yangtze river wetlands over the past century. Subfossil assemblages of cladocerans retrieved from sediment cores (94, 45, and 65 cm) of three wetlands: Kings Billabong (Murray), Zhangdu, and Liangzi lakes (Yangtze), showed strong responses to hydrological changes in the river after the mid-20th century. In particular, river regulation caused by construction of dams and weirs together with river channel modifications, has led to significant hydrological alterations. These hydrological disturbances were either (1) a prolonged inundation of wetlands or (2) reduced river flow, both of which caused variability in wetland depth. Inevitably, these phenomena have subsequently transformed the natural wetland habitats, leading to a switch in cladoceran assemblages to species preferring poor water quality, and in some cases to eutrophication. The quantitative and qualitative decline of wetland water conditions is indicative of reduced ecosystem services, and requires effective restoration measures for both river basins which have been impacted by recent socioeconomic development and climate change. © 2016 Author(s).
A comparative study on the application of various artificial neural networks to simultaneous prediction of rock fragmentation and backbreak
- Authors: Sayadi, Ahmad , Monjezi, Masoud , Talebi, Nemat , Khandelwal, Manoj
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Rock Mechanics and Geotechnical Engineering Vol. 5, no. 4 (2013), p. 318-324
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- Description: In blasting operation, the aim is to achieve proper fragmentation and to avoid undesirable events such as backbreak. Therefore, predicting rock fragmentation and backbreak is very important to arrive at a technically and economically successful outcome. Since many parameters affect the blasting results in a complicated mechanism, employment of robust methods such as artificial neural network may be very useful. In this regard, this paper attends to simultaneous prediction of rock fragmentation and backbreak in the blasting operation of Tehran Cement Company limestone mines in Iran. Back propagation neural network (BPNN) and radial basis function neural network (RBFNN) are adopted for the simulation. Also, regression analysis is performed between independent and dependent variables. For the BPNN modeling, a network with architecture 6-10-2 is found to be optimum whereas for the RBFNN, architecture 6-36-2 with spread factor of 0.79 provides maximum prediction aptitude. Performance comparison of the developed models is fulfilled using value account for (VAF), root mean square error (RMSE), determination coefficient (R2) and maximum relative error (MRE). As such, it is observed that the BPNN model is the most preferable model providing maximum accuracy and minimum error. Also, sensitivity analysis shows that inputs burden and stemming are the most effective parameters on the outputs fragmentation and backbreak, respectively. On the other hand, for both of the outputs, specific charge is the least effective parameter. © 2013 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.
A scaled boundary finite element formulation with bubble functions for elasto-static analyses of functionally graded materials
- Authors: Ooi, Ean Tat , Song, Chongmin , Natarajan, Sundararajan
- Date: 2017
- Type: Text , Journal article
- Relation: Computational Mechanics Vol. 60, no. 6 (2017), p. 943-967
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- Description: This manuscript presents an extension of the recently-developed high order complete scaled boundary shape functions to model elasto-static problems in functionally graded materials. Both isotropic and orthotropic functionally graded materials are modelled. The high order complete properties of the shape functions are realized through the introduction of bubble-like functions derived from the equilibrium condition of a polygon subjected to body loads. The bubble functions preserve the displacement compatibility between the elements in the mesh. The heterogeneity resulting from the material gradient introduces additional terms in the polygon stiffness matrix that are integrated analytically. Few numerical benchmarks were used to validate the developed formulation. The high order completeness property of the bubble functions result in superior accuracy and convergence rates for generic elasto-static and fracture problems involving functionally graded materials. © 2017, Springer-Verlag GmbH Germany.
A shared bus profiling scheme for smart cities based on heterogeneous mobile crowdsourced data
- Authors: Kong, Xiangjie , Xia, Feng , Li, Jianxin , Hou, Mingliang , Li, Menglin , Xiang, Yong
- Date: 2020
- Type: Text , Journal article
- Relation: IEEE Transactions on Industrial Informatics Vol. 16, no. 2 (2020), p. 1436-1444
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- Description: Mobile crowdsourcing (MCS), as an effective and crucial technique of Industrial Internet of Things, is enabling smart city initiatives in the real world. It aims at incorporating the intelligence of dynamic crowds to collect and compute decentralized ubiquitous sensing data that can be used to solve major urbanization problems such as traffic congestion. The shared bus, as a neotype transportation mode, aims at improving the resource utilization rate and maintaining the advantages of convenience and economy. In this article, we provide a scheme to profile shared buses through heterogeneous mobile crowdsourced data (TRProfiling). First, we design an MCS-based shared bus data generation and collection solution to overcome the aforementioned data scarcity issue. Then, we propose a travel profiling to profile resident travel and design a method called multiconstraint evolution algorithm to optimize the routes. Experimental results demonstrate that TRProfiling has an excellent performance in satisfying passengers' travel requirements. © 2005-2012 IEEE.
A surrogate model for interference prevention in the limaçon-to-limaçon machines
- Authors: Sultan, Ibrahim
- Date: 2007
- Type: Text , Journal article
- Relation: Engineering Computations (Swansea, Wales) Vol. 24, no. 5 (2007), p. 437-449
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- Description: Purpose - This paper aims to replace the complicated iterative procedure used to prevent interference in limacon-to-limacon machines by a simplified mathematical equation which can be solved by a straightforward substitution of the required clearance value. Design/methodology/approach - The input data to the iterative procedure and the obtained results have been employed in regression models to construct the sought after equation. Searching for a proper form of this equation involved numerical experiments to study the effects of the various model parameters on the system response. Findings - The numerical experiments conducted proved to be an effective model construction technique, and the regression model proposed has been found extremely accurate in the specified parameter space. Research limitations/implications - The proposed equation is applicable within the parameter range chosen for the study. This range is the one often used for industrial applications. Should the parameters selected for a specific design fall outside the specified range, the proposed model structure may have to be varied to maintain a desirable level of accuracy. Practical implications - The interference study is a part of the iterative procedure employed to design the dimensions of the limaçon-to-limaçon machine. This iterative procedure searches for the proper design amongst hundreds of various possible solutions. The results of this paper will ensure a much faster convergence for the design procedure, since the interference study will be eliminated from the iterative section of the analysis. Originality/value - The paper offers a valid and accurate model that can be efficiently used for the intended purpose. © Emerald Group Publishing Limited.
- Description: C1
- Description: 2003004799
An investigation of correlation factors linking footing resistance on sand with cone penetration test results
- Authors: Gavin, Kenneth , Tolooiyan, Ali
- Date: 2012
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 46, no. (2012), p. 84-92
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- Description: Significant research effort has led to improvements in our ability to estimate the ultimate bearing resistance of footings in sand. These techniques often estimate the footing resistance at relatively large displacements, typically 10% of the footing width, q b0.1. Cone Penetration Test (CPT) design methods typically link q b0.1 and q c through a constant reduction factor, α. A range of α factors for shallow footings have been proposed, some methods suggest that α is constant and while others that it varies with footing width and depth (or stress level). There is a dearth of field data with which to compare these correlation factors, in particular where foundation width and depth have been varied in the same ground conditions. For this reason finite element analyses have proven to be a useful tool for performing the parametric studies required to asses factors controlling α. This paper describes the results of numerical analyses performed to investigate α factors for soil profiles which were calibrated using the results of the CPT tests performed at a dense sand test-bed site. The numerical model was first used to perform parametric analyses to consider the effect of footing width, B and footing depth, D on the α factor mobilised in dense Blessington sand. In order to assess the effects of relative density, footing tests in a range of natural sands with variable in situ densities were modeled. The results of the finite element analyses suggest that a direct correlation between q b0.1 and q c can be established at a given test site which is independent of footing width and depth and is relatively weakly dependent on the sands relative density if the zone of influence of the foundation considered is large enough. © 2012 Elsevier Ltd.
Automated health condition diagnosis of in situ wood utility poles using an intelligent non-destructive evaluation (NDE) framework
- Authors: Yu, Yang , Subhani, Mahbube , Hoshyar, Azadeh , Li, Jianchun , Li, Huan
- Date: 2020
- Type: Text , Journal article
- Relation: International Journal of Structural Stability and Dynamics Vol. 20, no. 10 (2020), p.
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- Description: Wood utility poles are widely applied in power transmission and telecommunication systems in Australia. Because of a variety of external influence factors, such as fungi, termite and environmental conditions, failure of poles due to the wood degradation with time is of common occurrence with high degree uncertainty. The pole failure may result in serious consequences including both economic and public safety. Therefore, accurately and timely identifying the health condition of the utility poles is of great significance for economic and safe operation of electricity and communication networks. In this paper, a novel non-destructive evaluation (NDE) framework with advanced signal processing and artificial intelligence (AI) techniques is developed to diagnose the condition of utility pole in field. To begin with, the guided waves (GWs) generated within the pole is measured using multi-sensing technique, avoiding difficult interpretation of various wave modes which cannot be detected by only one sensor. Then, empirical mode decomposition (EMD) and principal component analysis (PCA) are employed to extract and select damage-sensitive features from the captured GW signals. Additionally, the up-to-date machine learning (ML) techniques are adopted to diagnose the health condition of the pole based on selected signal patterns. Eventually, the performance of the developed NDE framework is evaluated using the field testing data from 15 new and 24 decommissioned utility poles at the pole yard in Sydney. © 2020 World Scientific Publishing Company.
- Description: This research is supported by Australian Research Council via Linkage Project (LP110200162) and Industrial Transforming Research Hub for Nanoscience Based Construction Materials Manufacturing (IH150100006) as well as Ausgrid. The authors greatly appreciate the ¯nancial and technical supports from the funding bodies.
Boundary element analysis of fatigue crack growth for CFRP-strengthened steel plates with longitudinal weld attachments
- Authors: Yu, Qian Qian , Chen, Tao , Gu, Xiang Lin , Zhao, Xiao Ling , Xiao, Zhigang
- Date: 2015
- Type: Text , Journal article
- Relation: Journal of Composites for Construction Vol. 19, no. 2 (2015), p. 1-12
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- Description: In this paper, steel plates with longitudinal weld attachments strengthened by carbon fiber reinforced polymer (CFRP) laminates on one side were analyzed based on the boundary element method and compared with test data from the literature. Good agreement with the data indicated that the numerical analysis was reliable for estimation of the fatigue crack propagation of CFRP-bonded steel plates with longitudinal weld attachments. The effects of double-sided strengthening, double-sided weld attachment and CFRP stiffness on the fatigue behavior of retrofitted welded joints were also investigated. The results showed that double-sided strengthening was much more efficient than single-sided application. It was observed that the crack propagation of steel plates with weld attachments on both sides was accelerated compared with those with attachments on only one side. In comparison with steel plates without a weld attachment, the retrofitting efficiency, in terms of the fatigue life extension ratio, was significantly lowered in welded plates with single-sided repair, whereas only a slight difference was observed in those with double-sided strengthening. The effect of an increased modulus of the composite materials could result in better fatigue performance, especially with double-sided application. © 2014 American Society of Civil Engineers.
Capillary effect on water table fluctuations in unconfined aquifers
- Authors: Kong, Jun , Shen, Cheng-Ji , Xin, Pei , Song, Zhiyao , Li, Ling , Barry, David , Jeng, Dong-Shen , Stagnitti, Frank , Lockington, David , Parlange, Jean Yves
- Date: 2013
- Type: Text , Journal article
- Relation: Water Resources Research Vol. 49, no. 5 (2013), p. 3064-3069
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- Description: Parlange and Brutsaert (1987) derived a modified Boussinesq equation to account for the capillary effect on water table dynamics in unconfined aquifers. Barry et al. (1996) solved this equation subject to a periodic boundary condition. Their solution shows significant influence of capillarity on water table fluctuations, which evolve to finite-amplitude standing waves at the high frequency limit. Here we propose a new governing equation for the water table, which considers both horizontal and vertical flows in an unsaturated zone of finite thickness. An approximate analytical solution for periodic water table fluctuations based on the new equation was derived. In agreement with previous results, the analytical solution shows that the unsaturated zone's storage capacity permits water table fluctuations to propagate more readily than predicted by the Boussinesq equation. Furthermore, the new solution reveals a capping effect of the unsaturated zone on both the amplitude and phase of the water table fluctuations as well as the water table overheight. Due to the finite thickness of the unsaturated zone, the capillary effect on water table fluctuations is modified mainly with reduced amplitude damping and phase shift. ©2013. American Geophysical Union. All Rights Reserved.
- Description: 2003011129
CFRP Shear Strengthening of Reinforced-Concrete T-Beams with Corroded Shear Links
- Authors: Qin, Shunde , Dirar, Samir , Yang, Jian , Chan, Andrew , Elshafie, Mohammed
- Date: 2015
- Type: Text , Journal article
- Relation: Journal of Composites for Construction Vol. 19, no. 5 (2015), p.
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- Description: This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.
Characterization of the subsurface architecture and identification of potential groundwater paths in a clay-rich floodplain using multi-electrode resistivity imaging
- Authors: Guinea, Ander , Hollins, Suzanne , Meredith, Karina , Hankin, Stuart , Cendón, Dioni
- Date: 2018
- Type: Text , Journal article
- Relation: Hydrological Sciences Journal Vol. 63, no. 6 (2018), p. 909-925
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- Description: The interaction between surface water and groundwater in clay-rich fluvial environments can be complex and is generally poorly understood. Airborne electromagnetic surveys are often used for characterizing regional groundwater systems, but they are constrained by the resolution of the method. A resistivity imaging survey has been carried out in the Macquarie Marshes (New South Wales, Australia) in combination with water chemical sampling. The results have enabled the identification of buried palaeochannels and the location of potential recharge points. The data have been compared with previously published airborne electromagnetic data in the same area. Deeper less conductive features suggest that there is a potential connection between the Great Artesian Basin and groundwater contained within the shallow sand aquifer. Even though the chemistry of the groundwater samples does not indicate interaction with the Great Artesian Basin, the observed discontinuity in the saprolite implies potential for this to happen in other locations.
Deformation behaviour of geotechnical materials with gas bubbles and time dependent compressible organic matter
- Authors: Liu, Kan , Xue, Jianfeng , Yang, Min
- Date: 2016
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 213, no. (2016), p. 98-106
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- Description: Geotechnical materials may contain organic matters and gas bubbles during the process of their formation. The existence of compressible gas bubbles and organic matters may affect the excess pore water pressure distribution during compression and the deformation behaviour of the materials. Immediate settlement and creep have been observed in the early stage of consolidation curves of brown coal and peat samples, which can not be explained with Terzaghi's consolidation theory where soils are considered as fully saturated and soil particles are incompressible. A numerical model has been developed to model the consolidation behaviour of brown coal and peat considering the inclusion of gas bubbles and the time dependent compressible organic matters. In the model, the materials are assumed to contain incompressible minerals, compressible organic matters, gas bubbles and water. Consolidation of the materials is considered as a coupling process of water extrusion and volume variation of gas bubbles and organic matters. The model has been validated using the experimental results from one dimensional consolidation curves of brown coal and historical test results of peat. The gas content and the compressibility of organic matters can be obtained using the proposed model. The model can be used to analyze compression behaviour of geotechnical materials containing compressible particles and gas bubbles.
- Description: Geotechnical materials may contain organic matters and gas bubbles during the process of their formation. The existence of compressible gas bubbles and organic matters may affect the excess pore water pressure distribution during compression and the deformation behaviour of the materials. Immediate settlement and creep have been observed in the early stage of consolidation curves of brown coal and peat samples, which can not be explained with Terzaghi's consolidation theory where soils are considered as fully saturated and soil particles are incompressible. A numerical model has been developed to model the consolidation behaviour of brown coal and peat considering the inclusion of gas bubbles and the time dependent compressible organic matters. In the model, the materials are assumed to contain incompressible minerals, compressible organic matters, gas bubbles and water. Consolidation of the materials is considered as a coupling process of water extrusion and volume variation of gas bubbles and organic matters. The model has been validated using the experimental results from one dimensional consolidation curves of brown coal and historical test results of peat. The gas content and the compressibility of organic matters can be obtained using the proposed model. The model can be used to analyze compression behaviour of geotechnical materials containing compressible particles and gas bubbles. © 2016 Elsevier B.V.
Design of subsea cables/umbilicals for in-service abrasion - part 1 : case studies
- Authors: Reda, Ahmed , Thiedeman, James , Elgazzar, Mohamed , Shahin, Mohamed , Sultan, Ibrahim , McKee, Kristoffer
- Date: 2021
- Type: Text , Journal article
- Relation: Ocean Engineering Vol. 234, no. (2021), p.
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- Description: Submarine cables play a vital role in a myriad of industries around the globe, including power transmission and communication. Failure of submarine cables can have significant economic and technical implications worldwide. Current design methods for submarine cables focus on the ultimate limit states that address the cables structural integrity and on-bottom stability. However, abrasion of the outer protective layers (i.e. yarn and extruded sheaths) can progressively lead to damage and failure of submarine cables when the integrity of the armour sheathing is compromised. This paper documents several case studies of severe abrasion of submarine cables/umbilicals and undertaken corrective measures. The paper also presents some guidelines to be considered in the design process of submarine cables concerning abrasion. The findings of this paper suggest that abrasion should be considered a limit state that must be addressed in the design process of submarine cables and umbilicals. A detailed analysis of the underlying abrasion failure mechanisms is presented and explained in a companion paper (i.e., Part II: Mechanisms). © 2021 Elsevier Ltd
Design of subsea cables/umbilicals for in-service abrasion - part 2 : mechanisms
- Authors: Reda, Ahmed , Elgazzar, Mohamed , Thiedeman, James , McKee, Kristoffer , Sultan, Ibrahim , Shahin, Mohamed
- Date: 2021
- Type: Text , Journal article
- Relation: Ocean Engineering Vol. 234, no. (2021), p.
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- Description: This paper is the second of two companion papers about the design of subsea cables/umbilicals for in-service abrasion. Several case studies of severe abrasion of submarine cables/umbilicals and corrective measures undertaken have been documented and presented in the first paper (Part I: Case Studies). The mechanisms of failure due to abrasion are explained in this paper. The effect of repeated lateral movement on LLDPE (linear low-density polyethylene) extruded outer sheaths of two cable samples was investigated. In the first test, a cable sample was displaced the equivalent of 12 km over a crushed mineral aggregate while in the second test, a cable was subjected to 3 km of displacement under conditions that replicated the touchdown point of a dynamic cable. The results of the first test indicated that the overall abrasion was low and acceptable. In the second test however, the outer sheath was completely worn through. The authors recommend the thickness of the outer sheath be increased for cables where uniform abrasion is expected, and high abrasion protection units be employed where localized abrasion is expected. Empirical data is provided to support these recommendations. © 2021 Elsevier Ltd
Developing a hybrid model of Jaya algorithm-based extreme gradient boosting machine to estimate blast-induced ground vibrations
- Authors: Zhou, Jian , Qiu, Yingui , Khandelwal, Manoj , Zhu, Shuangli , Zhang, Xiliang
- Date: 2021
- Type: Text , Journal article
- Relation: International Journal of Rock Mechanics and Mining Sciences Vol. 145, no. (2021), p.
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- Description: Blasting is still being considered to be one the most important applicable alternatives for conventional excavations. Ground vibration generated due to blasting is an undesirable phenomenon which is harmful for the nearby structures and should be prevented. In this regard, a novel intelligent approach for predicting blast-induced PPV was developed. The distinctive Jaya algorithm and high efficient extreme gradient boosting machine (XGBoost) were applied to obtain the goal, called the Jaya-XGBoost model. Accordingly, 150 sets of data composed of 13 controllable and uncontrollable parameters are chosen as input independent variables and the measured peak particle velocity (PPV) is chosen as an output dependent variable. Also, the Jaya algorithm was used for optimization of hyper-parameters of XGBoost. Additionally, six empirical models and several machine learning models such as XGBoost, random forest, AdaBoost, artificial neural network and Bagging were also considered and applied for comparison of the proposed Jaya-XGBoost model. Accuracy criteria including determination coefficient (R2), root-mean-square error (RMSE), mean absolute error (MAE), and the variance accounted for (VAF) were used for the assessment of models. For this study, 150 blasting operations were analyzed. Also, the Shapley Additive Explanations (SHAP) method is used to interpret the importance of features and their contribution to PPV prediction. Findings reveal that the proposed Jaya-XGBoost emerged as the most reliable model in contrast to other machine learning models and traditional empirical models. This study may be helpful to mining researchers and engineers who use intelligent machine learning algorithms to predict blast-induced ground vibration. © 2021 Elsevier Ltd
Development of a unified railway track stability management tool to enhance track safety
- Authors: Ahmad, Shah , Mandal, Nirmal , Chattopadhyay, Gopinath , Powell, John
- Date: 2013
- Type: Text , Journal article
- Relation: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit Vol. 227, no. 5 (2013), p. 493-516
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- Description: Track buckling is a serious problem for railways. High longitudinal rail stresses contribute to problems such as track buckling, rail joint failure, rail breakage and failure of turnouts. The direct and indirect costs of track buckling problems are very high. The influences of rail temperature, stress-free temperature (SFT) and lateral misalignment of track on track buckling need comprehensive investigation. In this paper, an experimental design comprising strain gauges, thermocouples and rail stress sensors has been implemented on the Queensland Rail heavy haul 60 kg/m rail network. A new creep measurement technique using internal rail stress has been developed. The changes in rail neutral temperature due to the variation of actual rail temperature and the occurrence of rail creep in straight and curved track is quantified. Modes of differences of SFT in the two rails at a location, and of SFT in straight track and in curved track are discussed. The relationship of SFT to rail temperature is also presented. Daily variation in rail temperature due to ambient air temperature is presented. Field trials showed that SFT can vary by 2-3 °C during the day. Based on this finding and the derivation of an equation for change of SFT, an improvement in utilising rail creep measurements for assessing track condition has resulted. This finding suggests that it is possible to determine the SFT throughout a day rather than just a single SFT value. This paper also presents a simple track stability management tool that is based on two major parameters, namely rail stress and track resistance. Each parameter in the tool has been given three levels of value to determine the required preventive measures. Overall, the tool decides the need for speed restriction during hot weather based on the quantified parameters from the field trials and rail standards. © IMechE 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.
Differential evolution algorithm for predicting blast induced ground vibrations
- Authors: Saadat, Mahdi , Hasanzade, Ali , Khandelwal, Manoj
- Date: 2015
- Type: Text , Journal article
- Relation: International Journal of Rock Mechanics and Mining Sciences Vol. 77, no. (2015), p. 97-104
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- Description: 1. Introduction One of the most crucial problems in construction blasting is to predict and then mitigate the ground vibration [1]. Blast-induced ground vibration is considered as one of the most important environmental hazards of mining operations and civil engineering projects. Intense vibration can cause critical damage to structures and plants nearby the open-pit mines, dams, and mine slopes, etc [2] and [3]. Researchers who deals with this undesirable phenomenon take into account various range of parameters in order to mitigate the detrimental effects of blasting. Blast influencing parameters can be divided into two categories [2]: (a) Uncontrollable parameters, such as geological and geotechnical characteristics of the rockmass. (b) Controllable parameters, such as burden, spacing, stemming, sub-drilling, delay time, etc.
Effect of negative excess pore-water pressure on the stability of excavated slopes
- Authors: Ghadrdan, Mohsen , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geotechnique Letters Vol. 10, no. 1 (Mar 2020), p. 20-29
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- Description: Generation of negative excess pore-water pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short- and long-term slope instability. The NEPWP generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Hence, total pore-water pressures immediately after excavation are lower than the ultimate equilibrium values, leading to a reduction of the average effective stresses in the slope and subsequently threatening stability in the long term. In this research study, the stability of three benchmark civil and mining excavations has been studied, considering the effects of the generation and dissipation of NEPWP. A series of numerical simulations are conducted to determine the role of in situ stresses and time in NEPWP dissipation as well as the consequent effects on the stability of the excavated slopes. To conduct a realistic time-dependent transient analysis, fully coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels lead to higher NEPWP generation and higher factor of safety values in the short term. Thereafter, the dissipation of NEPWP threatens the long-term stability of the excavation.
Elucidating the impact of micro-scale heterogeneous bacterial distribution on biodegradation
- Authors: Schmidt, Susanne , Kreft, Jan-Ulrich , Mackay, Rae , Picioreanu, Cristian , Thullner, Martin
- Date: 2018
- Type: Text , Journal article
- Relation: Advances in Water Resources Vol. 116, no. (2018), p. 67-76
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- Description: Groundwater microorganisms hardly ever cover the solid matrix uniformly–instead they form micro-scale colonies. To which extent such colony formation limits the bioavailability and biodegradation of a substrate is poorly understood. We used a high-resolution numerical model of a single pore channel inhabited by bacterial colonies to simulate the transport and biodegradation of organic substrates. These high-resolution 2D simulation results were compared to 1D simulations that were based on effective rate laws for bioavailability-limited biodegradation. We (i) quantified the observed bioavailability limitations and (ii) evaluated the applicability of previously established effective rate concepts if microorganisms are heterogeneously distributed. Effective bioavailability reductions of up to more than one order of magnitude were observed, showing that the micro-scale aggregation of bacterial cells into colonies can severely restrict the bioavailability of a substrate and reduce in situ degradation rates. Effective rate laws proved applicable for upscaling when using the introduced effective colony sizes.