A direct time-domain procedure for the seismic analysis of dam–foundation–reservoir systems using the scaled boundary finite element method
- Authors: Qu, Yanling , Chen, Denghong , Liu, Lei , Ooi, Ean Tat , Eisenträger, Sascha , Song, Chongmin
- Date: 2021
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 138, no. (2021), p.
- Full Text: false
- Reviewed:
- Description: In this paper, a direct time-domain procedure for the seismic analysis of dam–reservoir–foundation interactions is presented based on the scaled boundary finite element method (SBFEM). The SBFEM is a semi-analytical method and requires the discretization of boundary only. The geometric complexity in the bounded dam–reservoir–foundation system is easily handled in the SBFEM using quadtree meshes where each structural component can be discretized independently. The elastic wave fields in the unbounded foundation are rigorously captured through SBFE solutions in terms of displacement unit-impulse response functions, while the acoustic wave propagation in the semi-infinite reservoir is modelled by the SBFE-based doubly asymptotic open boundary. The input of seismic excitations is addressed by incorporating the Domain Reduction Method (DRM) into the SBFEM. Cracks are modelled efficiently and accurately by combining the SBFEM and quadtree meshes. The accuracy and efficiency of the proposed methodology is investigated by studying several benchmarks, Pine Flat dam and Jin'anqiao dam. © 2021 Elsevier Ltd
Assessing trust level of a driverless car using deep learning
- Authors: Karmakar, Gour , Chowdhury, Abdullahi , Das, Rajkumar , Kamruzzaman, Joarder , Islam, Syed
- Date: 2021
- Type: Text , Journal article
- Relation: IEEE Transactions on Intelligent Transportation Systems Vol. 22, no. 7 (2021), p. 4457-4466
- Full Text: false
- Reviewed:
- Description: The increasing adoption of driverless cars already providing a shift to move away from traditional transportation systems to automated ones in many industrial and commercial applications. Recent research has justified that driverless vehicles will considerably reduce traffic congestions, accidents, carbon emissions, and enhance the accessibility of driving to wider cross-section of people and lifestyle choices. However, at present, people's main concerns are about its privacy and security. Since traditional protocol layers based security mechanisms are not so effective for a distributed system, trust value-based security mechanisms, a type of pervasive security, are appearing as popular and promising techniques. A few statistical non-learning based models for measuring the trust level of a driverless are available in the current literature. These are not so effective because of not being able to capture the extremely distributed, dynamic, and complex nature of the traffic systems. To bridge this research gap, in this paper, for the first time, we propose two deep learning-based models that measure the trustworthiness of a driverless car and its major On-Board Unit (OBU) components. The second model also determines its OBU components that were breached during the driving operation. Results produced using real and simulated traffic data demonstrate that our proposed DNN based deep learning models outperform other machine learning models in assessing the trustworthiness of individual car as well as its OBU components. The average precision of detection accuracies for the car, LiDAR, camera, and radar are 0.99, 0.96, 0.81, and 0.83, respectively, which indicates the potential real-life application of our models in assessing the trust level of a driverless car. © 2000-2011 IEEE.
Detection and verification of tropical cyclones and depressions over the South Pacific Ocean basin using ERA-5 reanalysis dataset
- Authors: Yeasmin, Alea , Chand, Savin , Turville, Christopher , Sultanova, Nargiz
- Date: 2021
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 41, no. 11 (2021), p. 5318-5330
- Full Text: false
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- Description: Tropical cyclones (TCs) are one of the most destructive synoptic systems and can cause enormous loss of life and property damages in the South Pacific island nations. The impact of tropical depressions (TDs, i.e. weaker systems that do not develop into TCs) can also be staggering in the region in terms of heavy flooding and landslides, but a lack of complete records often hinders research involving TD impacts. A methodology has been developed here to detect TDs in the ERA-5 reanalysis dataset (the fifth generation ECMWF atmospheric reanalysis of the global climate) using the Okubo–Weiss–Zeta parameter (OWZP) detection scheme. The new South Pacific Enhanced Archive for Tropical Cyclones dataset (SPEArTC), the Dvorak analysis of satellite-based cloud patterns over the South Pacific Ocean basin, and a rainfall dataset for various stations and historical archives have been utilized to validate ERA5-derived TCs and TDs for the period between 1979 and 2019. Results indicate that the OWZP method shows substantial skill in capturing the realistic climatological distribution of TDs (as well as TCs) for the South Pacific Ocean in the ERA5 reanalysis, paving a way forward for future climatological studies involving the impacts of TCs and TDs over the island nations using longer-term reanalyses products such as the 20th-century reanalysis dataset that extends back to the 1850s. © 2021 Royal Meteorological Society
Failure analysis of articulated paddings at crossing interface between crossing cable and crossed pipeline
- Authors: Reda, Ahmed , Elgazzar, Mohamed , Sultan, Ibrahim , Shahin, Mohamed , McKee, Kristoffer
- Date: 2021
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 115, no. (2021), p.
- Full Text: false
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- Description: While subsea crossings are undesirable for many reasons, they are unavoidable due to the sheer density of subsea assets. The use of articulated paddings is a cost-effective and practical method to achieve the required vertical separation between the crossing and the crossed pipelines or cables, though, not without limitations. In this paper, the failure of articulated padding at several points along a subsea cable in operation was investigated. The articulated padding has experienced partial fractures at numerous crossing locations and in some places has fallen off the cable completely. A complete failure mode analysis was conducted where several possible modes of failure were considered in detail. In-place finite element (FE) analyses of the articulated padding components and the corresponding environment were also performed. The FE modelling concluded that the original design loads were significantly lower than the expected worst-case load scenarios. To replicate the failure mode, two abrasion tests were also conducted and the results of which were studied. It was concluded that the predominant failure mode (partial fracture to the articulated padding discs) was likely a combination of the increased dynamic loads, excessive lateral movement causing unexpected levels of fretting, unbalanced free span causing unexpected stress concentration factors and reduction in material mechanical properties. All above factors have contributed to the root cause of the system failure and instigated the predominant mode of failure “partial fracture”. © 2021
Improving expansive clay subgrades using recycled glass : resilient modulus characteristics and pavement performance
- Authors: Yaghoubi, Ehsan , Yaghoubi, Mohammadjavad , Guerrieri, Maurice , Sudarsanan, Nithin
- Date: 2021
- Type: Text , Journal article
- Relation: Construction and Building Materials Vol. 302, no. (2021), p.
- Full Text: false
- Reviewed:
- Description: The scarcity of sound soils, especially in urban areas, often forces engineers to construct the pavement on problematic subgrade soils such as expansive clays. The associated cost involved in replacing the existing problematic soil is avoided by adopting treatment techniques. In this study, a type of high plasticity expansive clay was mixed with 10, 20, and 30% sand-size recycled glass (RG) as a non-chemical soil treatment approach. An extensive investigation comprising experimental works, numerical modeling, and pavement performance analysis was undertaken. After determination of the physical properties of clay and RG, resilient modulus characteristics of clay and the three clay-RG mixtures were carried out through an experimental program. Subsequently, the obtained resilient modulus data sets were incorporated into a finite element analysis program in order to analyze the stress-strain response of pavement models founded on clay and RG-treated subgrades. The compressive and tensile strains achieved through the analysis of the pavement models under traffic loads were next used to compare each pavement model with respect to fatigue and rutting performances. The experimental results showed up to a 113% increase in resilient modulus of clay by the addition of 30% RG. The outcomes of the analysis on pavement systems modeled using the experimental input showed a considerable reduction in compressive and tensile strains by treating the clay subgrade with RG. Consequently, the strain reduction exhibited a significant increase in fatigue life and rutting life of pavements founded on RG treated clay subgrades. The outcomes of this research aim to encourage the construction industry to consider the utilization of environmentally clean recycled aggregates, such as RG, for improving subgrades with problematic soils and hence, promote sustainable construction materials and approaches. © 2021 Elsevier Ltd
Maximising the efficiency of Menard pressuremeter testing in cohesive materials by a cookie-cutter drilling technique
- Authors: Tolooiyan, Ali , Dyson, Ashley , Karami, Mojtaba , Shaghaghi, Tahereh , Ghadrdan, Mohsen , Tang, Zhan
- Date: 2021
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 287, no. (Jun 2021), p. 106096
- Full Text: false
- Reviewed:
- Description: Menard pressuremeter testing has been widely used in geotechnical engineering applications for 40 years and is an important technique in determining in-situ horizontal stress distributions. In this study, Menard pressuremeter testing is combined with a "cookie-cutter" insertion technique to determine horizontal stresses for a soft-rock in an operational Australian mine. The method presents an alternative to the Self-Bored Pressuremeter, with cookie-cutter drill rods allowing for sample recovery and further laboratory testing. The method accommodates for the presence of gravel and hard layered materials that present a risk of damage to cutting shoes of Self-Bored Pressuremeter devices. The combination of a sonic drill rig, coupled with the cookie cutter rods produces a close tolerance pocket resulting in "pseudo self boring pressuremeter tests". The undrained shear strength, unload-reload shear modulus and in-situ horizontal stress are presented from pressuremeter tests conducted in the region for the first time. The undrained shear strength was observed in the range of 0.47-0.57 MPa, the unload-reload shear modulus between 17.43 and 18.25 MPa, the lift-off pressure in the range of 0.35-0.61 MPa. The K-0 of coal was equal to 1, with interseam materials ranging from 2.1 to 3.5. Results of the cookie-cutter insertion method are compared with conventional drilling methods, with the cookie-cutter insertion test providing results in good agreement with both advanced triaxial laboratory tests and FEM numerical analysis. Cookie-cutter pressuremeter tests were conducted on cohesive soils at Australia's second-largest open-pit mine, with pressuremeter test results presented for Victorian brown coal for the first time.
Numerical study on the compression-bending response of grouted connections in offshore structures
- Authors: Chen, Tao , Fang, Qi , Zhang, Chihai , Li, Weichao , Xiao, Zhigang
- Date: 2021
- Type: Text , Journal article
- Relation: Journal of Constructional Steel Research Vol. 185, no. (2021), p.
- Full Text: false
- Reviewed:
- Description: Grouted connections (GCs) are widely used to link the substructures and towers for offshore wind turbines and transfer various loads from the turbine and tower to the substructure. Extremely complex stresses are developed in these composite connections formed with steel pipes and grout fillings. This paper presents a numerical study, using ABAQUS, on the mechanical response of GCs under axial compression coupled with bending. The effect of axial load ratio on the moment-rotation responses, contact stress between steel pipes and grout, as well as compositions of flexural capacity. Further study is conducted on the stress distribution in the grouted connection under axial compression coupled with bending, and the stress distribution was derived with python script. Analysis shows that, axial load ratio plays a non-negligible role and the distribution of contact stress differs from that recommended by current design guide. These should be considered with caution in industrial design. In addition, this paper also proposes a method to derive the contact stress from numerical model constructed with Abaqus. The results show that contact pressure and shear keys provide the main components for the flexural capacity and the sum of Mp and Mshear-keys accounts for about 75% of the total capacity. And the values of the non-uniform coefficient of shear keys ηsk are all larger than 0.75 which shows that the force distribution between shear keys is extremely uneven. The outputs of this paper provide a further understanding of the GCs subject axial compression coupled with bending. © 2021 Elsevier Ltd
Robust modelling of implicit interfaces by the scaled boundary finite element method
- Authors: Dsouza, Shaima , Pramod, A. L. N. , Ooi, Ean Tat , Song, Chongming , Natarajan, Sundararajan
- Date: 2021
- Type: Text , Journal article
- Relation: Engineering Analysis with Boundary Elements Vol. 124, no. (2021), p. 266-286
- Full Text: false
- Reviewed:
- Description: In this paper, we propose a robust framework based on the scaled boundary finite element method to model implicit interfaces in two-dimensional differential equations in nonhomegeneous media. The salient features of the proposed work are: (a) interfaces can be implicitly defined and need not conform to the background mesh; (b) Dirichlet boundary conditions can be imposed directly along the interface; (c) does not require special numerical integration technique to compute the bilinear and the linear forms and (d) can work with an efficient local mesh refinement using hierarchical background meshes. Numerical examples involving straight interface, circular interface and moving interface problems are solved to validate the proposed technique. Further, the presented technique is compared with conforming finite element method in terms of accuracy and convergence. From the numerical studies, it is seen that the proposed framework yields solutions whose error is O(h2) in L2 norm and O(h) in the H1 semi-norm. Further the condition number increases with the mesh size similar to the FEM. © 2021 Elsevier Ltd
Slope stability analysis using deterministic and probabilistic approaches for poorly defined stratigraphies
- Authors: Ghadrdan, Moshen , Dyson, Ashley , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2021
- Type: Text , Journal article
- Relation: Geomechanics and Geophysics for Geo-Energy and Geo-Resources Vol. 7, no. 1 (2021), p.
- Full Text: false
- Reviewed:
- Description: The stability of slopes directly affects human lives, the environment, and the economy. Inaccurate geological profiles within numerical slope stability models can lead to potentially catastrophic consequences when model conditions do not appropriately reflect real-life stratigraphy. In cases where localised deposits are prevalent, probabilistic methods are often necessary to accommodate for unknown or poorly defined stratigraphies. Currently, there are no commercial geotechnical software packages that simulate probabilistic constitutive behaviour of materials within finite element methods for large-scale stratigraphic analysis. Instead, commercially available probabilistic methods such as the random limit equilibrium method are incapable of incorporating non-linear constitutive soil behaviour. For this reason, advanced constitutive models are seldom coupled with probabilistically varying soil layers or spatially variable soil parameters. The objective of this research is the implementation of a simplified method for probabilistic stratigraphic analysis within a commercially available FE environment, providing a technique to assess the effects of stratigraphic uncertainty on slope stability. The proposed method is presented, highlighting the impact of localised thin layers of soft material as well as their frequency and location on the slope of an operational open-pit mine. The significance of these stratigraphic effects is presented through a case study of Australia’s second-largest open-pit mine, at which the stability of a collapsed coal slope is analysed. To improve the reliability of the finite element method for slope stability assessment, the Monte Carlo approach has been incorporated to consider varying shear strength distributions for models incorporating advanced constitutive behaviour. Thicker probabilistically generated deposits of silty material resulted in increased slope Factors of Safety. Similarly, greater proportions of silty deposits within a predominantly clayey interseam produced larger safety factors than slopes without localised thin silty layers. Stratigraphic analysis indicated that the Factor of Safety was most sensitive to localised silt layers at depths greater than 83 m below ground level. © 2020, Springer Nature Switzerland AG.
SPEED: A deep learning assisted privacy-preserved framework for intelligent transportation systems
- Authors: Usman, Muhammad , Jan, Mian , Jolfaei, Alireza
- Date: 2021
- Type: Text , Journal article
- Relation: IEEE Transactions on Intelligent Transportation Systems Vol. 22, no. 7 (2021), p. 4376-4384
- Full Text: false
- Reviewed:
- Description: Roadside cameras in an Intelligent Transportation System (ITS) are used for various purposes, e.g., monitoring the speed of vehicles, violations of laws, and detection of suspicious activities in parking lots, streets, and side roads. These cameras generate big multimedia data, and as a result, the ITS faces challenges like data management, redundancy, and privacy breaching in end-to-end communication. To solve these challenges, we propose a framework, called SPEED, based on a multi-level edge computing architecture and machine learning algorithms. In this framework, data captured by end-devices, e.g., smart cameras, is distributed among multiple Level-One Edge Devices (LOEDs) to deal with data management issue and minimize packet drop due to buffer overflowing on end-devices and LOEDs. The data is forwarded from LOEDs to Level-Two Edge Devices (LTEDs) in a compressed sensed format. The LTEDs use an online Least-Squares Support-Vector Machines (LS-SVMs) model to determine distribution characteristics and index values of compressed sensed data to preserve its privacy during transmission between LTEDs and High-Level Edge Devices (HLEDs). The HLEDs estimate the redundancy in forwarded data using a deep learning architecture, i.e., a Convolutional Neural Network (CNN). The CNN is used to detect the presence of moving objects in the forwarded data. If a movement is detected, the data is forwarded to cloud servers for further analysis otherwise discarded. Experimental results show that the use of a multi-level edge computing architecture helps in managing the generated data. The machine learning algorithms help in addressing issues like data redundancy and privacy-preserving in end-to-end communication. © 2000-2011 IEEE.
Temperature and duration impact on the strength development of geopolymerized granulated blast furnace slag for usage as a construction material
- Authors: Arulrajah, Arul , Maghool, Farshid , Yaghoubi, Mohammadjavad , Phetchuay, Chayakrit , Horpibulsuk, Suksun
- Date: 2021
- Type: Text , Journal article
- Relation: Journal of Materials in Civil Engineering Vol. 33, no. 2 (2021), p.
- Full Text: false
- Reviewed:
- Description: Through the process of extracting iron from iron ore, a by-product is generated known as granulated blast furnace slag (GBFS). Traditional stabilization methods such as cement stabilization are not entirely sustainable options. This research investigates the engineering properties of geopolymer-stabilized GBFS and their viability for usage as a construction material. A combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used as the liquid alkaline activator (L) along with low-carbon pozzolanic binders, namely, fly ash (FA) and slag (S). The L was prepared with a Na2SiO3:NaOH ratio of 70 30 and binders were added up to 30%. The effect of different curing regimes on the strength of geopolymerized GBFS was evaluated using scanning electron microscopy (SEM) and unconfined compressive strength (UCS) tests. The effect of both the temperature and duration of curing had a vital role in the strength development of the mixtures. The test results indicated that the combination of FA+S as a geopolymer binder could perform better than FA or S alone. With the lowest UCS value of 7.8 MPa and highest value of 43 MPa, all the geopolymer-stabilized GBFS were found to be suitable for a variety of civil and construction applications. © 2020 American Society of Civil Engineers.
The effects of initial static deviatoric stress on liquefaction and pre-failure deformation characteristics of saturated sand under cyclic loading
- Authors: Liu, Zhiyong , Qian, Jiangu , Yaghoubi, Mohammadjavad , Xue, Jianfeng
- Date: 2021
- Type: Text , Journal article
- Relation: Soil Dynamics and Earthquake Engineering Vol. 149, no. (2021), p.
- Full Text: false
- Reviewed:
- Description: Initial static deviatoric stress can affect the liquefaction behaviour and deformation characteristics of saturated sand under cyclic loading. A series of cyclic triaxial tests were performed on a saturated sand consolidated under a constant vertical stress but different lateral stresses. The dependence of failure mechanism, liquefaction resistance, and stiffness evolution of the sand on initial static deviatoric stress ratio was investigated on medium dense to dense sand samples (Dr = 0.44 to 0.82). The pre-failure deformation and the direction of strain accumulation were analysed under different static deviatoric stress ratios. The results indicate that under cyclic loading with stress reversal condition, the effective mean stress in the samples could reduce to zero, which leads to cyclic mobility failure and completely loss of stiffness due to liquefaction. The stress state after cyclic loading could be above critical state line. Under non reversal loading condition, however, the effective mean stress cannot reduce to zero and therefore the samples fail under shear due to large strain accumulation. In this condition, the stress state at the end of the cyclic loading is approximately at the critical state line and hardly affected by initial deviatoric stress. The failure resistance of medium dense to dense sand is not greatly affected by initial static deviatoric stress until it is large enough to meet non-reverse loading condition. The ratio of axial stain to excess pore water pressure accumulation (or Δϵacc a/Δϵacc v) increases with the average static deviatoric stress ratio ηav. The strain accumulation direction roughly follows the flow rule of Modified Cam Clay model, independent of relative density and failure mechanism. © 2021 Elsevier Ltd
A dual scaled boundary finite element formulation over arbitrary faceted star convex polyhedra
- Authors: Ooi, Ean Tat , Saputra, Albert , Natarajan, Sundararajan , Ooi, Ean Hin , Song, Chongmin
- Date: 2020
- Type: Text , Journal article
- Relation: Computational Mechanics Vol. 66, no. 1 (2020), p. 27-47
- Full Text: false
- Reviewed:
- Description: A novel technique to formulate arbritrary faceted polyhedral elements in three-dimensions is presented. The formulation is applicable for arbitrary faceted polyhedra, provided that a scaling requirement is satisfied and the polyhedron facets are planar. A triangulation process can be applied to non-planar facets to generate an admissible geometry. The formulation adopts two separate scaled boundary coordinate systems with respect to: (i) a scaling centre located within a polyhedron and; (ii) a scaling centre on a polyhedron’s facets. The polyhedron geometry is scaled with respect to both the scaling centres. Polygonal shape functions are derived using the scaled boundary finite element method on the polyhedron facets. The stiffness matrix of a polyhedron is obtained semi-analytically. Numerical integration is required only for the line elements that discretise the polyhedron boundaries. The new formulation passes the patch test. Application of the new formulation in computational solid mechanics is demonstrated using a few numerical benchmarks. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
An investigation of cross-sectional spatial variation with random finite element method slope stability analysis
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geotechnical and Geological Engineering Vol. 38, no. 6 (2020), p. 6467-6485
- Full Text: false
- Reviewed:
- Description: The selection of two-dimensional cross-sections for plane-strain slope stability analysis often requires a range of assumptions such that the most appropriate cross-section is considered. When faced with complex strata, surface topologies and pore-water pressure distributions, the selection of an appropriate cross-section is non-trivial. Circumstances are further complicated when considering spatially variable soils and heterogeneous strength parameters. In this study, the effects of spatially variable geotechnical parameters are examined for a range of two-dimensional random finite element method (RFEM) simulations of an open-pit mine. A distinct set of random field instances are provided to each cross-section to isolate the impact of geometry and strata variation when coupled with spatially variable soil characterisations. Particular attention is given to the regions providing the greatest impact on factors of safety and representative slip surfaces for each slope geometry, evaluating the need for full three-dimensional RFEM simulation. Further statistical analyses are conducted to establish which random field slope stability cross-sections are significantly different from the underlying cross-section population, thereby identifying the best cross-section to represent the overall slope geometry. © 2020, Springer Nature Switzerland AG.
Investigation of an Australian soft rock permeability variation
- Authors: Tolooiyan, Ali , Dyson, Ashley , Karami, Mojtaba , Shaghaghi, Tahereh , Ghadrdan, Mohsen
- Date: 2020
- Type: Text , Journal article
- Relation: Bulletin of Engineering Geology and the Environment Vol. 79, no. 6 (2020), p. 3087-3104
- Full Text: false
- Reviewed:
- Description: In this study, permeabilities of Victorian Brown Coal (VBC) as an Australian soft rock are determined for a range of depths of a continuous coal seam located at the batter crest of the Yallourn brown coal open-cut mine in Victoria, Australia, by implementing a Lugeon packer testing procedure. Permeability values are determined both analytically and by numerical simulation and are compared with laboratory test results. Field testing resulted in permeabilities several orders of magnitude higher than laboratory testing, suggesting the existence of fractures common to lignite structures on a greater scale than can be observed in the laboratory. The variation of depth-based field and laboratory permeabilities is discussed, as well as the necessary conditions required for the numerical modelling of packer testing within VBC. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
- Description: Department of Economic Development, Jobs, Transport and Resources, DSDBI The second and third authors are funded by the Australian Government Research Training Program (RTP) and the GHERG scholarship programme.
Mitigation of desiccation cracks in clay using fibre and enzyme
- Authors: Xie, Yuekai , Costa, Susanga , Zhou, Limin , Kandra, Harpreet
- Date: 2020
- Type: Text , Journal article
- Relation: Bulletin of Engineering Geology and the Environment Vol. 79, no. 8 (2020), p. 4429-4440
- Full Text: false
- Reviewed:
- Description: Formation of cracks during desiccation is a natural phenomenon in expansive clay. Mitigation of desiccation-induced cracks is highly beneficial for increasing the life span of geo-infrastructures particularly in hydraulic barriers. Improvement of soil properties using additives is a key method in controlling desiccation crack formation and their influence. This paper presents experimental results for an expansive clay modified with nylon fibre and an enzyme-based product. A series of desiccation cracking tests were carried out with varying fibre contents and a constant enzyme dosage. Three-point bending beam tests were performed to evaluate tensile strength of the modified clay. The additives, fibre and the enzyme were able to alter the crack patterns significantly thereby alleviating the effects of cracks. Furthermore, the addition of enzyme alone increased the tensile strength by about 50% while the combined effect of both fibre and enzyme increased the tensile strength by approximately 100% compared with untreated soil. Based on measurement of crack patterns and other properties of the modified clay, the investigation suggests the potential for the fibre-enzyme addition to mitigate desiccation cracks. Further work needs to be carried out to determine optimal dosing requirements for each additive and investigate the effects of potential interactions between the fibre and enzyme. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Sensitivity of the stability assessment of a deep excavation to the material characterisations and analysis methods
- Authors: Ghadrdan, Mohsen , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geomechanics and Geophysics for Geo-Energy and Geo-Resources Vol. 6, no. 4 (2020), p.
- Full Text: false
- Reviewed:
- Description: Due to the spatial variability of material characterisations in deep and large scale excavations, stability assessment is often a challenging task. Numerous slope stability analysis methods based on a range of assumptions and principles are implemented in commercial software packages to ease the process of stability assessment of non-homogeneous and multi-layered slopes. However, the selection of a suitable method remains crucial as the application of an unrealistic or unsuitable method may lead to catastrophic consequences. Besides material shear strength parameters, and analysis methods, non-strength characterisations such as permeability and creep can affect the result of slope stability analysis significantly. In this study, the sensitivity of the stability assessment of a deep excavation in Australia to material characterisations such as friction angle, cohesion and permeability and creep is investigated by the use of different formulations and assumptions of the Limit Equilibrium Method (LEM) and the Finite Element Method (FEM) as the two most common slope stability methods. The results show that the stability assessment is highly sensitive to the applied method and assumptions. Moreover, the role of material strength and non-strength parameters and the selection of a suitable constitutive model in slope stability assessment is presented. © 2020, Springer Nature Switzerland AG.
Application of ground penetrating radar (GPR) to detect joints in organic soft rock
- Authors: Tolooiyan, Ali , Dyson, Ashley , Karami, Mojtaba , Shaghaghi, Tahereh , Ghadrdan, Mohsen
- Date: 2019
- Type: Text , Journal article
- Relation: Geotechnical Testing Journal Vol. 42, no. 2 (2019), p.
- Full Text: false
- Reviewed:
- Description: The detection of joints and discontinuities is of particular importance to the stability of a broad range of geostructures, including slopes and underground and open-pit mines. As a common example, the mechanical response of soft rocks observed within open-pit mines is significantly influenced by the existence of joint networks, resulting in a complex stress distribution that governs the stability factor of safety as well as the failure mechanism. In this article, surface geophysics scanning by ground penetrating radar (GPR) is presented for the detection of vertical joints at one of the largest open-pit coal mines in Australia. The optimum soil velocity, point interval, and antenna frequency for joint detection in Victorian Brown Coal (VBC) are presented in comparison with electromagnetic properties of known organic soils. Furthermore, the performance of an assorted set of post-processing signal filtering techniques to successfully identify the underground coal fractures are detailed, along with obstructions affecting the feasibility of GPR vertical joint discovery in this light organic soft rock.
Pipeline slug flow dynamic load characterization
- Authors: Reda, Ahmed , Forbes, Gareth , Sultan, Ibrahim , Howard, Ian
- Date: 2019
- Type: Text , Journal article
- Relation: Journal of Offshore Mechanics and Arctic Engineering Vol. 141, no. 1 (2019), p. 1-8
- Full Text: false
- Reviewed:
- Description: Flow of gas in pipelines is subject to thermodynamic conditions which produces twophase bulks (i.e., slugs) within the axial pipeline flow. These moving slugs apply a moving load on the free spanning pipe sections, which consequently undergo variable bending stresses, and flexural deflections. Both the maximum pipeline stress and deflection due to the slug flow loads need to be understood in the design of pipeline spans. However, calculation of a moving mass on a free spanning pipeline is not trivial and the required mathematical model is burdensome for general pipeline design engineering. The work in this paper is intended to investigate the conditions under which simplified analysis would produce a safe pipeline design which can be used by practicing pipeline design engineers. The simulated finite element models presented here prove that replacing the moving mass of the slug by a moving force will produce adequately accurate results at low speeds where the mass of the slug is much smaller than the mass of the pipe section. This result is significant, as the assumption of point load simplifies the analysis to a considerable extent. Since most applications fall within the speed and mass ratio which justify employing this simplified analysis, the work presented here offers a powerful design tool to estimate fatigue stresses and lateral deflections without the need of expensive timeconsuming inputs from specialized practitioners.
Prediction and classification for finite element slope stability analysis by random field comparison
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2019
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 109, no. (2019), p. 117-129
- Full Text: false
- Reviewed:
- Description: This paper considers probabilistic slope stability analysis using the Random Finite Element Method (RFEM) combined with processes to determine the level of similarity between random fields. A procedure is introduced to predict the Factor of Safety (FoS) of individual Monte Carlo Method (MCM) random field instances prior to finite element simulation, based on random field similarity measures. Previous studies of probabilistic slope stability analysis have required numerous MCM instances to reach FoS convergence. However, the methods provided in this research drastically reduce computational processing time, allowing simulations previously considered too computationally expensive for MCM analysis to be simulated without obstacle. In addition to computational efficiency, the comparison based procedure is combined with cluster analysis methods to locate random field characteristics contributing to slope failure. Comparison measures are presented for slope geometries of an Australian open pit mine to consider the impacts of associated factors such as groundwater on random field similarity predictors, while highlighting the capacity of the similarity procedure for prediction, classification and computational efficiency.