List of Titles

Numerical and finite element analysis of heat transfer in a closed loop geothermal system

- Hemmingway, Phil, Tolooiyan, Ali

Authors: Hemmingway, Phil , Tolooiyan, Ali
Date: 2014
Type: Text , Journal article
Relation: International Journal of Green Energy Vol. 11, no. 2 (2014), p. 206-223
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Description: Analysis of the thermal regime created by a geothermal borehole heat exchanger is performed using a closed form radial heat flow equation, a geothermal borehole heat exchanger design tool, and a finite-element model. Climatic, heat exchanger construction, and building load data are entered into the heat exchanger design tool to create a theoretical model along with thermal parameters from a number of geological formations. Output data from the design tool model are used in conjunction with the closed form radial heat flow equation to calculate the predicted temperature with respect to time and distance from the heat exchanger for the modeled ground formations. The output data from the design tool are also used to create a number of finite-element method models against which the predictions calculated using the closed form radial heat flow equation can be compared. A good correlation between the temperatures predicted by the finite-element models and the closed form equation calculations is observed. However, when used within its recommended limiting conditions, the closed form equation is shown to slightly underestimate the temperature of the ground when compared with the finite-element model predictions. The limiting conditions associated with the closed form equation are discussed in the context of the output from the finite-element method models.

Structural behaviour of an Australian silty clay (Coode Island silt) stabilised by treatment with slag lime

- Falah, Mahroo, Ranjbar Pouya, Kaveh, Tolooiyan, Ali, Mackenzie, Kenneth

Authors: Falah, Mahroo , Ranjbar Pouya, Kaveh , Tolooiyan, Ali , Mackenzie, Kenneth
Date: 2018
Type: Text , Journal article
Relation: Applied Clay Science Vol. 157, no. (2018), p. 198-203
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Description: A microstructural study of Coode Island Silt (CIS), a soft silty clay from the Melbourne area of Australia, stabilised with slag lime is reported. Slag lime is a blend of 80–85 wt% slag, 15 wt% hydrated lime, Ca(OH)2 and 3–8 wt% gypsum CaSO4.2H2O, and is typically used for soil stabilisation in roading applications. The morphologies of several homogeneous mixtures of slag lime and CIS were studied by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), which indicated the formation of the cementitious phases calcium carbonate, calcium silicate hydrate, calcium aluminium silicate hydrate, and calcium aluminium silicate carbonate. The progress of the CIS-slag lime reactions was also investigated by pH measurements. Slag lime was found to very actively promote pozzolanic reactions with CIS, shown by SEM to form crystalline reticular calcium silicate hydrate and other cementitious products. The most effective pozzolanic reactions occurred in a composite containing 12.5 wt% slag lime with CIS and contained the cement mineral ettringite, contributing to its high strength. These composites constitute a new class of materials with excellent potential for construction applications.

Performance of a geogrid reinforced soil wall on PVD drained multilayer soft soils

- Chen, Jianfeng, Tolooiyan, Ali, Xue, Jianfeng, Shi, Zhenming

Authors: Chen, Jianfeng , Tolooiyan, Ali , Xue, Jianfeng , Shi, Zhenming
Date: 2016
Type: Text , Journal article
Relation: Geotextiles and Geomembranes Vol. 44, no. 3 (2016), p. 219-229
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Description: A geogrid reinforced soil wall was built on Prefabricated Vertical Drain (PVD) improved multilayer soft soils at the end of a road embankment in Shanghai, China. One day after the last loading stage, an arc shaped settlement was observed on the embankment surface with little observable cracks on the side slopes, and sudden increase of pore water pressure was observed in the piezometers installed in the PVD improved zone. A three dimensional finite element analysis was carried out to compare the performance of the wall with PVDs functional and dysfunctional. The comparison supported the assumption that the PVDs may have failed during construction due to bending or kinking of PVDs caused by the large settlement and lateral movement in the ground. The analysis showed that the movement of the wall toe is very sensitive to its location in the cross direction. Therefore attention should be paid while using toe movement as an indication of wall stability. It shows that the failure had mainly taken place in between the shoulders of the embankment rather than the whole wall. For a full slide to develop, pull out or tensile failure may occur in the reinforcements on the side slopes. Large stresses can be generated in the geogrids in the cross embankment direction due to the uneven settlement observed in the ground. Considering this, biaxial geogrid should be considered if the stress is too high and the inclusion of wrap around geogrids on the side slopes may help to increase the integrity and stability of the wall. © 2015 Elsevier Ltd.

Optimisation of strength reduction finite element method codes for slope stability analysis

- Dyson, Ashley, Tolooiyan, Ali

Authors: Dyson, Ashley , Tolooiyan, Ali
Date: 2018
Type: Text , Journal article
Relation: Innovative Infrastructure Solutions Vol. 3, no. 1 (2018), p. 1-12
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Description: One of the modern methods for estimating the factor of safety for the stability of slopes is the strength reduction method. In recent times, computer codes have utilised the strength reduction method in conjunction with finite element analysis. This paper explores the implementation of a strength reduction finite element method with FORTRAN and Python codes in conjunction with the computer-aided engineering package Abaqus, incorporating a modified strength reduction definition, allowing for a refinement of the factor of safety search space. The computational efficiency of the modified method is compared with the traditional technique, for both 2D and 3D analysis. The algorithm results are compared for contrasting FEM element types and geometries and benchmarked against proprietary geotechnical finite element solvers.

Characterisation of permanent deformation behaviour of unbound granular materials using repeated load triaxial testing

- Zhalehjoo, Negin, Tolooiyan, Ali, Mackay, Rae, Bodin, Didier

Authors: Zhalehjoo, Negin , Tolooiyan, Ali , Mackay, Rae , Bodin, Didier
Date: 2018
Type: Text , Conference proceedings
Relation: 10th International Conference on the Bearing Capacity of Roads, Railways and Airfields, BCRRA 2017; Athens, Greece; 28th-30th June 2017; published in Bearing Capacity of Roads, Railways and Airfields p. 159-166
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Description: Unbound Granular Material (UGM) used in the base/subbase layers of a flexible pavement structure constitutes the vast majority of the material found in roads around the world. The permanent deformation of a compacted UGM layer due to cyclic deviatoric loading has a significant effect on the performance of the pavement structure. The accurate prediction of the magnitude of accumulated permanent strain at varying load cycles and stress levels plays an important role in improving the design and maintenance of flexible pavements. In this study, samples of two road base UGMs are tested to evaluate the characteristics of permanent deformation using the laboratory Repeated Load Triaxial (RLT) test. Three permanent deformation models are used to predict the magnitude of strain accumulation of the studied UGMs. The permanent strain results predicted by the models are compared against those measured by laboratory RLT tests to evaluate the prediction ability of each model.
Description: Bearing Capacity of Roads, Railways and Airfields - Proceedings of the 10th International Conference on the Bearing Capacity of Roads, Railways and Airfields, BCRRA 2017

Post-long-term cyclic behaviour of Coode Island Silt (CIS) containing different sand content

- Jamali, Hassan, Tolooiyan, Ali, Dehghani, Masoud, Asakereh, Adel, Kalantari, Behzad

Authors: Jamali, Hassan , Tolooiyan, Ali , Dehghani, Masoud , Asakereh, Adel , Kalantari, Behzad
Date: 2018
Type: Text , Journal article
Relation: Applied Ocean Research Vol. 80, no. (2018), p. 11-23
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Description: It is widely accepted that the post-cyclic stiffness and shear strength of marine clays may alter as a consequence of experiencing a large number of deviatoric load cycles. Most marine clays in bay areas are already undergoing long-term one-way and low amplitude ocean and wind waves either because of the seabed topography or existing infrastructures. For the engineering of such clays, particular attention should be given to the post-cyclic behaviour of the material when investigating the effect of alteration in loading regimes exerted by human-made or natural phenomena such installation of new infrastructure, earthquake, tsunami and port upgrade construction, in which the magnitude of the applied load changes. As one of the most sensitive soft soils in Melbourne, Coode Island Silt (CIS) at the northern shoreline of Port Phillip Bay comprises a considerable and variable amount of sand. This paper explores the post-cyclic constitutive behaviour of CIS containing variable sand content. To investigate the stiffness and shear strength of CIS subsequent to experiencing a large number of low amplitude cycles, a series of post-cyclic triaxial tests are performed on CIS specimens with varying sand content ratio up to 30%, immediately after applying 30,000 semi-sinusoidal load cycles. Based on the test results, it is found that the undrained shear strength of CIS, does not alter considerably as the results of long-term cyclic loading. However, a significant increase in the secant stiffness of CIS followed by very brittle yielding is observed. In the end, it is intended that results be summarised in a form applicable by industry. Hence, the possible effects of such alterations in the constitutive behaviour of CIS on the design of monopile foundations are discussed.

Application of ground penetrating radar (GPR) to detect joints in organic soft rock

- Tolooiyan, Ali, Dyson, Ashley, Karami, Mojtaba, Shaghaghi, Tahereh, Ghadrdan, Mohsen

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.
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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.

Understanding deep aquifer responses to interseam materials of brown coal mines

- Rastogi, Sid, Barton, Andrew, Mackay, Rae, Kandra, Harpreet, Tolooiyan, Ali

Authors: Rastogi, Sid , Barton, Andrew , Mackay, Rae , Kandra, Harpreet , Tolooiyan, Ali
Date: 2018
Type: Text , Conference proceedings , Conference Paper
Relation: 2018 Hydrology and Water Resources Symposium: Water and Communities, HWRS 2018; Melbourne, Australia; 3rd-6th December 2018 p. 711-722
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Description: Brown coal deposits in the Latrobe Valley form part of the tertiary coal system of the Gippsland Basin, which is one of three major tertiary basins in Victoria, Australia. There are currently two operating brown coal mines in the Latrobe Valley (Yallourn and Loy Yang Mines) where coal is mined for power generation, with a third mine (Hazelwood) having recently ceased operations. An ongoing challenge in the mines is the management of geotechnical stability of the open pit batters. This includes the management of significant issues such as instability due to floor heave which is directly related to groundwater pressures of the underlying confined aquifers. The time dependent pressure distributions in the interseam layers are complex due to the complex heterogeneous stratigraphy of these layers. A model of the fine scale stratigraphy using Minescape has been developed to explore how pressure redistribution occurs and how the groundwater flow systems impact the interseam pore pressures due to pumping activity, leading to potential impacts on the mine batter movements. The objective of the preliminary groundwater modelling presented in this paper is to examine the hydraulic connectivity between the lower pumped aquifer layers and the upper sandy layers. The goal is to assess whether the connections are solely through vertical flows through the interbedded aquitard layers or whether there are lateral connections of the sandy layers that govern the vertical connections. A one-dimensional vertical flow model has been used for this purpose in conjunction with high quality groundwater head data from multiple depths in vertically sealed bores. The results suggest that the pressure redistributions vertically cannot be explained by vertical flows alone and that lateral exchange between layers is also occurring. This work will inform the next stage of modelling that will use the detailed stratigraphic modelling in three dimensions.

Probabilistic investigation of RFEM topologies for slope stability analysis

- Dyson, Ashley, Tolooiyan, Ali

Authors: Dyson, Ashley , Tolooiyan, Ali
Date: 2019
Type: Text , Journal article
Relation: Computers and Geotechnics Vol. 114, no. (2019), p. 1-15
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Description: The Random Finite Element Method (RFEM) is an increasingly popular tool in geotechnical engineering, especially for analysis of spatial variation and uncertainty in slope stability. Although the method has gained prominence in recent years, topological effects of strong and weak zones and the impact of their locations remain largely unknown. Although numerous potential slip surface realisations can be generated with RFEM, probabilistic failure statistics are often governed by several representative slip surfaces (RSS). In this research, random field similarity methods and clustering techniques are coupled with RFEM slope stability simulation to determine the impact of shear strength spatial patterns on slope failure mechanisms and safety factors. Regions of significance are highlighted within a case study of a Victorian open-cutbrown coal mine, with particular attention given to the effects on the slope failure surface as well the factor of safety. Results are presented of Factor of Safety distributions when particular slip surfaces and clustering constraints are imposed, providing further understanding of the impacts of shear strength characteristics on probabilistic simulation results.

Prediction and classification for finite element slope stability analysis by random field comparison

- Dyson, Ashley, Tolooiyan, Ali

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
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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.

Unconfined Expansion Test (UET) for measuring the tensile strength of organic soft rock

- Tang, Zhan, Tolooiyan, Ali, Mackay, Rae

Authors: Tang, Zhan , Tolooiyan, Ali , Mackay, Rae
Date: 2017
Type: Text , Journal article
Relation: Computers and Geotechnics Vol. 82, no. (2017), p. 54-66
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Description: An Unconfined Expansion Test (UET) is presented for measuring the tensile strength of Intermediate Geotechnical Materials (IGM). The test is performed by generating radial cavity expansion inside a cylindrical specimen. Pressure redistributes evenly around the cavity wall during the test. Tensile failure initiates on the weakest plane around the cavity and radially propagates across the specimen. By also capturing the stress-strain relationship and deriving the shear modulus, a UET is also capable of measuring the tensile elastic modulus of the material. An eXtended Finite Element Method (XFEM) analysis using Abaqus/Standard has been carried out to verify the UET test results. © 2016 Elsevier Ltd

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