ORCID Profile
0000-0001-7280-9472
Current Organisation
University of South Australia
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Trans Tech Publications, Ltd.
Date: 12-2012
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.629.433
Abstract: A stochastic analysis that incorporates spatial variability of material parameter of clay i.e. undrained shear strength, c within the finite element analysis was done. A smoother change of c between two neighbouring soil elements is expected than two elements at a distance apart, thus a spatial correlation length is used within the random field to describe the distance over which random values tend to be correlated. When the correlation lengths in horizontal and vertical directions are same, the soil elements can be described ‘isotropic’. Most of the previous studies investigated the effect of variation of c in terms of coefficient of variation, COV (standard deviation/mean) and the isotropic correlation length on bearing capacity. However, the correlation length of soil may not be isotropic as they may be deposited in layers i.e. correlation length in horizontal direction may be higher than that in vertical direction. Thus, this study investigated the effect of isotropic as well as anisotropic (in terms of correlation length) conditions and their lengths over a range of COV of c on the bearing capacity. The result of this study would help to understand the effect of soil anisotropy on bearing capacity.
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2018
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2021
Publisher: American Society of Civil Engineers
Date: 21-03-2019
Publisher: American Society of Civil Engineers
Date: 21-03-2019
Publisher: American Society of Civil Engineers
Date: 23-03-2023
Publisher: American Society of Civil Engineers
Date: 17-03-2015
Publisher: Springer International Publishing
Date: 11-2019
Publisher: Springer International Publishing
Date: 11-2019
Publisher: Springer International Publishing
Date: 28-10-2018
Publisher: Thomas Telford Ltd.
Date: 09-2021
Abstract: The discrete-element method (DEM) has gained popularity for developing a qualitative understanding of soil behaviour under a critical state soil mechanics (CSSM) framework. Most studies with a three-dimensional assembly of particles have used spheres as representative granular material to reduce computational demands. However, most granular materials – for ex le, sands – are not rounded, but possess features of angularity. Therefore, ellipsoid and cluster particles with different degrees of eccentricity were used in this study to evaluate the effect of the particle shape on the drained and undrained triaxial loading behaviour after isotropic and K 0 consolidation. The particle numerical properties and grain size distributions were kept the same for all specimens, irrespective of particle shape. The critical state data points for spheres and ellipsoids plotted on almost the same critical state line (CSL) in e–log(p′) space, whereas the CSLs of clusters plotted above them. Additionally, M lines shifted downward with increasing sphericity. It was also found that the stress ratio at the triggering of static liquefaction (η IS = q ′) in η IS –ψ space was affected by particle shape and consolidation path. The dilatancy (d = dε v p /dε q p ) was also affected by particle shape. It was found that dilatancy parameters for the SANISAND constitutive model are affected by particle shape, which may contribute to an improved understanding of particle shape in constitutive modelling.
Publisher: Thomas Telford Ltd.
Date: 05-2021
Abstract: The discrete-element method (DEM) was used to simulate constant-volume (undrained) triaxial compression tests for coarse particles (sand) mixed with non-plastic fines. Simulations were performed on granular mixtures with a range of fines contents (f c ) – namely, 0, 0·05, 0·10 and 0·20. The critical state and micromechanical responses of these mixtures were evaluated. The influence of f c on sand behaviour was captured when f c f thre , where f thre represents a threshold fines content, which corresponds to a transition from a fines-in-sand soil matrix to a sand-in-fines soil matrix. The DEM was utilised to assess the micromechanical participation of fines within the sand skeleton (matrix). Such evaluations led to assessing the performance of the equivalent granular void ratio (e*), the equivalent granular state parameter (ψ*) and ultimately their inherent parameter b, which represents the proportion of fines actively participating in the sand skeleton structure. It was observed that through capturing the stress partition of contact types within granular mixtures, a reasonable approximation of the active proportion of contacts within the sand matrix could be obtained. This led to a new DEM interpretation of the b parameter. The study therefore evaluated the concept and applicability of the equivalent state theory for sand–fines mixtures.
Publisher: Springer Singapore
Date: 2020
Publisher: Thomas Telford Ltd.
Date: 12-2018
Abstract: The characteristic features of undrained responses of granular materials, for ex le, stress ratio at instability ( η IS ) and phase transformation ( η PT ) states and the critical state (CS) behaviour, are often influenced by the consolidation history. However, there are limited studies in the literature, and a consensus has not yet been reached. This study combined the triaxial test of yellow silty sand and the three-dimensional discrete element method (DEM) simulation of ellipsoid particles under a triaxial condition to evaluate the effect of isotropic and K 0 consolidations. Triaxial test data formed non-unique CS lines (CSLs) in the e–log(p′) space for isotropic and K 0 tests, whereas the CSL was unique for DEM simulations where e and p′ are the void ratio and mean effective stress, respectively. The micromechanical quantities, coordination number (C N ) and fabric anisotropy (F vM ) at the CS, also showed a unique relation with p′. The characteristic features, η IS and η PT , showed good correlation with the state parameter (ψ ) and the density indices. It was found that the η IS decreased with ψ, and the correlation was dependent on consolidation type. The micromechanical analysis suggested that F vM is a better parameter than C N to characterise the macromechanical behaviour. This study unambiguously supports the applicability of CS theory and provides insights into micromechanics of granular materials.
Publisher: Thomas Telford Ltd.
Date: 02-2017
Abstract: The behaviour of granular material was investigated by simulating an undrained triaxial compression test for three-dimensional assembly of ellipsoid particles over a wide range of void ratio, e, and mean confining stress, p′. The assembly was either isotropically consolidated or K 0 consolidated prior to undrained shearing up to 30% axial strain to reach steady-state conditions. A unique steady-state line was obtained, irrespective of the consolidation path. The micro-mechanical quantities, such as coordination number and von Mises fabric in terms of second invariant of deviatoric fabric, F vM , also reached steady-state values. The normalised anisotropic fabric variable, A, and the trace of the joint stress–fabric tensor, K F , evolved during undrained simulation and reached the steady-state value at the end of shearing. This forms a unique relationship in K F –p′–e space and the projection of this relationship in e–log(p′) space is the classical steady-state line. This underpins the concept of fabric evolution and steady-state fabric in anisotropic critical state theory. The relationships of state parameter, ψ, and stress ratio at instability, η IS = (q ′) IS , were dependent on consolidation path, and the difference was not related to coordination number, but to F vM . However, a new phenomenon was observed that stress ratio, η, at the end of K 0 consolidation and η IS may reach beyond the steady-state stress ratio, M. Experimental data are needed to verify this until then such behaviour should be regarded as unproven.
Publisher: Springer Science and Business Media LLC
Date: 03-12-2022
Publisher: American Society of Civil Engineers
Date: 21-02-2020
Publisher: MDPI AG
Date: 17-10-2021
DOI: 10.3390/EN14206760
Abstract: Expansive soils go through significant volume changes due to seasonal moisture variations resulting in ground movements. The ground movement related problems are likely to worsen in the future due to climate change. It is important to understand and incorporate likely future changes in design to ensure the resilience of structures built on such soils. However, there has been a limited amount of work quantifying the effect of climate change on expansive soils movement and related behaviour of structures. The Thornthwaite Moisture Index (TMI) is one of the commonly used climate classifiers in quantifying the effect of atmospheric boundary on soil behaviour. Using the long-term weather data and predicted future changes under different emission scenarios, a series of TMI maps are developed for South Australia. Potential changes in ground movement are then estimated for a selected area using a simplified methodology where the effect of future climate is captured through changes in TMI. Results indicate that South Australia is likely to face a significant reduction in TMI under all emission scenarios considered in this study. The changes in TMI will lead to a considerable increase in potential ground movement which will influence the behaviour of structures built on them and in some areas may lead to premature failure if not considered in the design.
Publisher: MDPI AG
Date: 24-11-2022
DOI: 10.3390/SU142315662
Abstract: Lightweight structures built on expansive soils are susceptible to damage caused by soil movement. Financial losses resulting from the improper design of structures on expansive soils can be significant. The interactions and failure mechanisms of different geotechnical structures constructed on such soils differ depending on the structure type, site characteristics, and climatic conditions, as the behaviour of expansive soils is influenced by moisture variations. Therefore, the performance of different geotechnical structures (e.g., lightweight footings for residential buildings) is expected to be adversely affected by climate change (especially rainfall and temperature change), as geotechnical structures are often designed to have a service life of 50–100 years. Some structures may even fail if the effect of climate change is not considered in the present design. This review aims to provide insights into problems associated with expansive soils that trigger the failure of lightweight structures, including current investigations and industry practices. This review recognises that although the soil moisture conditions govern expansive soil behaviour, limited studies have incorporated the effect of future climate changes. In addition, this review identifies the need to improve the current Australian design practice for residential footings through the inclusion of more site-specific investigations and expected climate changes.
Publisher: American Society of Civil Engineers
Date: 17-03-2015
Publisher: American Society of Civil Engineers
Date: 17-03-2022
Publisher: Springer Singapore
Date: 2021
Publisher: MDPI AG
Date: 06-12-2022
DOI: 10.3390/GEOSCIENCES12120449
Abstract: Soil liquefaction or instability, one of the most catastrophic phenomena, has attracted significant research attention in recent years. The main cause of soil liquefaction or instability is the reduction in the effective stress in the soil due to the build-up of pore water pressure. Such a phenomenon has often been thought to be related to the undrained shearing of saturated or nearly saturated sandy soils. Notwithstanding, many researchers also reported soil instability under a drained condition due to the reduction in lateral stress. This condition is often referred to as the constant shear drained (CSD) condition, and it is not uncommon in nature, especially in a soil slope. Even though several catastrophic dam failures have been attributed to CSD failure, the failure mechanisms in CSD conditions are not well understood, e.g., how the volumetric strain or effective stress changes at the triggering of flow deformation. Researchers often consider the soil fabric to be one of the contributors to soil behaviour and use this parameter to explain the failure mechanism of soil. However, the soil fabric is difficult to measure in conventional laboratory tests. Due to that reason, a numerical approach capable of capturing the soil fabric, the discrete element method (DEM), is used to investigate the CSD shearing mechanism. A series of simulations on 3D assemblies of ellipsoid particles was conducted. The DEM specimens exhibited instability behaviour when the effective stress paths nearly reached the critical state line. It can be clearly observed that the axial and volumetric strains changed suddenly when the stress states were close to the critical state line. Alongside these micromechanical observations, the study also presents deeper insights into soil behaviour by relating the macro-observations to the micromechanical aspect of the soil.
Publisher: American Society of Civil Engineers (ASCE)
Date: 07-2023
Publisher: Elsevier BV
Date: 10-2021
Publisher: Thomas Telford Ltd.
Date: 13-09-2022
Publisher: CRC Press
Date: 04-09-2014
DOI: 10.1201/B17435-27
Publisher: Springer International Publishing
Date: 28-10-2018
Publisher: Frontiers Media SA
Date: 17-02-2023
DOI: 10.3389/FBUIL.2023.1117858
Abstract: Soil is a naturally heterogeneous material and can show significant spatial variation in strength and other properties. For silty and clayey soils, these variations are often more pronounced. Despite such variation, many past studies considered these soils as homogeneous and only considered a single set of soil parameters. This may lead to underestimation of the failure potential of geo-structure such as natural slopes, water retaining dams, retaining walls, etc. A finite element method considering soil variability should be an ideal tool to investigate the behaviour of these soils. This study adopted a 2D random finite element method to evaluate the effect of such variability on slope stability. The spatial variability was implemented by using the coefficient of variation ( COV ) and the spatial correlation length ( θ ) for cohesion. It was found that the soil slope with higher COV would have a higher chance of failure, whereas the soil slope with less COV might not show any failure. In addition, the soil with a higher θ , in general, show less potential of failure. In the literature, most studies considered an isotropic condition for the soil, i.e., θ in x and y directions are the same θ x = θ y , which is not realistic. Therefore, the soil anisotropy (i.e., θ x ≠ θ y ) was considered carefully in this study. It was found that the probability of failure for anisotropic soil might be significantly higher than the isotropic soil.
Publisher: Springer International Publishing
Date: 28-10-2018
Publisher: Springer Science and Business Media LLC
Date: 13-10-2020
Publisher: American Society of Civil Engineers
Date: 23-03-2023
Publisher: American Society of Civil Engineers
Date: 23-03-2023
No related grants have been discovered for Hoang Bao Khoi Nguyen.