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Lookup NU author(s): Professor Mohamed Rouainia, Dr Sadegh NadimiORCiD
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Inter-granular bonds are a significant aspect to understand the mechanical behaviour of cemented sands, sandstones, methane hydrate sediments, concrete, asphalt, etc. In particular, softening due to de-bonding, insensitivity of the small strain stiffness to stress, as well as the dependence of failure mode on confining stress have been attributed to the presence of cement between individual particles. To this extent, the contribution of numerical simulations using the Discrete Element Method (DEM) has been important. At the core of these DEM simulations are the contact models required to replicate the particle-scale interactions that underlie the observed macro-scale behaviour of cemented soils. Some of the most sophisticated contact models simulate inter-granular bond cement behaviour by calculating inter-particle forces at cemented contacts. Curve-fitting to experimental results are frequently used to derive expressions for the normal and shear stress within the cement. Other approaches consider elastic beam methods or relatively simple elasto-plastic models, which incorporate tensile strength at inter-particle contacts due to the presence of cement. Whilst analytically derived contact models incorporate the dependence of bond size and shape, they still share with most of the common models the limitation of using circular/spherical individual particles of equal size. In addition, the same macro-scale response can be obtained with completely different input parameters. Furthermore, a common feature is that the inter-granular cement bond can only exist between two individual particles. In fact, this is only one of many particular situations in which cement bonds can be found in granular materials. This study adopts similar analytical solutions as those used in the most sophisticated DEM contact models to analyse inter-granular bonds whilst extending their application to different particle sizes, as well as cement content, cement behaviour and realistic particle shapes beyond the commonly used circular/spherical particles. Accounting for different particle shapes can cause the volume of the inter-granular bond to change and hence the magnitude of internal normal and tangential inter-particle forces. On the other hand, at low cement content the bonds may not be contained between rigid particles, but may adhere around a central contact area, similar to water menisci between contacting particles in unsaturated soils. Cement can also adhere to the surface of a particle without the need of pre-existing inter-particle contacts or simply deposited between the void spaces. Incorporating the constitutive behaviour of cement is also important as inter-particle bonds may degrade gradually due to cement breakage resulting in a ductile/brittle response. In this study a more realistic DEM contact model, which accounts for cement content along with particle shape is implemented. Aided by parametric studies we aim to demonstrate that some or all of these features can be accounted for if a full understanding of the micro-mechanics of cemented soils is required. More importantly, it is found that by considering more realistic particle characteristics and appropriate contact models the amount of input parameter calibration required to model cemented soil behaviour can be significantly reduced. Finally, such an approach also ensures reliable micro-mechanical interpretations of the observed macro-scale behaviour of cemented soils.
Author(s): Barreto D, Rouainia M, Nadimi S
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: ASCE Engineering Mechanics Institute International Conference 2021
Year of Conference: 2021
Online publication date: 24/03/2021
Acceptance date: 02/04/2018
Publisher: ASCE
URL: https://emi2020-ic.webspace.durham.ac.uk/
