Micromechanics of seismic wave propagation in granular materials
Lead Research Organisation:
University of Bristol
Department Name: Civil Engineering
Abstract
This research uses sophisticated laboratory testing and advanced numerical modelling to consider the dual problem of wave propagation in granular soils and estimation of stiffness. Understanding how stress waves propagate through soils is essential for earthquake engineering analysis and correct interpretation of current in-situ and laboratory seismic investigation results while accurate description of the soil stiffness is central for predictions of ground movements during and after construction. Soils are described as continua at scales which are large in comparison with the particle size, but this continuum response is a consequence of the particulate nature of the material. Discrete element modelling (DEM) describes the macroscopic response of particulate systems from integration of the mechanical interactions between particles. Computing power now permits the 3D analysis of assemblies of spherical particles with the actual dimensions of advanced laboratory tests. Sophisticated laboratory testing will be performed in a flexible boundary Cubical Cell permitting independent control of three principal stresses with fixed principal axes. Materials to be tested will include an angular sand, a rounded sand, and glass ballotini of two sizes: a size which matches the test sands and the larger size used in the DEM simulations. The influence of the nature of the granular material will be examined by increasing the complexity of the material in phases: starting with smooth spherical ballotini, then roughened ballotini, then real, irregular soil particles.Parallel DEM and multiaxial testing will be used to develop understanding of (1) the propagation through cubical samples of different granular materials of 'seismic' waves generated by piezoceramic elements; (2) the evolution of stiffness anisotropy with general histories of principal stresses; and (3) the effect of particle size and shape on the stiffness properties of granular materials.There will be three important outcomes: (1) testing and simulating the same system will provide important information on the reliability of DEM models to simulate wave propagation and on the level of detail in the DEM model required for accurate simulation; (2) testing of a range of different granular materials will show how results of DEM simulations of ideal particles can inform prediction of real soil response of real soils (under stress conditions which cannot be attained in the laboratory for example); and (3) knowledge of the nature of wave propagation and the evolution of small strain stiffness of geomaterials will inform the interpretation of laboratory and field tests.
Publications
Cavarretta I
(2012)
Characterization of artificial spherical particles for DEM validation studies
in Particuology
Ibraim E
(2018)
Energy efficiency of fibre reinforced soil formation at small element scale: Laboratory and numerical investigation
in Geotextiles and Geomembranes
Camenen J
(2013)
Experimental and numerical assessment of a cubical sample produced by pluviation
in Géotechnique Letters
O'Donovan J
(2016)
Micromechanics of seismic wave propagation in granular materials
in Granular Matter
J. O'Donovan
(2014)
Micromechanics of seismic wave propagation in granular materials
Otsubo M
(2015)
Quantitative assessment of the influence of surface roughness on soil stiffness
in Géotechnique
Description | Complex responses to perturbations in granular materials generated by point vibrational sources in experiments were compared to those found by the controlled movement of the particles in numerical simulations. The generally satisfactory agreement between experimental observations and simulations can be seen as a validation and support the use of numerical to investigate the influence of grain interaction on wave propagation in soils. These results allowed understanding of how waves propagate and suggest way for interpretation which can be directly applied to the stiffness characterisation of soils. The stiffness is one of the most important parameters that governs the behaviour of structures in the serviceability limit. Underestimation of the stiffness parameters results in excessive settlements while their overestimation results in increased project costs. The use of linear elements inserted into material appears problematic as some perturbation of the material structure may have consequences on the interpretation. The local contact between these elements and the particles also affects the results. It is also important to emphasise that the small vibrations induce the system to respond according to its dynamic characteristics and that opens the idea of using solutions for the system's resonance for stiffness calculation avoiding the use of the results in the time domain. |
Exploitation Route | The technique of soils stiffness evaluation based on wave propagation is extensively used by industry. However, the interpretation of the arrival time is still a topic under discussion. This project helps clarifying this important issue and provide a base for interpretation and calculation of the stiffness parameters. |
Sectors | Construction |
Description | This research explored fundamental aspects related to granular soils behaviour. Understanding how the waves propagate through soils is relevant and impacts not only the safety and costs of geotechnical and stuctural projects but also other areas like geophysics and earthquake engineering. |
Sector | Construction |
Impact Types | Economic |
Description | Newton Research Collaboration Programme |
Amount | £8,000 (GBP) |
Funding ID | NRCP1415/2/2 |
Organisation | Royal Academy of Engineering |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 03/2015 |
End | 03/2016 |
Description | Experimental and numerical investigation of the wave propagation arrival time through granular soils |
Organisation | University of Lisbon |
Country | Portugal |
Sector | Academic/University |
PI Contribution | This collaboration is based on the results generated by the research proposal. The data brought the attention of our colleagues in Portugal and following some preliminary discussions and meetings, we have decided to embark into a more structured research collaboration which will include development of numerical tools and laboratory data interpretation. |
Collaborator Contribution | our partners in Lisbon and Minho have developed numerical models that treat the wave propagation through multi-phase media. These numerical models have not been extensively tested and validated and our experimental data in Bristol can provide the ideal benchmark for such work. The importance of understanding the way in which waves propagate through soils as well as their interpretation in view of detecting key soil characteristics are extremely important for civil engineering and geophysics projects. |
Impact | We are planning to produce at least 4 papers in the next year. |
Start Year | 2019 |
Description | Experimental and numerical investigation of the wave propagation arrival time through granular soils |
Organisation | University of Minho |
Country | Portugal |
Sector | Academic/University |
PI Contribution | This collaboration is based on the results generated by the research proposal. The data brought the attention of our colleagues in Portugal and following some preliminary discussions and meetings, we have decided to embark into a more structured research collaboration which will include development of numerical tools and laboratory data interpretation. |
Collaborator Contribution | our partners in Lisbon and Minho have developed numerical models that treat the wave propagation through multi-phase media. These numerical models have not been extensively tested and validated and our experimental data in Bristol can provide the ideal benchmark for such work. The importance of understanding the way in which waves propagate through soils as well as their interpretation in view of detecting key soil characteristics are extremely important for civil engineering and geophysics projects. |
Impact | We are planning to produce at least 4 papers in the next year. |
Start Year | 2019 |
Description | Micromechanics of seismic wave propagation in granular materials |
Organisation | Imperial College London |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Experimental investigation of wave propagation through granular media and stiffness evaluation. |
Collaborator Contribution | Numerical investigation of wave propagation through granular media and stiffness evaluation. |
Impact | Three journal and two conference papers have jointly been published but several publications are in advanced stage of preparation. |
Start Year | 2009 |
Description | UK-Brazil research collaboration: advanced laboratory testing and modelling of treated soils |
Organisation | Federal University of Rio Grande do Sul |
Country | Brazil |
Sector | Academic/University |
PI Contribution | We worked together with our partner on characterisation of cemented materials. |
Collaborator Contribution | The partner sent to Bristol a PhD student for one year. |
Impact | One journal paper has been submitted already and several journal papers (four) are in progress of submission. |
Start Year | 2015 |
Description | Annual National Workshop: Micro-macro geomaterials |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | This type of workshops are very engaging, stimulating and provide an excellent environment for discussions and ideas exchanges. The feedback received following the presentations was used to adjust procedures, improve data analysis. |
Year(s) Of Engagement Activity | 2010,2011,2012,2013,2015 |
Description | Organising International Workshop "Wave Propagation and Soil Stiffness: Particle-Continuum Duality" |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Type Of Presentation | workshop facilitator |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | To mark the completion of this research project, a workshop entitled "Wave Propagation and Soil Stiffness" was held in Bristol on March 20 and 21. The dates were chosen to coincide with the BGA Rankine lecture. A total of 71 participants attended the workshop, about 40 of whom are based in the UK, with the remaining participants coming from diverse locations including Argentina, Japan, Portugal, Germany, Italy, the Netherlands, USA, Mexico, and Australia. 20 minute presentations were delivered by 16 invited speakers (three of the speakers were young geotechnical engineers who have been involved in the project), with the discussion on March 20 focussing on experimental studies, while the session on March 21 considered theoretical and numerical studies. The workshop was jointly supported by TC101 and TC105 of the International Society of Soil Mechanics and Foundation Engineering, the British Geotechnical Association and the Institution of Civil Engineers. The workshop contributed to knowledge transfer and interaction between academia and industry, facilitating the rapid application and exploitation of recent research findings. During the workshop emphasis was placed on best practice in setting up the tests, interpreting the results to obtain appropriate parameters and developing a firm theoretical understanding of the mechanics underlying the tests. Ample time was provided for discussions and exchanges of good practice. |
Year(s) Of Engagement Activity | 2014 |
URL | http://www.bristol.ac.uk/engineering/events/2013/98.html |
Description | Wave Engineering Bristol Workshop: Wave propagation through granular soils: active probing and passive monitoring |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Postgraduate students |
Results and Impact | The workshop was attended by researchers from different communities: physics, mathematics, as well as from industry. |
Year(s) Of Engagement Activity | 2017 |
URL | https://waveengbristol.wordpress.com/workshops/web-2017/ |