Details of Grant 

EPSRC Reference:	EP/P010393/1
Title:	PARTICLE-SCALE INVESTIGATION OF SEEPAGE INDUCED GEOTECHNICAL INSTABILITY
Principal Investigator:	O'Sullivan, Professor C
Other Investigators:
Researcher Co-Investigators:
Project Partners:	Arup Group Ltd British Dam Society H R Wallingford Ltd Nantes University Rodney Bridle Tokyo Institute of Technology University of British Columbia (UBC) University of Surrey
Department:	Civil & Environmental Engineering
Organisation:	Imperial College London
Scheme:	Standard Research
Starts:	01 April 2017	Ends:	31 December 2020	Value (£):	387,936
EPSRC Research Topic Classifications:	Ground Engineering
EPSRC Industrial Sector Classifications:	Construction
Related Grants:	EP/P010423/1
Panel History:	Panel Date Panel Name Outcome 04 Oct 2016 Engineering Prioritisation Panel Meeting 4 October 2016 Announced
Summary on Grant Application Form
Civil engineering works often encounter water flowing through the ground. Examples include embankment dams, flood walls and embankments, excavations beneath the water table, tunnels and deep basements. When considering their design, engineers seek to avoid cases where the buoyancy forces exerted by the seeping water are sufficient to reduce the effective stress in the soil to zero, resulting in heave failure or "quicksand". This critical scenario is identified by considering the soil to be a continuous, but porous material. However soil is made up of individual particles of varying size and shape. Awareness is growing that seepage forces imparted on the particles can preferentially erode the smaller particles in sandy soils. There can be significant internal erosion of the soil under scenarios that are considered safe according to the classical continuum calculations used in engineering practice; this phenomenon is called internal instability. We will improve understanding of internal instability and thereby our knowledge of how to design and assess infrastructure safely, by studying the fundamental, particle scale mechanisms involved. Internationally, several research groups are undertaking relatively large experiments of this problem. The particle-scale emphasis in the proposed research will complement, rather than supplement, these studies. The specific research direction originates from our prior research, recently published experimental data from other groups, and consideration of recently published design guidelines (e.g. the International Levee Handbook) and the proposed modifications to the hydraulic failure guidelines in the Eurocode EC7 for geotechnical design. This cross-institutional proposal will combine experimental expertise in testing transparent soil at the University of Sheffield (UoS) with skills in discrete element modelling (DEM) at Imperial College London (IC). We will use these techniques in their most advanced form. At UoS testing facilities equipped with a laser light source will be developed to enable visualization of particle movement inside soil samples while also using tracer particles to observe fluid flow. The development of a triaxial stress path apparatus where the confining and deviatoric stress can be controlled while making these observations will be a particularly novel aspect of this research. IC will continue to champion the use of high performance computing to enable geomechanics DEM simulations and the project will exploit recent work that was carried out in the Department of Mechanical Engineering to enable DEM simulations to be coupled with computational fluid dynamics (CFD) modelling of the fluid flow. Both UoS and IC have been working independently to examine the problem of internal instability and so this proposal marks a timely collaboration to unify their complementary skill sets. For example the DEM model can provide information about particle stresses that cannot be measured in the laboratory, while instability can be directly observed for real materials in the physical tests without any of the idealizations and assumptions which are inherent in any numerical model. The research will clarify: (i) Which materials are initially susceptible to internal instability with volume change and the conditions whereby a material that initially erodes at a constant volume (i.e. settlement or collapse of the particle structure), transitions to having volume change. (ii) Whether seepage velocity or hydraulic pressure gradient correlates better with the initiation of erosion. (iii) How the stress level influences susceptibility; particularly considering stress anisotropy and the relation between principal stress orientation and seepage direction.
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