ACHILLES Lon Long-term De Deterioration of f Lin Linea ear Infr Infrastructure Monday 04 February 2019 Friends’ House London, UK
Agenda 1500 Welcome, background and introduction Prof Stephanie Glendinning (Newcastle) 1520 Modelling of weather-driven deterioration Prof Neil Dixon (Loughborough) 1550 Improving inputs to models Prof David Toll (Durham) 1610 Asset behaviour and performance Prof William Powrie (Southampton) 1625 Forecasting and decision support at network scale Prof Darren Wilkinson (Newcastle) 1640 Discussion and next steps Prof Stephanie Glendinning (Newcastle) 1700 end of meeting ACHILLES – an EPSRC Programme Grant
introduction Who we are and how we get here EPSRC funding support - Stakeholders/project partners increasingly embedded • 2004-2009 BIONICS • Research facility led by Newcastle with Loughborough, Leeds, Bristol, Durham, Dundee, Nottingham Trent, BGS… • A large group of partners including HA (now HE), NR, MottM , Skanska, CIRIA… • Constructed a full scale embankment testing facility that continues to deliver data/insights • 2005- 3-year start-up funding for CLIFFS • A national network led by Loughborough • Connected a large group of people interested in climate impact forecasting for slopes spanning multiple disciplines • 2009-2013 FUTURENET • Led by Birmingham with Loughborough, Nottingham, TRL, BGS, HR Wallingford • Evaluated the look of the UK transport network in the 2050s • 2013-2017 iSMART • Led by Newcastle, with Loughborough, Queen’s Belfast, Southampton, BGS, Durham • Delivered insights into deterioration of transport infrastructure geotechnical assets • PLUS MANY OTHER RELATED PROJECTS • 2018- ACHILLES – a programme grant building on this previous work ACHILLES – an EPSRC Programme Grant
introduction Context xt • The UK’s transport infrastructure is one of the most heavily used in the world • The UK rail network takes 50% more daily traffic than the French network • The M25 between junctions 15 and 14 carries 165,000 vehicles per day • London Underground: Europe's largest metro subway system but also the oldest • Much of the rail network is over 100 years old • Not just transport assets One incident near 00:30 Birmingham New Street resulted in a total of 4900 delay minutes along the network for the next 12 hours ? After Jaroszweski et al. (2015), Meteorological Applications ACHILLES – an EPSRC Programme Grant
introduction Evid idence at t th the asset scale le – numerical modelli ling Model couples hydrological model SHETRAN with FLAC Models the influence of meteorological parameters and climate (change) on slope behaviour Long-term deterioration modellin ing • Following equilibrium, deterioration continues at slower rate • Influence of extremes will become more significant as FoS approaches 1 ACHILLES – an EPSRC Programme Grant
Introduction Evid idence of materia ial scale le deterioration Evidence from both the laboratory and field • Soil water retention • laboratory investigations • from field monitoring • Permeability/hydraulic conductivity • field investigations • permeability functions • Strength • water content • suction • Cracking • at the micro-scale and effect of freeze-thaw • at the macro-scale (cracking) ACHILLES – an EPSRC Programme Grant
introduction Current approaches to asset management Network Rail – Earthworks technical strategy ACHILLES – an EPSRC Programme Grant
introduction Asset deterioration – ACHILLES programme Generalised deterioration model for transport earthworks (adapted from Thurlby, 2013). ACHILLES – an EPSRC Programme Grant
Modelling deterioration Modelli ling approach: Key fin indin ings from iS iSMART • There is conclusive evidence for seasonal ratcheting progressive failure mechanisms in constructed slopes • However, it remains challenging to model this seasonal ratcheting mechanism • Use of an unsaturated framework is critical • Key input parameters are: • high permeability near surface layer (measured in the field) • Soil water retention curves (SWRC) • stiffness distribution • strength behaviour • cracking • Non-local strain minimises mesh dependency • Weather represented using two approaches: Pore pressure cycling and coupling with ‘weather generator’ to account for current and future climates • Able to produce ‘deterioration’ curves and investigate effects of design • Our models can replicate measured pore water pressures in a slope and weather driven progressive failure – the approach has been validated ACHILLES – an EPSRC Programme Grant
Modelling deterioration The near-surface condition and pore water r pressures • It critically controls the rate at which an earthwork responds to weather • Near-surface permeability measurements for earthworks sparse in the literature • Detailed information from Newbury to compare simulations, including parametric study to define near-surface layers Model calib libration and valid lidation • Developed a methodology to allow the influence of meterological parameters and climate on a slope to be investigated • Model makes use of coupling between SHETRAN and FLAC with Two Phase Flow • Modelling approach calibrated using Newbury Cutting and Take and Bolton Centrifuge tests ACHILLES – an EPSRC Programme Grant
Modelling deterioration Model valid lidation of seasonal ratcheting • Kaolin slope (modelled/experimental [Take and Bolton 2011]) • Magnitude and nature of mid-slope and toe displacements are very good • This is great news as progressive failure begins at toe • And it is supported by independent observations Numeric ical l models ls of seasonal ratcheting • Demonstrates simplistic, transient factor of safety method for two scenarios; • Again, shows significance of wet years on the performance of a slope compared to gradual deterioration under continued seasonal cycles. ACHILLES – an EPSRC Programme Grant
Modelling deterioration Fast-Track Modellin ing – Cut Slo lopes • Newbury Cutting • Climate Study • Intervention / Maintenance Study • Geometric Study • Embankment Study Newbury Cutting (A34) Smethurst and Clarke (N.D.) ACHILLES – an EPSRC Programme Grant
Fast-track modelling ACHILLES fast-track modelli ling • High permeability near surface • Evidence from the field shows that cut slope near surface high permeability zone develop rapidly • Vegetation rooting mechanical contribution to soil strength • Prior models account for vegetation root influence on suction generation and effective stress but NOT root influence on strength • Used to investigate effects of different remediation strategies • Slope regrading • Toe drainage • Shear key at toe • Soil nails ACHILLES – an EPSRC Programme Grant
Modelling deterioration Fast track modelli ling work: Future • Embankment model assumptions • Road • Impermeable pavement at crest • Assume drains at road edges effectively remove runoff • High relative strength and stiffness of fill (replicate high quality compaction) • Minimised spatial heterogeneity • Rail • Permeable crest - Ballasted • None existent drainage • Lower relative strength and stiffness of fill (replicate end tipped construction) • Increased heterogeneity ACHILLES – an EPSRC Programme Grant
Improving inputs to models Deterioration in inputs to models Evidence from the laboratory and field • Soil water retention • laboratory investigations • from field monitoring • Permeability/hydraulic conductivity • field investigations • permeability functions • Strength • water content • suction • Cracking • at the micro-scale and effect of freeze-thaw • at the macro-scale (cracking) ACHILLES – an EPSRC Programme Grant
Improving inputs to models Soil il water retention Field and lab experiments • wetting and drying cycles • progressive loss of suction for same water content Hydraulic ic conductiv ivit ity Large test programme to characterise hydraulic conductivity • in the top 1.5 m several orders of magnitude observed Unsaturated soil il strength • cycling of wetting and drying leads to progressive loss of strength Soil il cracking and deterioration Observations: micro (lab: env SEM) vs macro (field scale crack measurement) • cracks persist and soil deteriorates ACHILLES – an EPSRC Programme Grant
Improving inputs to models Key messages • Rate of change (SWRC and strength) is non-linear - greatest change observed after primary drying. Subsequent rate of change and magnitude is lower BUT cycling effect is continued through extreme events • Macro-scale cracking increasing exposure and influence – it renews and perpetuates W/D cycle effect – deterioration at nano to macro scale. • W/D is a pre-cursor to the initiation of progressive failure - causing the soil at the near surface of an engineered clay slope to reduce in strength without any change in external load. Implications for slope condition (stability) assessment • the need for non-stationarity of soil parameters and ground model , with changes occurring both seasonally and gradually over time. • there is a need for new constitutive soil model (s) that can account for soil deterioration due to wetting and drying ACHILLES – an EPSRC Programme Grant
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