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Transcript
Climate Change Impacts on the Physical and Mechanical Performance of Stabilised/Solidified Contaminated Soil Sinéad Smith and Abir Al-Tabbaa Cambridge University 29th – 31st May 2007 Outline of presentation Background Laboratory experiments Experimental results Conclusions Background Laboratory experiments Experimental results Conclusions Background SUBR:IM Containment systems S/S remediation suitable for highly contaminated sites Dual physical and chemical process Climate change predictions Context of research within larger consortium UK Climate Impacts Programme (UKCIP 02) +4°C by 2080, rainfall -60% (summer) and +40% (winter) Expected impacts Cyclic wet/dry and freeze/thaw conditions cause deterioration including strength loss and contaminant leachability increase Background Laboratory experiments Experimental results Conclusions Laboratory experiments Summary Laboratory climate scenarios based on UKCIP 02 Temperature Rainfall Parameters under investigation Water content Physical observations Permeability Unconfined compressive strength (UCS) Laboratory climate scenarios Temperature Year Summer Winter 20°C 20°C 2050 27°C -2°C 2080 31°C 0°C Current climate (control conditions) Laboratory climate scenarios Rainfall A/B Scenario Summer Winter Dry summer Dry with no water recharge A: Fully immersed in water (Flooded) B: Maintained at its natural water content (Saturated) C/D Control Intermittent summer rainfall Alternate weeks dry (40% RH) then recharged (100% RH) Constant 100% RH C: Flooded D: Saturated Laboratory soil samples Systems S/S systems Code Uncontaminated SSUS Contaminated SSCS Aged, uncontaminated ASSCS Aged, contaminated ASSUS Laboratory soil samples Composition Samples Soil: Made ground 45% gravel, 15% sand, 20% silt, 20% clay 20% water content Grout: Ø 100 mm, h 100 mm or 50 mm 10: 1 OPC: bentonite 1.6: 1 dry grout: water Contaminants: Pb 2801 mg/kg Cu 1264 mg/kg 3.7: 1 soil: grout Laboratory soil samples Accelerated ageing Equivalent age calculated based on ‘activation energy’ concept Activation energy (Ea ) defines temperature sensitivity of the hydration process of a particular cementitious mix t te e Ea 1 1 R T T0 0 t te Δt T T0 R Equivalent age Curing period (10 months) Curing temperature (60°C) Ambient temperature (20°C) Universal gas constant (8.31 J/ mol.K) Equivalent ages ASSUS ASSCS te = 26 years te = 14 years Background Laboratory experiments Experimental results Conclusions Experimental results Summary Physical observations Water content Permeability Unconfined compressive strength (UCS) Physical observations Control No change SSCS B (2080) Dry summer (A/B) 1st summer: SSCS damaged (2080>2050), SSUS undamaged 1st Summer 1st winter: SSUS A (2050) severely damaged but negligible damage to A (2080) and B (2050, 2080); SSCS damaged further 1st Winter SSUS A (2050) 1st Winter Physical observations Intermittent summer rainfall (C/D) 1st summer: Fine hairline cracks appeared SSUS C (2080) 1st winter: C (2080) severely damaged but negligible damage to D (2080) 1st Summer Aged, intermittent summer rainfall (D) Similar physical damage as unaged system Physical damage to ASSCS identical to ASSUS 1st Winter Water content 20% Dry summer (A/B) Water content reduces to 3% after 4 to 6 weeks Water content (%) SSUS, 2080A SSUS, 2080B SSUS, Control 15% 10% 5% 0% 0 Intermittent summer rainfall (C/D) Water content fluctuates between 7% and 19% 10 Time (months) 15 20 SSUS A/B (2080) 20% Water content (%) 5 SSUS, 2080C SSUS, 2080D 15% 10% 5% 0% 0 5 SSUS C/D (2080) 10 Time (months) 15 20 Water content Contaminated, dry summer (A/B) SSCS similar to SSUS 20% Water content (%) 15% 10% SSCS, 2080B SSCS, 2050B SSCS, Control 5% 0% Aged, intermittent summer rainfall (D) 0 5 10 Time (months) 15 20 SSCS A/B (2050, 2080) 20% Higher water content (9% 14%) than unaged system (7%) Contaminants prevent moisture loss in dry week Water content (%) 15% 10% 5% ASSUS, 2080D ASSCS, 2080D 0% 0 1 2 Time (months) 3 ASSUS & ASSCS D (2080) 4 5 Permeability Dry summer (A/B) Permeability (m/s) 1.E-05 SSUS, 2050A SSUS, 2050B SSUS, Control 1.E-06 1.E-07 2050: Large increase (2 to 1.E-08 3 orders of magnitude) 1.E-09 after 1st summer 1.E-10 No visible damage 1.E-11 Smaller changes thereafter 0 for saturated case Higher value for flooded SSUS case after 1st winter 5 10 Time (months) 15 A/B (2050) 2080: Similar to 2050, fluctuations demonstrate sensitivity to crack patterns Permeability (m/s) 1.E-05 20 SSUS, 2080A SSUS, 2080B SSUS, Control 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 0 5 SSUS A/B (2080) 10 Time (months) 15 20 Permeability Intermittent summer rainfall (C/D) Similar to dry summer (A/B), large increase (2 to 3 orders of magnitude) after 1st summer No apparent effect of visible cracks Small changes thereafter for saturated case Highest value for flooded case after 1st winter 1.E-05 Permeability (m/s) SSUS, 2080C SSUS, 2080D SSUS, Control 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 0 5 SSUS C/D (2080) 10 Time (months) 15 20 Permeability Similar trend for SSCS as SSUS but 1 order of magnitude higher Large increase after 1st summer (2 orders of magnitude) then constant Aged, intermittent summer rainfall (D) Both ASSUS and ASSCS gradually increase 1 order of magnitude Opposite trend – contaminants reduce permeability by 1 order of magnitude 1.E-05 Permeability (m/s) Contaminated, dry summer (A/B) 1.E-06 1.E-07 SSCS, Control SSCS, 2080B SSCS, 2050B 1.E-08 1.E-09 1.E-10 1.E-11 0 5 10 Time (months) 15 20 SSCS A/B (2050, 2080) 1.E-05 ASSUS, 2080D ASSCS, 2080D 1.E-06 Permeability (m/s) 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 0 5 10 Time (months) ASSUS & ASSCS D (2080) 15 20 Unconfined Compressive Strength Control Generally constant but high variability (crack patterns?) 10 SSUS, Control 8 UCS (MPa) 6 4 2 Dry summer (B) and intermittent summer rainfall (D) Generally lower than control 0 5 10 15 20 Time (months) SSUS Control 10 SSUS, 2080B SSUS, 2050B SSUS, 2080D 8 UCS (MPa) 0 6 4 2 0 0 5 10 Time (months) 15 SSUS B (2050, 2080) & D (2080) 20 Unconfined Compressive Strength Contaminated, dry summer (A/B) and control 10 SSCS, Control SSCS, 2080B SSCS, 2050B 8 UCS (MPa) Control similar to SSUS but half the value 6 4 2 0 0 5 10 Time (months) 15 20 SSCS B (2050, 2080) Aged, intermittent summer rainfall (D) Higher than SSUS control Similar values for both ASSUS and ASSCS 10 ASSUS, 2080D 8 UCS (MPa) ASSCS, 2080D 6 4 2 0 0 5 10 Time (months) ASSUS & ASSCS D (2080) 15 20 Background Laboratory experiments Experimental results Conclusions Conclusions Without climate effects, properties were constant with time. Contamination caused permeability to increase by 1 order of magnitude and UCS to decrease by half. Climate change scenario causing most damage was intermittent summer rainfall and flooded winter. For unaged systems, permeability generally increased by 2 to 3 orders of magnitude after 1st summer then remained constant. Low correlation between visible damage and permeability. UCS decreased with time. Accelerated ageing results indicate that long-term properties of S/S remediated soils may improve their resistance to climate change impacts. Thank you for listening Questions