Biochemical methods for soil improvement

Transcription

1 Biochemical methods for soil improvement YELGIP Workshop October 2006 dr. Vicky Whiffin

2 Overview Introduction Biological effects on soil properties Physical effects Chemical effects Challenges and Conclusions 2

3 Understanding soil behaviour Mechanics Geology Mineralogy Soil behavior Biology? 3

4 Biogeochemistry in the soil but can biology really influence soil properties? 4

5 Are there any bacteria in there? bacteria in 1 kg of soil All kinds with lots of roles Decomposition of organic matter Nutrient cycling what if we could get them to work for us? Involved in almost every chemical transformation in the soil Can be active or inactive depending on availability of suitable nutrients 5

6 What do bacteria look like?? 6

7 Bacteria as micro-geotechnical engineers Convincing bacteria to work for us by: Bio-stimulation addition of suitable nutrients to activate desired organisms Bio-augmentation addition of specialist bacteria to do the job From Macro to Micro 7

8 Biological effects on soil particles Thursday, 02 November 2006 Local interations of bacteria on mineral surfaces Grain weathering or precipitation surfaces Soil particle Micro-alterations can have macro-effects on soil properties (e.g. fines migration) 8

9 Influenceable soil properties PHYSICAL Permeability Strength Grain size CHEMICAL Pollution 9

10 PHYSICAL Soil Improvements - Seepage & Bioclogging - Strength & Stiffness 10

11 Seepage & Bioclogging Biological clogging to reduce seepage in undesired locations (e.g. construction pits) Redirection of flow paths Soil particle Clogging can be short or long-term 11

12 Example: Bio-sealing Complex mechanism Includes: Biofilm/EPS (exopolysaccaride) slime formation Mineral erosion (weathering) from soil particles and entrapment Reactants automatically locate leaking zones by mixing with water flow 12

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14 Practical application HSL Haarlemmermeer Thursday, 02 November 2006 Clay Sand Break in water barrier Water flow 14

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16 Effect on water flow Leaking areas Tunnel position Before 9 weeks injection later 16

17 Strength & Stiffness Precipitation of minerals inside the soil structure Minerals can provide bridging strength between particles Significant strength improvement possible 17

18 Example: Biological CaCO 3 precipitaton Precipitaton of CaCO 3 in the soil pores for soil strengthening In sand similar result as sandstone Soil retains permeability Strengths up to 30 Mpa Biological CaCO 3 formed by specialist Coccolithophores 18

19 100 micrometer (10-4 m) Van Paassen Animations

20 1 millimeter (10-3m) Van Paassen Animations

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23 CaCO 3 CaCO 3 CaCO 3

24 Unconfined compressive strength Thursday, 02 November Stress (MPa) m Strain 24

25 CHEMICAL Soil Improvements - Bioremediation 25

26 Bioremediation Biological cleaning process for contaminated soils In-situ Most applicable to sand (due to accessability) Addition of limiting nutrient(s) to promote existing bacteria to degrade pollutant 26

27 Bioremediation 27

28 Air sparging Thursday, 02 November

29 Conclusions Bacteria are present in all soils! Biology can play a significant role in soil improvement Effects can be physical or chemical Micro effects can have Macro results! 29

30 Further information (English) Or (Dutch) 30