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Cementation of Sands

Cementation of Sands. Brina Mortensen ECI 281A - Advanced Soil Mechanics UC Davis December 4, 2006. Outline. Purpose of Research Types of Cementation Microbial Induced Calcite Precipitation (MICP) Properties of Cementation Process Monitoring Future Research. Purpose of Research.

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Cementation of Sands

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  1. Cementation of Sands Brina Mortensen ECI 281A - Advanced Soil Mechanics UC Davis December 4, 2006

  2. Outline • Purpose of Research • Types of Cementation • Microbial Induced Calcite Precipitation (MICP) • Properties of Cementation • Process Monitoring • Future Research

  3. Purpose of Research • Development of biological soil improvement technique to resist liquefaction in sand deposits • Determine the feasibility and practicality of implementing method in practice. • Building upon previous research that has established successful treatment of soil samples at the laboratory and model scales.

  4. Natural Cementation Deposits • Created through chemical deposition and chemical processes associated with weathering. • Precipitation of calcite, silica, alumina, iron oxides, and salts. • Calcite precipitates by: • Deposition from water saturated with calcium carbonate • Chemical exchanges at the water-soil grain surface interface.

  5. Artificial Cementation • Improve properties of sand deposits by filling void spaces and adding strength • Cementing agents include lime, cement, asphalt • Cementation added to in-situ soil state by non-displacement methods

  6. Microbial Induced Calcite Precipitation (MICP) • Calcite Cement occurs as a consequence of bacterial metabolic activity • Bacillus pasteurii uses urea as an energy source, produces ammonia and carbon dioxide • Rise in pH due to production of ammonia and carbon dioxide from hydrolysis of urea • Increase in pH causes Ca2+ and CO32- to precipitate as CaCO3 • Rise in pH causes microbes to act as nucleation site for crystallization

  7. MICP in Laboratory • Microbial cementation achieved from a solution of Bacillus pasteurii, urea, and CaCl2 • Solution flushed through soil, set up for minimum of 4 hours to allow microbes to bind to soil skeleton • Subsequent flushes of urea-CaCl2 solution • Air injected to supply bacteria with required oxygen for respiration • Flushes continued until desired level of improvement is reached

  8. Properties of Cementation • Cementation adds stiffness to sand • Stiffness can be monitored with shear wave velocity • Increase in Gmax with increase in cement content • Determine Gmax from shear wave velocity: Gmax = t * Vs2 DeJong et al., 2006

  9. Previous Results Global Axial Strain (%) Increase in undrained shear strength Degradation of cementation during shear DeJong et al., 2006

  10. Process Monitoring • Bender Elements used to determine shear wave velocity • Piezoelectric plates oscillate when electrically excited by changing voltage • Oscillation creates shear wave within specimen • Induced shear wave causes oscillation and voltage response in receiving bender element Santamarina, 2001

  11. Bender Element Santamarina, 2001

  12. Future Research • Dynamic properties of improved soil • Cyclic Simple Shear Tests • Centrifuge Modeling • Model of field scale grouting method

  13. References • Santamarina, J. Carlos, (2001) Soils and Waves: Particulate Materials Behavior, Characterization and Process Monitoring, John Wiley & Sons. • Mitchell, James K., (1993) Fundamentals of Soil Behavior, 2nd Edition, John Wiley & Sons. • DeJong, Jason T., Fritzges, Michael B., and Nusslein, Klaus, (2006), “Microbially Induced Cementation to Control Sand Response to Undrained Shear,” Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers, November. • Fitzges, M. F. (2005), “Biologically induced improvements of the response of sands to monotonic loading.” MS thesis, University of Massachusetts, Amherst, Mass.

  14. Questions?

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