الفهرس 
General introductionOnly 14 pages are availabe for public view
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Abstract
Microbial Geotechnology Is The Use Of Microorganisms And/Or Their Derivatives To Alter Engineering Properties Of Soil For Improving Its Stability, Strength And Stiffness. Ureases Hydrolyze Urea In The Soil Leading To Caco3 Precipitation, Which Binds Soil Particles Together (Biocementation). In This Thesis, Nine Egyptian Soils Were Sampled And Screened For Ureolytic Bacteria. 15 Isolates Were Obtained, And Identified Through Morphological Examination, Vitec Technique And 16S Rrna Gene Sequencing. from The 15 Isolates, 6 Isolates Had The Highest Extracellular Urease Activity. Citrobacter Freundii And Pseudomonas Azotoformans Showed The Highest Extracellular Urease Activities Of 45.5 ± 3.4 And 54.9 ± 3.5 U Ml−1, Respectively And Were Significantly Higher (P < 0.05) Than The Reference Strain (Sp. Pasteurii) By 3–4 Times. Growth Kinetics Were Measured At Different Ph Values And In The Presence Of Molasses As The Sole Carbon Source. When Cell-Free Supernatants Of These Isolates React With Cementation Solution (Urea And Cacl2), A White Preciptate Of Caco3 from Was Formed. The X-Ray Diffraction (XRD) Of The Precipitates Proved The Formation Of Calcite And Aragonite Crystal Forms. Sandy Soil Treated With The Supernatants And Evaluated By Modified Proctor And California Bearing Ratio (CBR) Tests To Determine Any Improvement In Soil Strength. The Obtained Results Showed A Significant Improvement (P < 0.05) In The CBR Values In Soil Treated With Different Supernatant Compared To Untreated Soil (30 ± 0.3%). Sandy Soil Treated With Sp. Pasteurii (DSM33) Showed The Highest Improvement In Un-Soaked CBR Value (49 ± 0.9%), Followed By Ps. Azotoformans (C) With CBR Value (42 ± 0.4%) And C. Freundii (Y2b) With CBR Value Of (40 ± 1.0%). Scanning Electron Microscopy Showed The Caco3 Precipitation Resulting In Reduction Of The Gaps Between Soil Particles, Hence Confirming The Biocementation Phenomenon Which Is Responsible For Soil. The Use Of Urease-Containing Cell-Free Supernatant Rather Than The Whole Microorganism In Biocementation Lowers The Risks Of Spreading Pathogens To The Environment And Altering The Microbial Diversity At The Application Area.