Explain fundamental concepts relating to soil fabric, formation, and mineralogy, Lecture notes of Geotechnical Engineering

Download Explain fundamental concepts relating to soil fabric, formation, and mineralogy and more Lecture notes Geotechnical Engineering in PDF only on Docsity! 1 I. Soil Formations 2 Outline of the First Topic 1. Soil Formations and Deposits 2. Phase Relations 3. Some Thoughts about the Specific Gravity Measurements 5 1.2 Bowen’s Reaction Series  The reaction series are similar to the weathering stability series. •More stable •Higher weathering resistance (Das, 1998) 6 Question What is the main mineral of the sand particles in general? Quart z 7 1.3 Weathering 1.3.1 Physical processes of weathering  Unloading – e.g. uplift, erosion, or change in fluid pressure.  Thermal expansion and contraction  Alternate wetting and drying  Crystal growth, including frost action  Organic activity – e.g. the growth of plant roots. 1.3.2 Chemical Process of weathering  Hydrolysis – is the reaction with water –will not continue in the static water. –involves solubility of silica and alumina  Chelation –Involves the complexing and removal of metal ions .  Cation exchange – is important to the formation of clay minerals  Oxidation and reduction.  Carbonation –is the combination of carbonate ions such as the reaction with CO2 1.3.3 Factors affect weathering  Many factors can affect the weathering process such as climate, topography, features of parent rocks, biological reactions, and others.  Climate determines the amount of water and the temperature. (Mitchell, 1993) 5 2. Phase Relations To be discussed in lec5 10 11 2.1 Three Phases in Soils S : Solid Soil particle W: Liquid Water (electrolytes) A: Air Air 12 2.2 Three Volumetric Ratios (1) Void ratio e (given in decimal, 0.65) (2) Porosity n (given in percent 100%, 65%) (3) Degree of Saturation S (given in percent 100%, 65%) )V(solidsofVolume )V(voidsofVolume e s v )V(samplesoilofvolumeTotal )V(voidsofVolume n t v %100 )V(voidsofvolumeTotal )V(watercontainsvoidsofvolumeTotal S v w  e1 e )e1(V eV n s s     15 2.2.1 Engineering Applications (e)(Cont.) SC e = 0.91 CT e = 0.65 The finer particle cannot pass through the void •Clogging Critical state soil mechanics Filter 16 2.2.2 Engineering Applications (S) Completely dry soil S = 0 % Completely saturated soil S = 100% Unsaturated soil (partially saturated soil) 0% < S < 100% Demonstration: Effects of capillary forces Engineering implications: Slope stability Underground excavation %100 )V(voidsofvolumeTotal )V(watercontainsvoidsofvolumeTotal S v w  17 2.2.2 Engineering Applications (S) (Cont.) • 80 % of landslides are due to erosion and “loss in suction” in Hong Kong. • The slope stability is significantly affected by the surface water. (Au, 2001) 20 2.4 Weight Relationships (Cont.) Submerged unit weight: Consider the buoyant force acting on the soil solids: Archimede’s principle: The buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that object. wsat'  wsat t wtws t wwts t wwts t wss V VWW V WVW %)100S( V )VV(W V VW          21 2.4.1 Engineering Applications (w) • For fine-grained soils, water plays a critical role to their engineering properties (discussed in the next topic). • For example, The quick clay usually has a water content w greater than 100 % and a card house structure. It will behave like a viscous fluid after it is fully disturbed. Clay particle Water (Mitchell, 1993) 22 2.5 Other Relationships (1) Specific gravity (2) Proof: w s w s sG       s sw GweS weS   s w w w s s s w w s s w s s w s v v w s V V V M V M M M M M Gw V V V V V V eS GweS       25 3. Some Thoughts about the Specific Gravity (Gs) Measurement 26 3.1 Standards Standards  ASTM D854-92 Standard Test Method for Specific Gravity of Soils  ASTM C127-88 (Reapproved 1993) Test Methods for Specific Gravity and Absorption of Coarse Aggregate.  BS 1377: Part 2:1990 27 3.2 Alternatives • If the soil contains soluble salts or can react with water, an alternative liquid should be used such as kerosene (paraffin) or white spirit. Note that the density of oil is not equal to 1 g/cm3, L1 g/cm3 (Head, 1992). )mm()mm( )mm( )mm()mm( )mm( G 2314 12 2314 12 s L L        Weight of liquid displaced by the soil solid. 30 3.4 Average Specific Gravity Values 2s 2 1s 1 avgs 2 2 21 2 1 1 21 1 avgs 21 2121 21 avgs G 1 P G 1 P 1 G W V )WW( W W V )WW( W 1 G )WW( )VV( 1 )VV( )WW( G                For example, For soil particles larger than 2mm, the weight is W1 and the volume is V1. For soil particles smaller than 2mm, the weight is W2 and the volume is V2. P is the weight fraction 2 GG 2s1s  31 4. References Main References: Das, B.M. (1998). Principles of Geotechnical Engineering, 4th edition, PWS Publishing Company. (Chapter 2) Holtz, R.D. and Kovacs, W.D. (1981). An Introduction to Geotechnical Engineering, Prentice Hall. (Chapter 2) Others: Geological Landscapes of Hong Kong, Hong Kong Geological Survey. Giancoli, D.C. (1998). Physics, 5th edition, Prentice Hall. Goodman, R.E. (1989). Introduction to Rock Mechanics, 2nd edition, John Wiley & Sons. Guide to Rock and Soil Description (1988). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong. Head, K. H. (1992). Manual of Soil Laboratory Testing, Volume 1: Soil Classification and Compaction Test, 2nd edition, John Wiley and Sons. Ifran, T. Y. (1996). Mineralogy, Fabric Properties and Classification of Weathered Granites in Hong Kong, Quarterly Journal of Engineering Geology, vol. 29, pp. 5-35. Irfan, T.Y. (1999). Characterization of Weathered Volcanic Rocks in Hong Kong, Quarterly Journal of Engineering Geology, vol. 32, pp. 317-348. Lambe, T.W. and Whitman, R.V. (1979). Soil Mechanics, SI Version, John Wiley & Sons. Mitchell, J.K. (1993). Fundamentals of Soil Behavior, 2nd edition, John Wiley & Sons.