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CE 496 Senior Design

CE 496 Senior Design. Geotechnical Engineering: Soil Properties & Testing Lecture 6 Date: 1/26/2012 Professor Knur. Looking Ahead. Next Three Lectures: Define Project Objectives and Needs Inventory of Geotechnical Data Sampling/Field Procedures Lab Testing Procedures Analyses.

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CE 496 Senior Design

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  1. CE 496 Senior Design Geotechnical Engineering: Soil Properties & Testing Lecture 6 Date: 1/26/2012 Professor Knur

  2. Looking Ahead • Next Three Lectures: • Define Project Objectives and Needs • Inventory of Geotechnical Data • Sampling/Field Procedures • Lab Testing Procedures • Analyses

  3. Sampling/Field Procedures • Double Ring Infiltrometer • Purpose- To obtain Coeff. of Permeability (k)

  4. Sidebar Discussion- k • Coefficient of permeability • a.k.a. hydraulic conductivity • Not a Coefficient at all – It has units of rate = Length/time (L/T) • Reported as cm/sec or ft/day • Units of cm/sec is most common in soil mechanics • Defined as velocity of water through soil

  5. Coefficient of Permeability - k • From Darcy Equation for laminar flow • Q=k*i*A*t • Q= Volume of water (L3) • k= cofficientof permeability (L/T) one dimensional flow • I = hydraulic gradient (Lv/Lh) unitless • A = Cross section area (L2) normal to the direction of flow • t = time (T)

  6. Coefficient of Permeability - k • From Darcy Equation • Q=k*i*A*t Rearrange terms: • k=Q/(i*A*t) Check Units • k= L3/((Lv/Lh)*L2*T) Cancel terms • k = L/T

  7. Range of k • No property in nature has a wider range of Value • Over 10 orders of magnitude

  8. Factors that influence k • Viscosity of water inversely proportional to Temperature

  9. Viscosity of Water

  10. Factors that influence k • Viscosity of water α 1/Temp. • Size of pore spaces • Size and shape of soil grains • Density of soil (packing) • Structure/orientation of soil particles

  11. Size and Shape of Grains

  12. Size and Shape of Grains

  13. Factors that influence k • Viscosity of water α1/Temp. • Size of pore spaces • Size and shape of soil grains • Density of soil (packing) • Structure/orientation of soil particles • Interconnectedness of pores • Presence of discontinuities • Cementation

  14. Basic Assumptions Inherent in k • Soil is homogenous • Voids are completely filled with water • No consolidation or expansion occurs • Soil and water are incompressible • Flow is laminar (one dimension) • Darcy’s Law is valid

  15. Back to Double Ring Infiltrometer

  16. Double Ring Infiltrometer • Since water will tend to flow outwards in three dimensions, measurement using single ring is not accurate

  17. Double Ring Infiltrometer • Outer ring water fills soil voids in lateral dimension • Leaving inner ring to vertical flow • The inner ring must be significantly smaller than the outer ring

  18. Double Ring Infiltrometer • Measure volume of water it takes to maintain level in each ring separately • Looking for steady-state condition

  19. Double Ring Infiltrometer • Value is still not a “true” coefficient of permeability since the we are not guaranteed that flow is one dimensional • Use of a pumping and drawdown well is best • Average rate over very large area

  20. Other Methods to Determine k From Cedergren, 1989, pg.33

  21. Other Methods to Determine k • Correlate to Curves- But use with caution (DACE, EM1110-2-1901, 1986, pg2-29) (NAVFAC Dm7.1,1986, pg. 139)

  22. Results From Our Field Study • Soil type – Silty Sand, SM • K = 0.9 cm/hr or 0.00025 cm/sec

  23. Comparison of Values k • We have k=0.00025 cm/sec • Silty Sand Soil = SM • Need Sieve analysis • County found k = 0.5 ft/day = 0.000176 cm/sec • How determined? • Soil from Boring 214 from 10 to 11.5’

  24. Comparison of Values k

  25. Comparison of Values k • We have k=0.00025 cm/sec • Silty Sand Soil = SM • Need Sieve analysis • County found k = 0.5 ft/day = 0.000176 cm/sec • Lab Test: Falling Head Permeameter • Soil:Poorly graded Sand = SP

  26. Unit Conversion Chart for k

  27. Tests We are Performing and Why • Moisture and Density • Foundation Recommendations • Slope Stability • Relative Compaction of Fill (Field Values)

  28. Tests We are Performing and Why • Sieve Analysis and Hydrometer • Classification • Correlation with Permeability Chart

  29. Tests We are Performing and Why • Direct Shear • Foundation Recommendations • Slope Stability

  30. Tests We are Performing and Why • Direct Shear • Foundation Recommendations • Slope Stability • This test is being performed in my lab

  31. Tests We are Performing and Why • Proctor Test (Max D.D. and Opt M.C.) • Relative Compaction of Fill (Laboratory standard) • Specifications for regrading

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