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Stress of soil

CHAPTER 3. Stress of soil. §3 Stress of soil. § 3.1 General § 3.2 Self-weight stress § 3.3 Stress at the bottom of foundation § 3.4 Additional stress in foundation. §3 Stress of soil. §3.1 General. Weight of soil (effective stress) Surface loads Fill large area Point loads:

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Stress of soil

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  1. CHAPTER 3 Stress of soil

  2. §3 Stress of soil §3.1 General §3.2 Self-weight stress §3.3 Stress at the bottom of foundation §3.4 Additional stress in foundation

  3. §3 Stress of soil §3.1 General • Weight of soil (effective stress) • Surface loads • Fill large area • Point loads: • Hydro pole, light stand, column, etc • Lines loads • Rack or rail loading, strip foundation • Rectangular area • Raft or rectangular footing • Circular area • Tank • Earth embankment • Road, railway, fill, ice, etc.

  4. σcz natural ground σcz= z z z 1 1 §3 Stress of soil §3.2 Self-weight stress • Due to soil’s self weight

  5. natural ground h1 1 h2 2 ground water level 3 h3 1 h1 1 h1 +  2h2 1 h1 +  2h2 + 3h3

  6. natural ground z  lateral earth pressure coefficient at rest • Assumption： • no shear stresses on the vertical planes bounding the column in horizontal direction.

  7. Example 1: • How to calculate the stress in soils? Natural ground Clay Ground water level sand Top roof of the aquitard

  8. 57.0kPa 80.1kPa 103.1kPa 150.1kPa 194.1kPa • Solution: Natural ground Clay Ground water level sand Top roof of the aquitard

  9. F §3 Stress of soil §3.3Stress at the bottom of foundation Filled soil Smaller load Smaller load Geotextile polymer Extreme load Extreme load Base pressure

  10. Outdoor ground

  11. pmax pmin=0 pmin=0 pmax e<l/6 e=l/6 pmin<0 pmin pmax redistribution of the base pressure pmax e>l/6 Discussion：

  12. P o x r y x R z y z §3 Stress of soil §3.4 Additional stress in foundation (1) Point load q M(x,y,0) M(x,y,z) • Note: • z is independent of • elastic modulus • Poisson’s ratio.

  13. Stresses due to point load Rules of the stress distribution

  14. Pa Pb z a b several point loads: superposition principle

  15. (2) Strip area carrying uniform pressure

  16. III II o o IV I z M III II IV I

  17. II o o o o IV III I I II

  18. o o III IV II I

  19. (3) Strip area carrying linearly increasing pressure

  20. F 0.1m M 1.5m 0＝18.5kN/m3 2m • Example 2 • Strifoundation • Load :F=400kN/m，M=20kN•m， ? Additional stress on the middle of base ? Plot the distribution of the stress

  21. F=400kN/m M=20kN •m 0＝18.5kN/m3 0.1m 319.7kPa 140.3kPa 1.5m 2m Solution 1.Base pressure

  22. F=400kN/m M=20kN •m 0＝18.5kN/m3 1.5m 1.5m 0.1m 292.0kPa 112.6kPa 2m 2.Additonal pressure

  23. F=400kN/m M=20kN •m 0＝18.5kN/m3 0.1m 112.6kPa 292.0kPa 112.6kPa 1.5m 179.4kPa 2m 3.Additioanl pressure at the middle point

  24. F=400kN/m M=20kN •m 0＝18.5kN/m3 1.5m 0.1m 202.2kPa 1m 193.7kPa 1m 165.7kPa 2m 111.2kPa 2m 80.9kPa 2m 62.3kPa 2m result

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