Lateral earthpressures by sivakugan

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Geotechnical applications
K0, active & passive states
Rankine’s earth pressure theory
Design of retaining walls
A Mini Quiz
In geotechnical engineering, it is often necessary to prevent lateral soil movements.

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Lateral earthpressures by sivakugan

  1. 1. www.sci-geoteknik.blogspot.com<br />Lateral Earth Pressures<br />N. Sivakugan<br />Duration: 18 min<br />
  2. 2. 2<br />Contents<br />Geotechnical applications<br />K0, active & passive states<br />Rankine’s earth pressure theory<br />A 2-minute break<br /><ul><li>Design of retaining walls
  3. 3. A Mini Quiz</li></li></ul><li>3<br />Lateral Support<br />Tie rod<br />Anchor<br />Sheet pile<br />In geotechnical engineering, it is often necessary to prevent lateral soil movements. <br />Cantilever retaining wall<br />Braced excavation<br />Anchored sheet pile<br />
  4. 4. 4<br />Lateral Support<br />We have to estimate the lateral soil pressures acting on these structures, to be able to design them. <br />Soil nailing<br />Gravity Retaining wall<br />Reinforced earth wall<br />
  5. 5. 5<br />Soil Nailing<br />
  6. 6. 6<br />Sheet Pile<br />Sheet piles marked for driving<br />
  7. 7. 7<br />Sheet Pile<br />Sheet pile wall<br />
  8. 8. 8<br />Sheet Pile<br />Sheet pile wall<br />During installation<br />
  9. 9. 9<br />Lateral Support<br />geosynthetics<br />Reinforced earth walls are increasingly becoming popular.<br />
  10. 10. 10<br />Lateral Support<br />filled with soil<br />Crib walls have been used in Queensland.<br />Good drainage & allow plant growth.<br />Looks good.<br />Interlocking stretchers and headers<br />
  11. 11. 11<br />Earth Pressure at Rest <br />GL<br />v’<br />h’<br />In a homogeneous natural soil deposit,<br />X<br />the ratio h’/v’ is a constant known as coefficient of earth pressure at rest (K0).<br />Importantly, at K0 state, there are no lateral strains.<br />
  12. 12. 12<br />Estimating K0<br />Poisson’s ratio<br />For normally consolidated clays and granular soils, <br />K0 = 1 – sin ’<br />For overconsolidated clays, <br />K0,overconsolidated = K0,normally consolidated OCR0.5<br />From elastic analysis, <br />
  13. 13. 13<br />Active/Passive Earth Pressures<br />- in granular soils<br />Wall moves away from soil<br />Wall moves towards soil<br />A<br />B<br />smooth wall<br />Let’s look at the soil elements A and B during the wall movement. <br />
  14. 14. 14<br />v’<br />z<br />h’<br />A<br />Active Earth Pressure<br />- in granular soils<br />v’ = z<br /> Initially, there is no lateral movement. <br />h’ = K0 v’ = K0 z<br /> As the wall moves away from the soil, <br />v’ remains the same; and<br />h’ decreases till failure occurs.<br />Active state<br />
  15. 15. 15<br /><br />failure envelope<br />Initially (K0 state)<br />Failure (Active state)<br /><br />decreasing h’<br />Active Earth Pressure<br />- in granular soils<br /> As the wall moves away from the soil, <br />v’<br />active earth pressure<br />
  16. 16. 16<br /><br />failure envelope<br />WJM Rankine<br />(1820-1872)<br /><br /><br />Active Earth Pressure<br />- in granular soils<br />v’<br />[h’]active<br />Rankine’s coefficient of active earth pressure<br />
  17. 17. 17<br /><br />v’<br />A<br />45 + /2<br />h’<br />failure envelope<br />90+<br /><br /><br />Active Earth Pressure<br />- in granular soils<br />Failure plane is at <br />45 + /2 to horizontal<br />v’<br />[h’]active<br />
  18. 18. 18<br />v’<br />z<br />h’<br />A<br />h’<br />K0 state<br />Active state<br />wall movement<br />Active Earth Pressure<br />- in granular soils<br /> As the wall moves away from the soil, <br />h’ decreases till failure occurs.<br />
  19. 19. 19<br />Macquorn Rankine<br />
  20. 20. 20<br />Active Earth Pressure<br />- in cohesive soils<br />Follow the same steps as for granular soils. Only difference is that c  0.<br />Everything else the same as for granular soils.<br />
  21. 21. 21<br />v’<br />B<br />h’<br />Passive Earth Pressure<br />- in granular soils<br />Initially, soil is in K0 state.<br /> As the wall moves towards the soil, <br />v’ remains the same, and<br />h’ increases till failure occurs.<br />Passive state<br />
  22. 22. 22<br /><br />failure envelope<br />Initially (K0 state)<br />Failure (Active state)<br /><br />increasing h’<br />Passive Earth Pressure<br />- in granular soils<br /> As the wall moves towards the soil, <br />passive earth pressure<br />v’<br />
  23. 23. 23<br /><br />failure envelope<br /><br /><br />Passive Earth Pressure<br />- in granular soils<br />v’<br />[h’]passive<br />Rankine’s coefficient of passive earth pressure<br />
  24. 24. 24<br /><br />v’<br />A<br />45 - /2<br />h’<br />failure envelope<br />90+<br /><br /><br />Passive Earth Pressure<br />- in granular soils<br />Failure plane is at <br />45 - /2 to horizontal<br />[h’]passive<br />v’<br />
  25. 25. 25<br />v’<br />B<br />h’<br />h’<br />Passive state<br />K0 state<br />wall movement<br />Passive Earth Pressure<br />- in granular soils<br /> As the wall moves towards the soil, <br />h’ increases till failure occurs.<br />
  26. 26. 26<br />Passive Earth Pressure<br />- in cohesive soils<br />Follow the same steps as for granular soils. Only difference is that c  0.<br />Everything else the same as for granular soils.<br />
  27. 27. 27<br />H<br />PA=0.5 KAH2<br />h<br />PP=0.5 KPh2<br />Earth Pressure Distribution<br />- in granular soils<br />[h’]active<br />PA and PP are the resultant active and passive thrusts on the wall<br />[h’]passive<br />KAH<br />KPh<br />
  28. 28. h’<br />Passive state<br />Active state<br />K0 state<br />Wall movement (not to scale)<br />
  29. 29. 29<br />
  30. 30. 30<br />Macquorn Rankine<br />
  31. 31. 31<br />Rankine’s Earth Pressure Theory<br /><ul><li> Assumes smooth wall
  32. 32. Applicable only on vertical walls</li></li></ul><li>32<br />Retaining Walls- Applications<br />Road<br />Train<br />
  33. 33. 33<br />Retaining Walls- Applications<br />highway<br />
  34. 34. 34<br />Retaining Walls- Applications<br />basement wall<br />High-rise building<br />
  35. 35. 35<br />Gravity Retaining Walls<br />cement mortar<br />plain concrete or stone masonry<br />cobbles<br />They rely on their self weight to support the backfill<br />
  36. 36. 36<br />Cantilever Retaining Walls<br />Reinforced; smaller section than gravity walls<br />They act like vertical cantilever, fixed to the ground<br />
  37. 37. 37<br />2<br />2<br />Block no.<br />3<br />3<br />1<br />1<br />toe<br />toe<br />Analyse the stability of this rigid body with vertical walls (Rankine theory valid)<br />Design of Retaining Wall<br />- in granular soils<br />Wi = weight of block i<br />xi = horizontal distance of centroid of block i from toe<br />
  38. 38. soil-concrete friction angle  0.5 – 0.7 <br />2<br />2<br />PA<br />H<br />3<br />PA<br />3<br />1<br />PP<br />1<br />S<br />PP<br />h<br />S<br />toe<br />R<br />toe<br />R<br />y<br />y<br />Safety against sliding along the base<br />to be greater than 1.5<br />PP= 0.5 KPh2<br />PA= 0.5 KAH2<br />
  39. 39. 2<br />2<br />PA<br />H<br />3<br />PA<br />3<br />1<br />PP<br />1<br />S<br />PP<br />h<br />S<br />toe<br />R<br />toe<br />R<br />y<br />y<br />Safety against overturning about toe<br />to be greater than 2.0<br />
  40. 40. 40<br />Points to Ponder<br />How does the key help in improving the stability against sliding?<br />Shouldn’t we design retaining walls to resist at-rest (than active) earth pressures since the thrust on the wall is greater in K0 state (K0 > KA)?<br />

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