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Earth retaining 2

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  • 1. TOPIC 4 : LATERAL EARTHPRESSURE EARTH RETAINING STRUCTURES MARLIZA ASHIQIN BT KHAZALI
  • 2. COURSE LEARNINGOUTCOME• CLO 1 : Explain clearly the principle and concept of geotechnical engineering (C4)• CLO 2 : Solve problems in soil stability using appropriate method (C4)
  • 3. LATERAL EARTH PRESSURE Types of Retaining Wall 2.4.1 Gravity Walls 2.4.2 Embedded walls 2.4.3 Reinforced and anchored earth
  • 4. LATERAL EARTH PRESSURE Gravity Walls 2.4.1 Gravity Walls Masonry walls Gabion walls Crib walls RC walls Counterfort walls Buttressed walls
  • 5. LATERAL EARTH PRESSURE Gravity Walls Unreinforced masonry wall
  • 6. LATERAL EARTH PRESSURE Gravity Walls Gabion wall
  • 7. LATERAL EARTH PRESSURE Gravity Walls Crib wall
  • 8. LATERAL EARTH PRESSURE Gravity Walls Types of RC Gravity Walls
  • 9. LATERAL EARTH PRESSURE Embedded Walls 2.4.2 Embedded walls Driven sheet-pile walls Braced or propped walls Contiguous bored-pile walls Secant bored-pile walls Diaphram walls
  • 10. LATERAL EARTH PRESSURE Embedded Walls Types of embedded walls
  • 11. LATERAL EARTH PRESSURE Reinforced and Anchored Earth 2.4.3 Reinforced and anchored earth Reinforced earth wall Soil nailing Ground anchors
  • 12. LATERAL EARTH PRESSURE Reinforced and anchored earth Reinforced earth and soil nailing
  • 13. LATERAL EARTH PRESSURE Stability Criteria 2.5 Stability of Rigid Walls Failures of the rigid gravity wall may occur due to any of the followings:  Overturning failure  Sliding failure  Bearing capacity failure In designing the structures at least the first three of the design criteria must be analysed and satisfied.
  • 14. LATERAL EARTH PRESSURE Stability CriteriaThe stability of the retaining wall should be checked against : (i) FOS against overturning (recommended FOS = 2.0) Resisting moment FOS = Disturbing moment (ii) FOS against sliding (recommended FOS = 2.0) RV tan δ + (0.5 - 0.7) Pp + cw B FOS = RH
  • 15. LATERAL EARTH PRESSURE Stability AnalysisThe stability of the retaining wall shouldbe checked against : 2.3.1 FOS against overturning (recommended FOS = 2.0) Resisting moment FOS = Disturbing moment ∑V Ph Pp .. overturning about A A
  • 16. LATERAL EARTH PRESSURE Stability Criteria2.3.2 FOS against sliding (recommended FOS = 2.0) RV tan δ + (0.5 - 0.7) Pp + cw BFOS = RH ∑V Ph Pp Friction & wall base adhesion
  • 17. LATERAL EARTH PRESSURE Stability Criteria 2.3.3 For base pressure (to be compared against the bearing capacity of the founding soil. Recommended FOS = 3.0) RV  6e  qb = 1 +  B  B Now, Lever arm of base resultant ∑ Moment x= RV B Thus eccentricity e = - x 2
  • 18. LATERAL EARTH PRESSURE Stability Analysis ∑V Ph Pp Base pressure on the founding soil
  • 19. LATERAL EARTH PRESSURE Stability Analysis Worked example : Figure below shows the cross-section of a reinforced concrete retaining structure. The retained soil behind the structure and the soil in front of it are cohesionless and has the following properties: SOIL 1 : φu = 35o, γd = 17 kN/m3, SOIL 2 : φu = 30o, δ = 25o , γd = 18 kN/m3, γsat = 20 kN/m3 The unit weight of concrete is 24 kN/m3. Taking into account the passive resistance in front of the wall, determine a minimum value for the width of the wall to satisfy the following design criteria: Factor of safety against overturning > 2.5 Factor of safety against sliding > 1.5 Maximum base pressure should not exceed 150 kPa
  • 20. LATERAL EARTH PRESSURE Stability Analysis THE PROBLEM 30 kN/m2 0.5 m SOIL 1 2.0 m 4.0 m GWT SOIL 2 2.9 m SOIL 2 0.6 m 4.5 m 2.0 m
  • 21. LATERAL EARTH PRESSURE Stability Analysis 30 kN/m2THE SOLUTION 0.5 m SOIL 1 W1 2.0 m P1 P3 W3 GWT 4.0 m SOIL 2 W41 2.9 m W2 P2 P4 SOIL 2 PP P5 P6 0.6 m 4.5 m 2.0 m
  • 22. LATERAL EARTH PRESSURE Stability AnalysisDetermination of the Earth Pressure Coefficients 1 − sin φ 1 - sin 35 o K a1 = = = 0.271 1 + sin φ 1 + sin 35 o 1 − sin φ 1 - sin 30 o K a2 = = = 0.333 1 + sin φ 1 + sin 30 o 1 + sin φ 1 + sin 30 o K p2 = = = 3.00 1 − sin φ 1 − sin 30 o
  • 23. LATERAL EARTH PRESSURE Stability Analysis
  • 24. LATERAL EARTH PRESSURE Stability AnalysisTo check for stability of the retaining wall(i) FOS against overturning > 2.5 Resisting moment 1288.55 FOS = = = 3.83 > 2.5, thus it is OK Disturbing moment 336.50(ii) FOS against sliding > 1.5 RV tan δ + 0.5 Pp 452.9 tan 25 o + 0.5 x 60.75 FOS = = = 1.34 < 1.5 RH 180.94 Thus it is not OK
  • 25. LATERAL EARTH PRESSURE Stability Analysis (iii) For base pressure RV  6e  qb = 1 +  B  B Now, Lever arm of base resultant ∑ Moment 1288.55 - 336.5 x= = = 2.10 RV 452.9 B Thus eccentricity e = - x = 2.25 - 2.10 = 0.15 2 452.9  6 x 0.15  Therefore qb = 1 +  4.5  4.5 
  • 26. LATERAL EARTH PRESSURE Stability Analysis qb = 120.8 and 80.5 kPa Since maximum base pressure is less than the bearing pressure of the soil, the foundation is stable against base pressure failure. DISTRIBUTION OF BASE PRESSURE 80.5 kPa 120.8 kPa In conclusion the retaining wall is not safe against sliding. To overcome this the width of the base may be increased or a key constructed at the toe.

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