A. Differentiate Coulomb’s and Rankine’s Theories B. Collect the data of at least 5 retaining walls constructed in Pakistan. The details should include the following information. 1. Type and purpose of the wall 2. Technical specification 3. Materials used 4. Current status (Stable/maintained/upgraded) 5. location with photographic evidence 6. your suggestions for improvement or comments on the flaws if exist.

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A. Rankine’s Earth Pressure Theory.

The Rankine’s theory assumes that there is no wall friction (δ=0) , the ground and failure surfaces are straight planes, and that the resultant force acts parallel to the backfill slope.

Rankine’s Theory At Rest Earth Pressure:

The at-rest earth pressure coefficient (Ko) is applicable for determining the active pressure in clays for strutted systems. Because of the cohesive property of clay there will be no lateral pressure exerted in the at-rest condition up to some height at the time the excavation is made.creep and swelling of the clay will occur and a lateral pressure will develop. This coefficient takes the characteristics of clay into account and will always give a positive lateral pressure.

Coulomb’s Wedge Theory:

The Coulomb theory provides a method of analysis that gives the resultant horizontal force on a retaining system for any slope of wall, wall friction, and slope of backfill provided. This theory is based on the assumption that soil shear resistance develops along the wall and failure plane. The following coefficient is for resultant pressure acting at angle. Since wall friction requires a curved surface of sliding to satisfy equilibrium, the Coulomb formula will give only approximate results as it assumes planar failure surfaces. The accuracy for Coulomb wil1 diminish with increased depth For passive pressures the Coulomb formula can also give inaccurate results when there is a large back slope or wall friction angle. These conditions should be investigated and an increased factor of safety considered.

B. Gravity retaining wall :

  • Gravity retaining wall depends on its self weight only to resist lateral earth pressure.Gravity retaining wall depends on its self weight only to resist lateral earth pressure. Commonly, gravity retaining wall is massive because it requires significant gravity load to counter act soil pressure.
  • It can be constructed from different materials such as concrete, stone, and masonry units.
  • It is stable retaining wall.

Gabion Retaining Walls:

  • Gabion retaining wall walls are multi-celled, rectangular wire mesh boxes, which are filled with rocks or other suitable materials.Gabion retaining wall walls are multi-celled, rectangular wire mesh boxes, which are filled with rocks or other suitable materials.
  • It is employed for construction of erosion control structures.
  • It is also used to stabilize steep slopes.

Cantilever Retaining Wall:

  • Cantilever retaining wall composed of stem and base slab
  • It is constructed from reinforced concrete, precast concrete, or prestress concrete.
  • sliding, overturning, and bearing pressure shall be taken into consideration during its design.
  • It is stable retaining wall.

Counter-fort / Buttressed Retaining Wall:

  • It is a cantilever retaining wall but strengthened with counter forts monolithic with the back of the wall slab and base slab.
  • Counter fort spacing is equal or slightly larger than half of the counter-fort height.
  • It is stable retaining wall

Anchored Retaining Wall

  • This type of retaining wall is employed when the space is limited or thin retaining wall is required.
  • Anchored retaining wall is suitable for loose soil over rocks.
  • Considerably high retaining wall can be constructed using this type of retaining wall structure system.
  • It is also stable retaining wall .