RETAINING WALL -EAT-352 (CONCRETE BUILDING DESIGN II)-

1. RETAINING WALL-EAT-352 (CONCRETE BUILDING DESIGN II)- MOHD FAIZ BIN MOHAMMAD ZAKI EAT 352 CONCRETE BUILDING DESIGN II

2. WHAT IS RETAINING WALL? • . EAT 352 CONCRETE BUILDING DESIGN II

3. CONCEPT OF RETAINING WALL • . To retain earth or other material in a vertical or nearly vertical position at locations where an abrupt change in ground level occurs EAT 352 CONCRETE BUILDING DESIGN II

4. PURPOSE OF RETAINING WALL • . To stabilize the slopes and provide useful areas at different elevations. EAT 352 CONCRETE BUILDING DESIGN II

5. CONT… stabilize the slopes for buildings, roads and railways. EAT 352 CONCRETE BUILDING DESIGN II

6. CONT… Retaining wall prevents the retain earth from assuming its natural angle of repose. EAT 352 CONCRETE BUILDING DESIGN II

7. CONT… This caused the retained earth to exert a lateral pressure on the wall , thereby tending to overturn , slide and settle the retaining wall structure. EAT 352 CONCRETE BUILDING DESIGN II

8. CONT… The wall must designed to be stable under the effects of the lateral pressure, and also to satisfy Usual requirements of strength Serviceability EAT 352 CONCRETE BUILDING DESIGN II

9. TYPES OF RETAINING WALLS • Concrete retaining wall may be considered in three basic categories : • GRAVITY WALL • COUNTERFORT WALL • COUNTERFORT WALL EAT 352 CONCRETE BUILDING DESIGN II

10. GRAVITY WALL • Gravity walls depend on their mass (stone, concrete or other heavy material) to resist pressure from behind. Its usually constructed of plain concrete or stone masonry. EAT 352 CONCRETE BUILDING DESIGN II

11. COUNTERFORT WALL • Used where overall height of wall is to large to be constructed economically as a cantilever. • They consist of the wall and footing of cantilever retaining walls, with the addition of structural supports that tied at interval by counterforts or bracing walls. The function is to increase the resistance to the pressure from the weight of the soil. EAT 352 CONCRETE BUILDING DESIGN II

12. CANTILEVER WALL • . EAT 352 CONCRETE BUILDING DESIGN II

13. CONT… EAT 352 CONCRETE BUILDING DESIGN II

14. CONT… • . EAT 352 CONCRETE BUILDING DESIGN II

15. CONT… the economic height range up to 6.0 m; if exceed this height , more economic to use pre-stressing techniques EAT 352 CONCRETE BUILDING DESIGN II

16. CONT… The stability of the wall is maintained by the -weight of soil on the base slab plus -self weight of structure. EAT 352 CONCRETE BUILDING DESIGN II

17. SURCHARGE • . EAT 352 CONCRETE BUILDING DESIGN II

18. ANALYSIS AND DESIGN • The design of retaining wall divided into two fundamental stages • Stability analysis • Element design and detailing EAT 352 CONCRETE BUILDING DESIGN II

19. STABILITY ANALYSIS • THREE SETS OF LOAD COMBINATIONS must be considered at the ultimate limit state. The first two combinations will be used for consideration of both structural failure , (STR), and geotechnical failure, (GEO). • The third combination consider the possible loss of equilibrium (EQU) of the structure such as overturning. The partial safety factors to be used for these three combinations. EAT 352 CONCRETE BUILDING DESIGN II

20. Partial safety factor at the ultimate limit state EAT 352 CONCRETE BUILDING DESIGN II

21. OVERTURNING • This occurs because of unbalanced moments and when overturning moment about toe due to lateral pressure is larger than the resisting moment due to the weights of wall and weight of soil above the heel slab. The critical conditions are when maximum horizontal force acts with a minimum vertical load. EAT 352 CONCRETE BUILDING DESIGN II

22. CONT… • A partial safety factor of 0.9 is applied to the permanent vertical load ∑Vk (weight of wall + weight of soil) if its effect is ‘favourable'. The 'unfavourable' effects of the permanent earth pressure loading Hk at the rear face of the wall are multiplied by a partial safety factor of 1.1. EAT 352 CONCRETE BUILDING DESIGN II

23. CONT… • The 'unfavourable' effects of the variable surcharge loading, if any, are multiplied by a partial safety factor of 1.5. EAT 352 CONCRETE BUILDING DESIGN II

24. SLIDING • The resistance against sliding is essentially provided by the friction between the bottom surface of the base slab and the soil beneath it. • Resistance provided by the passive earth pressure on the front face of the base may make some contribution, but since this material is often backfilled against the face, its resistance cannot be guaranteed and is usually ignored. EAT 352 CONCRETE BUILDING DESIGN II

25. SLIDING • A partial safety factor of γf = 1.0 is applied to the permanent vertical load ∑Vk, if its effect is 'favourable' (i.e. contribute to the sliding resistance) and the 'unfavourable’ effects of the permanent earth and surcharge pressures at the rear face of the wall are multiplied by partial safety factor of γf = 1.35 and 1.5 respectively. EAT 352 CONCRETE BUILDING DESIGN II

26. SETTLEMENT • The width of the base slab must be adequate to distribute the vertical force to the foundation soil without causing excessive settlement or rotation. • To determine the required size of the base the bearing pressure underneath it is assessed on the basis of the ultimate limit state (GEO). • Since the base slab of the wall is subjected to the combined effects of an eccentric vertical load coupled with an overturning moment, the analysis is similar to that for foundation design. EAT 352 CONCRETE BUILDING DESIGN II

27. CONT… • The distribution of bearing pressure will be as shown in the figure provided the effective eccentricity e lies within the middle third of the base. The bearing pressure is then given by, EAT 352 CONCRETE BUILDING DESIGN II

28. ELEMENT DESIGN AND DETAILING • the retaining wall , i.e. stem , toe slab and heel slab are designed as cantilever slabs to resist the designed moments and shear forces. EAT 352 CONCRETE BUILDING DESIGN II

29. CONT… • The stem is designed to resist the moment caused by the force γf Hf, with γf values taken for load combination 1 if this load combination is deemed to be critical. • The flexural reinforcement is provided near the rear face of the stem, and my be curtailed in stages for economy. EAT 352 CONCRETE BUILDING DESIGN II

30. CONT… • In the case of toe slab, the net pressure is obtained by deducting the weight of the concrete in the toe slab from the upward acting soil pressure. • The net pressure acts upward and the flexural reinforcement has to be provided at the bottom of toe slab. EAT 352 CONCRETE BUILDING DESIGN II

31. CONT… • The heel slab must be designed to resist the moment due to downward pressure from the weight of the retained earth (plus surchage, if any) and concrete slab. • Since the net pressure acts downward, • the flexural reinforcement is • provided at the top of the heel • slab. EAT 352 CONCRETE BUILDING DESIGN II

32. CONT… • Two sets of load combinations must be considered at the ultimate limit state . For load combination 1, the moment due to the horizontal load on the maximum bearing pressure at the toe of the wall is 'unfavourable' whilst the moments of the weight of the wall and the earth acting on the heel of the wall act in the opposite sense and are thus ' favourable' . • Hence the partial safety factor for the lateral earth pressure and lateral surcharge are 1.35 and 1.5 respectively. EAT 352 CONCRETE BUILDING DESIGN II