Corporate 2 Template

RETAINING WALL

-EAT-352 (CONCRETE BUILDING DESIGN II)-

EAT 352 CONCRETE BUILDING DESIGN IIMOHD FAIZ BIN MOHAMMAD ZAKIwww.company.comwww.company.com1WHAT IS RETAINING WALL?.EAT 352 CONCRETE BUILDING DESIGN II

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CONCEPT OF RETAINING WALL.EAT 352 CONCRETE BUILDING DESIGN IITo retain earth or other material in a vertical or nearly vertical position at locations where an abrupt change in ground level occurswww.company.com3

PURPOSE OF RETAINING WALL.EAT 352 CONCRETE BUILDING DESIGN IITo stabilize the slopes and provide useful areas at different elevations.www.company.com4CONTEAT 352 CONCRETE BUILDING DESIGN II

stabilize the slopes for buildings, roads and railways.

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CONTEAT 352 CONCRETE BUILDING DESIGN IIRetaining wall prevents the retain earth from assuming its natural angle of repose.

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CONTEAT 352 CONCRETE BUILDING DESIGN IIThis caused the retained earth to exert a lateral pressure on the wall , thereby tending to overturn , slide and settle the retaining wall structure.

www.company.com7ServiceabilityCONTEAT 352 CONCRETE BUILDING DESIGN IIThe wall must designed to be stable under the effects of the lateral pressure, and also to satisfy

Usual requirements of strengthwww.company.com8TYPES OF RETAINING WALLSConcrete retaining wall may be considered in three basic categories :

GRAVITY WALLCOUNTERFORT WALLCOUNTERFORT WALL

EAT 352 CONCRETE BUILDING DESIGN IIwww.company.com9GRAVITY WALLGravity 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

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COUNTERFORT WALLUsed 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 IIwww.company.com11CANTILEVER WALL.EAT 352 CONCRETE BUILDING DESIGN II

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www.company.com13CONT.EAT 352 CONCRETE BUILDING DESIGN II

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the economic height range up to 6.0 m; if exceed this height , more economic to use pre-stressing techniqueswww.company.com15CONTEAT 352 CONCRETE BUILDING DESIGN II

The stability of the wall is maintained by the

-weight of soil on the base slab plus

-self weight of structure.www.company.com16SURCHARGE.EAT 352 CONCRETE BUILDING DESIGN II

www.company.com17ANALYSIS AND DESIGNThe design of retaining wall divided into two fundamental stages

Stability analysisElement design and detailingEAT 352 CONCRETE BUILDING DESIGN IIwww.company.com18STABILITY ANALYSISTHREE 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 IIwww.company.com19Partial safety factor at the ultimate limit stateEAT 352 CONCRETE BUILDING DESIGN II

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OVERTURNINGThis 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.

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CONTA 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.

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CONTThe 'unfavourable' effects of the variable surcharge loading, if any, are multiplied by a partial safety factor of 1.5.

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SLIDINGThe 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 IIwww.company.com24SLIDINGA partial safety factor of f = 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 f = 1.35 and 1.5 respectively. EAT 352 CONCRETE BUILDING DESIGN II

www.company.com25SETTLEMENTThe 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 IIwww.company.com26

CONTThe 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

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ELEMENT DESIGN AND DETAILINGthe 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 IIwww.company.com28

CONTThe stem is designed to resist the moment caused by the force f Hf, with f 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 IIwww.company.com29CONTIn 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.

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www.company.com30CONTThe 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

www.company.com31CONTTwo 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 IIwww.company.com32