12 Retaining Walls TYPE OF RETAINING WALLS by
12. Retaining Walls TYPE OF RETAINING WALLS by Prof. Jae-Yeol Cho EARTH PRESSURE FOR COMMON LOADING STABILITY OF RETAINING WALLS 457. 306 Theory of Reinforced Concrete and Lab. II Fall 2009 -1 -
12. Retaining Walls TYPE OF RETAINING WALLS hold back masses of earth or other loose material. Continuous back drain, Crushed stone Tile drain Toe (a) Gravity wall Arm Crushed stone (b) Cantilever wall Heel Counterfort Weep hole (c) Counterfort wall Theory of Reinforced Concrete and Lab II. -2 - Fall 2009
12. Retaining Walls EARTH PRESSURE Q>What would happen if a wall is built in contact with a solid, such as rock? If a vertical wall retains soil, the earth pressure is (1) where : unit weight of soil : coefficient of earth pressure at rest (depends on soil type and compaction) 0. 4~0. 5 for uncompacted noncohesive soils. (sands, gravels) ~0. 8 for compacted sands and gravels. 0. 7~1. 0 for cohesive soil. Theory of Reinforced Concrete and Lab II. -3 - Fall 2009
12. Retaining Walls EARTH PRESSURE Sliding of Retaining Wall usually, walls move slightly under the action of the earth pressure. ( 1% of wall height ) Active earth pressure Sliding plane acts when the wall move away from the fill. Passive earth pressure acts when the wall is pushed against the fill. where is angle of internal friction is the coefficient of intergranular friction Theory of Reinforced Concrete and Lab II. -4 - Fall 2009
12. Retaining Walls EARTH PRESSURE Coefficient of Earth Pressure. According to Rankine, coefficient for active earth pressure is (2) coefficient for passive earth pressure is (3) where, is soil surface angle to the horizontal. Rankine’s theory is valid only for noncohesive soils. Theory of Reinforced Concrete and Lab II. -5 - Fall 2009
12. Retaining Walls EARTH PRESSURE Determination of Refer to SOIL MECHANICS! Theory of Reinforced Concrete and Lab II. -6 - Fall 2009
12. Retaining Walls EARTH PRESSURE FOR COMMON LOADING Conditions of Loading - horizontal surface of fill inclined surface of fill horizontal surface of fill carrying a uniformly distributed additional load Theory of Reinforced Concrete and Lab II. -7 - Fall 2009
12. Retaining Walls EARTH PRESSURE FOR COMMON LOADING Condition of Loading - the pressure of the soil ABOVE groundwater is determined as usual the pressure of the soil BELOW groundwater is the sum of water pressure and soil pressure (4, 5) Theory of Reinforced Concrete and Lab II. -8 - Fall 2009
12. Retaining Walls STABILITY OF RETAINING WALLS Failure Modes of Retaining Walls (1) Individual parts may not be strong enough to resist the acting forces. � should be designed according to KCI Code (usual load factors and strength reduction factors) (2) The wall as a whole may be bodily displaced by the earth pressure. (External Stability) � should be checked based on ACTUAL earth pressure and on service dead/live load Theory of Reinforced Concrete and Lab II. -9 - Fall 2009
12. Retaining Walls STABILITY OF RETAINING WALLS External Stability (1) Safety against sliding (6) where, f : coef. of friction : component of the total earth horizontal pressure P : vertical component of P In the figure R is total resultant and W is the weight of wall plus soil resisting on the footing. Theory of Reinforced Concrete and Lab II. -10 - Fall 2009
12. Retaining Walls STABILITY OF RETAINING WALLS External Stability (2) Safe against bearing stability The base plane ab, 1 m wide longitudinally, is subject to a normal force Rv, and to a moment about the centroid (l/2 – a)Rv Therefore, the following usual formula can be used (7) Theory of Reinforced Concrete and Lab II. -11 - Fall 2009
12. Retaining Walls (a) Resultant in middle third (b) Resultant at edge middle third (c) Resultant outside middle third Theory of Reinforced Concrete and Lab II. -12 - Fall 2009
12. Retaining Walls STABILITY OF RETAINING WALLS External Stability (3) Safe against overturning about the point b, (8) Resisting moment Overturning moment Theory of Reinforced Concrete and Lab II. -13 - Fall 2009
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