Counterfort Retaining Wall

It is a power point presentation on Counterfort Retaining wall.

1. Enrollment No . Name 130120106039 KAIZER DAVE 130120106045 KISHAN VYAS 130120106061 BINOY PATEL Internal Guide: Prof . Jay Sir Prof. Sandeep Sir 1 Gandhinagar Institute of Technology: Department of Civil Engineering Design of Reinforced concrete Structure ( 2170607 ) -COUNTERFORT RETAINING WALL GANDHINAGAR INSTITUTE OF TECHNOLOGY

2. RETAINING WALL A Retaining wall is a structure used to retain the earth or other materials and to maintain ground surface at different elevations on either side of it. Gandhinagar Institute of Technology : Department of Civil Engineering 2

3. RETAINING WALL TERMINOLOGY Gandhinagar Institute of Technology : Department of Civil Engineering 3

4. TYPES OF RETAINING WALLS Gandhinagar Institute of Technology : Department of Civil Engineering 4 Gravity retaining walls. Cantilever retaining walls. Counterfort retaining walls. Buttress wall. Bridge abutment. Box culvert.

5. Gandhinagar Institute of Technology : Department of Civil Engineering 5 Gravity retaining wall Cantilevered retaining wall Precast concrete retaining wall Precast concrete crib retaining wall Sheet pile wall

6. COUNTERFORT RETAINING WALL Gandhinagar Institute of Technology : Department of Civil Engineering 6 In the counterfort retaining wall, the stem and the base and the base slab are tied together by counterforts, at suitable intervals. Because of provision of counterforts, the vertical stem as well as the heel slab acts as a continuous slab, in contrast to the cantilevers of cantilever retaining wall. Counterfort retaining walls are economical for height over about 6m.

7. FORCES ACTING ON RETAINING WALL Lateral earth pressure Self weight of retaining wall Weight of soil above the base slab Surcharge, i.e. forces due to loads on earth surface. Soil reaction below base slab Frictional force at the bottom of base slab Gandhinagar Institute of Technology : Department of Civil Engineering 7

8. Earth Pressure (P) Earth pressure is the pressure exerted by the retaining material on the retaining wall. This pressure tends to deflect the wall outward. Types of earth pressure : Active earth pressure or earth pressure (Pa) and Passive earth pressure ( Pp ). Active earth pressure tends to deflect the wall away from the backfill. Gandhinagar Institute of Technology : Department of Civil Engineering 8

9. Factors affecting earth pressure Earth pressure depends on type of backfill, the height of wall and the soil conditions Soil conditions: The different soil conditions are • Dry or moist backfill with no surcharge • Submerged backfill • Backfill with uniform surcharge • Backfill with sloping surface •Inclined back and surcharge Gandhinagar Institute of Technology : Department of Civil Engineering 9

10. (1) Analysis for dry back fills with no surcharge Maximum pressure at any height, p=ka ϒ h Total pressure at any height from top,   Gandhinagar Institute of Technology : Department of Civil Engineering 10

11. = Coefficient of active earth pressure = ( 1-sin Φ )/(1+sin Φ )= Φ = 1/ , coefficient of passive earth pressure = Angle of internal friction or angle of repose ϒ =Unit weight or density of backfill   Gandhinagar Institute of Technology : Department of Civil Engineering 11

12. (2) Submerged backfill Lateral pressure due to submerged weight of soil = ϒ H Lateral pressure due to water, = H Total pressure at base, = ϒ H H   Gandhinagar Institute of Technology : Department of Civil Engineering 12

13. (3)Backfill with uniform surcharge The lateral pressure due to surcharge, = q • The lateral pressure due to backfill, = H • Lateral pressure intensity at base, q + H   Gandhinagar Institute of Technology : Department of Civil Engineering 13

14. (4) Backfill with sloping surface The total earth pressure acts at an angle β with horizontal. cos β β =angle of surcharge If surcharge is horizontal, β =0 Therefore,   Gandhinagar Institute of Technology : Department of Civil Engineering 14

15. (5) Inclined back and surcharge Resultant of pressure and weight of soil wedge W is calculated as P= where   Gandhinagar Institute of Technology : Department of Civil Engineering 15

16. Stability Conditions The retaining wall should satisfy the following stability condition- •Stability against overturning •Stability against sliding •Maximum pressure at base should not exceed safe bearing capacity of soil. Gandhinagar Institute of Technology : Department of Civil Engineering 16

17. Stability against overturning As per IS:456-2000, CI.20.1, factor of safety against overturning should not be less than 1.4.In case where dead load provides the restoring moment, only 0.9 times the characteristic dead load shall be considered. Hence ,the factor of safety is given by relation, F.S= ≥ 1.4 = ≥ 1.55   Gandhinagar Institute of Technology : Department of Civil Engineering 17

18. Stability against sliding As per IS:456-2000, CI.20.2, factor of safety against sliding should not be less than 1.4.In this case also 0.9 times characteristic dead load shall be taken into account. F.S = ≥ 1.4 = ≥ 1.4 = ≥ 1.55 Where,µ=coefficient of friction   Gandhinagar Institute of Technology : Department of Civil Engineering 18

19. Maximum pressure at base should not exceed safe bearing capacity of soil. The intensity of soil pressure at toe, ]……….at toe ]………..at heel • should not exceed safe bearing capacity(SBC) of soil. • For no tension , should not be negative.   Gandhinagar Institute of Technology : Department of Civil Engineering 19