Retaining walls

General Information of Retaining Walls about its type, design and functionality; This file does not comprise of detail study of the Retaining Walls but for a startup it may help students!!!

1. Retaining Walls General Information

2. What are Retaining Walls and what is the purpose for having them? Retaining wall  is a structure that holds or retains soil behind it. There are many types of materials that can be used to create  retaining walls  like concrete blocks, poured concrete, treated timbers, rocks or boulders. Some are easy to use, others have a shorter life span, but all can retain soil. Retaining walls are used for maintaining the ground surfaces at different elevations on either side of it. Retaining walls provide lateral support to vertical slopes of soil. They retain  soil which would otherwise collapse into a more natural shape. The retained soil is referred to as backfill . Schematic Diagram of a Typical Retaining wall Few examples of beautiful use we can make of retaining walls functionally as well as aesthetically as shown in img 1 and 2 1 2

3. Types of Retaining walls: Typical Retaining wall diagram with all its necessary parts   Types of Retaining Walls An earth retaining structure can be considered to have the following types: Gravity Walls 1. Reinforced Gravity Walls Concrete Cantilever retaining wall Piling retaining wall Anchored retaining wall 2.Brick Masonry retaining walls 3.Stone Stone masonry retaining wall which are also used as bund walls Brick retaining walls used for retaining earth as well as landscaping.

4. Reinforced Concrete Retaining Walls: Gravity Retaining Walls It is that type of retaining wall that relies on their huge weight to retain the material behind it and achieve stability against failures. Gravity Retaining Wall can be constructed from concrete, stone or even brick masonry. Gravity retaining walls are much thicker in section. Geometry of these walls also help them to maintain the stability. Mass concrete walls are suitable for retained heights of up to 3 m. The cross section shape of the wall is affected by stability, the use of space in front of the wall, the required wall appearance and the method of construction.

5. Forces subjected to Retaining walls: Lateral forces : Earth pressure due to backfill and surcharge. Vertical forces: Acting downwards : 1.Self weight of the retaining wall ; 2.Weight of soil above heel slab. Acting upwards : 1.Force due to soil pressure underneath the base slab.

6. What is Earth pressure and how does it effect Retaining walls? 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) Passive earth pressure (Pp). Active earth pressure tends to deflect the wall away from the backfill. Passive earth pressure is the highest limiting lateral pressure developed at the onset of shear failure by wall moving in the direction opposite to the direction of acting earth pressure P a GL Variation of Earth pressure

7. Preliminary Dimensions for the construction of Retaining Walls: The tentative proportions of the parts of retaining wall may be obtained based on experience and optimization studies. Set the preliminary dimensions of retaining wall Base width, b = 0.48H to 0.56H Toe projection = 0.3 b Thickness of base slab = Thickness of stem = H/12 Top width of stem = 150 mm to 300 mm

8. Stability of Retaining walls: A retaining wall must be stable as a whole, and it must have sufficient strength to resist the forces acting on it. In order that the wall may be stable, the following conditions should be satisfied: The wall must be strong enough to resist the bending moment and shear force. The wall should not overturn. Maximum pressure at base should not exceed the SBC of soil. The wall should not slide due to lateral pressure. Inorder to ensure the stability of retaining walls there are necessary checks and special attention is given towards the design of the parts of the retaining walls, Following are the different checks to ensure stability of retaining walls and avoid failure of them as well. Check for Overturning. Check for Sliding. Check for Soil pressure.

9. Necessary Precautions for the Stability of Retaining Walls: Check for Over Turning: The lateral loads (earth pressure) causes overturning moment (M o ) about the toe. The weight of backfill, surcharge, self weight of retaining wall cause stabilizing moment ( M s ) about the toe. The factor of safety against overturning is given by ; ( Fos ) o = M s /M o The factor of safety should not be less than 1.4. As per IS 456-2000 recommendations, only 0.9 times the characteristic dead load shall be considered ( Fos ) o = 0.9M s /M o Check for Sliding: The lateral earth pressure on stem tries to slide the retaining wall away from back fill. This lateral force is resisted by frictional force between base slab and the soil below it. Maximum frictional force is given by: F = µ Σ W (where, Σ W is the total downward load.) If P H is the total horizontal pressure, then factor of safety against sliding is given by ( Fos ) s = µ Σ W/P H As per IS 456-2000 recommendations, the factor of safety should not less than 1.4 and only 0.9 times characteristic dead load is to be considered i.e ; ( Fos ) s = 0.9µ Σ W/P H

10. Necessary Precautions for the Stability of Retaining Walls: Check for Soil Pressure: The soil pressure varies linearly with more pressure on toe and less pressure on the end of heel. P1 ( max. ) < SBC of soil. P2( min.) > 0. Other Common Failures in Retaining walls are mentioned below:

11. Construction details of Retaining walls: Cantilever Retaining Wall Sections with Reinforcements: We can clearly notice now the main reinforcements are laid at the sides where the walls are subjected to the Earth pressures since tension zones are created in those parts

12. Construction details of Retaining walls: Counterfort Retaining Walls: Can be constructed of reinforced or prestressed concrete Suitable for over 4.5 m Triangular beams placed at suitable centres behind the stem and above the base to enable the stem and base to act as slab spanning horizontally over or under the counterforts

13. Precast Retaining Walls: Manufactured from high-grade pre cast concrete on the cantilever principle. Can be erected on a foundation as permanent retaining wall or be free standing to act as dividing wall between heaped materials which it can increase three times the storage volume for any given area Other advantages- reduction in time by eliminating curing period, cost of formwork, time to erect and dismantle the temporary forms Lifting holes are provided which can be utilized for fixing if required

14. Actual Site Images of Retaining walls: Retaining wall construction on-site images. Ref image-3,4,5 3 4 5 6 7 Precast Retaining walls The Members of the retaining walls are available readymade and we can use them as per our design requirements and convenience. Ref image-6,7

15. Case study: Shraddha Vivanta Residency L ake road, Bhandup (west), Mumbai 400 078

16. Location of the site and its scale: The name of this project is Shraddha Vivanta Residency and the construction work has started commencing 4 months ago. This project is undertaken by Vivanta Group and it’s a Residential Building near Lake Road, Bhandup (West) Location of the site and the area: 1300 sq.m Site Bhandup Stn How to access site from Bhandup Stn.

17. Purpose of the Retaining walls at site and where are they located: The Project is a Residential building having stacked parking with commercial shops on the ground floor besides the road. The main purpose of basement was that the client wanted to have stacked parking in the basement till 4 th floor above the ground floor. Cantilever Retaining wall has been used with overall depth of 3.5 meters. The shear walls, the columns and retaining walls were chemically treated for waterproofing. The position of the retaining walls is indicated with the red outline in the structural plan of the building. Section AA’of Stack Parking . A’ A The site is small is scale so the idea of stack parking was undertook by builder. The Retaining walls are used to have a small basement underneath as well as they carry loads of the stack parking above. Structural Plan of Project

18. Where else are the Retaining walls used on site: Retaining walls are used for the underground water tanks also for the suction and fire fighting tanks. The position of the tanks is underground and they are accessible by the Manholes above also the retaining walls are treated well with chemicals for water proofing purpose Plan showing positions of retaining walls for the water tanks Typical section of the RCC underground water tank

19. Images of the Retaining walls on site: View A , the retaining walls for the stack parking purpose above them. View B , the retaining walls for the underground water tanks. View C , the Plinth beams at the Front open space A C B Plan of the project. The pic besides shows the ‘q’ junction detail which is applied in between the intersection of two retaining walls.

20. Thank you!..... Group Members: Rohan Narvekar Abhijit Nayak Nishant Gupta Vishakha Sawatkar Shital Dongre