As its name suggests, a retaining wall retains earth laterally when there is a drastic change in elevation, preventing it from spilling onto the lower level. Retaining walls can range from simple raised garden beds to large walls several metres in height, built to control erosion, redirect water, and prevent landslips.
A retaining wall is normally needed when a slope has lost its natural integrity or is composed of inherently unstable materials such as gravel or sand. Most retaining walls fall into one of three categories:
- Gravity retaining walls – these rely on their own sheer weight to anchor them in place and prevent the earth from slipping. They are normally thick and heavy and made from materials such as stone, concrete and brick, and they are often tilted back slightly towards the soil they are supporting to compensate for the pressure.
- Pile retaining walls – these rely on piles or sheeting driven into the ground which counteract the weight of the slope above from below the surface of the ground, much in the way a lever works.Taller walls of this type often need to be supported with a tie-back cable planted in the soil behind the wall to help keep it vertical.
- Cantilevered retaining walls – these rely on steel–reinforced concrete structures cut into the slope. The weight of the slope presses down on their footings to counteract the downhill flow of earth.This extra support at their base means these walls can be made much thinner than gravity walls.
METHOD OF STATEMENT
- APPLICATION OF ELASTOPLASTOMERIC MEMBRANE ON RETAINING WALLS
The purpose of the application of waterproofing material is to prevent water from percolating or penetrating into any underground concrete members. When water penetrates into the sub-grade concrete like foundation, such as : mat foundation, footing, tie beam etc. the steel reinforcement that embedded in the concrete would corrode due to chemical reaction caused by water, thereby, resulting to collapsing of structure in most cases.
In this method of statement, we shall be using the membrane type of waterproofing ; this type of water proofing is advisable for big structures that have deeper foundation, where water pressure is extremely high.
Here is the method of statement for application of waterproofing membrane.
PURPOSE AND SCOPE
The purpose of this method of statement is to describe the measures and ways of proper application of waterproofing membrane/Felt in our project. Work shall be carried out as project specification.
- Work preparation and application of primer:
- Any undulations or protrusions on the surface would be removed in order to obtain smooth surface. The surface must be thoroughly cleaned and freed from dust, dirt loose materials, oil or grease.
- 50x50mm size fillet made of cement-sand (1:3) mix would be placed along corners of walls or neck columns and any other junctions.
- For horizontal waterproofing membrane application: Elastoplastomeric membrane/Felt shall be laid fully torched on blinding concrete with minimum of 100m end laps and 150mm side laps.
- The blinding surface shall be primed with the primer recommended by the manufacturer of the membrane prior to placing the membrane.
- Waterproofing membrane installation shall be performed using cylinder fed propane gas torch, trowel to seal the seams of the membrane and knife for cutting.
- The membrane is then placed in the correct torching on position then re-rolled for about half of its length without changing its orientation.
- The membrane is then un-rolled again and torched on pressing the melted area against the substrate.
- Repeat till the entire length of the membrane is bonded firmly onto the surface.
- An extra length of minimum 300mm of the horizontal membrane shall be left to carry up the vertical surface to maintain continuity of the membrane and be protected as above.
- For vertical application of 3mm thick Elastoplastomeric membrane/felt shall be applied to all vertical surfaces of gunited shoring or blockworks wall.
- Before applying the waterproofing membrane, concrete surfaces shall be primed with primer as recommended.
- The extra portion of 300 mm of the horizontal membrane left shall be turned up and wrapped on to the vertical primed surfaces. The continuity of the membrane shall be maintained by minimum laps of 150mm.
- The membrane on the exposed external vertical surfaces shall be carried up to a minimum of 150 mm above the finished ground level (i.e. side walk, parapet, etc.) and tucked into a continuous groove provided for the same and secured firmly.
- The membrane fixed on the gunited or concrete wall shall be protected from any damage due to rebar fixing, formworks, concreting of raft, retaining wall works with protection board/plaster fixed to the membrane.
- All areas of the membrane exposed above ground shall be protected with appropriate flashing.
- Fix protection board/plaster on vertical surface before backfilling.
DURABILITY 1O – 15 years