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Reinforced soil earth Wall (RE/RS wall) uses and its specifications

 This article includes :-

1- What is Reinforced soil earth Wall (RE/RS wall)?
2- why and where is used Reinforced soil earth Wall(RS/RE wall) ? 
3- What are the types of RS/RE wall?
4 - Material used in RS/RE Wall. 
5 - What is the Construction procedure of RS/RE Wall? 
6 - What are the tolerance limits for various items(like panels,joints, levelling pad top etc.) of RS/RE Wall? 
7 - Measurement Of RS/RE Wall.

1- What is RS/RE wall (Reinforced soil earth wall) ?


RS/RE Wall (Reinforced soil earth wall) is a self stabilized and rigid structure that is designed or used to restrain the soil deformation and achieve the desired soil slope.
The stability of RS/RE wall is maintained by its own weight.
The friction between reinforcement (metallic elements or polymeric elements) and soil keeps the structure in its position. Due to this friction force ,less lateral force exerts on precast panel members of RS/RE wall. 



2- why and where is used Reinforced soil earth Wall? 


RE/RS Wall (Reinforced soil earth wall) is constructed because it resist the lateral pressure of soil. RE wall also prevents soil from erosion and collapsing or slipping.


RE Walls (Reinforced soil earth wall) are used where soil has to be bounded at two different elevations.RE wall is also constructed in road construction locations where proper space is not available to maintain the soil slope.


3- What are the types of RS/RE wall? 
It was seen that any of below three types RS/RE wall is used.
(I) Reinforced soil earth wall with modular facia
(II) Reinforced soil earth wall with Gabion facia with integrated tail
(III) Reinforced soil earth wall with concrete panel facia.


4 - Material used in RS/RE Wall. 


A- Wooden wedge


Wooden Wedge are used in construction of reinforced soil earth wall to maintain batter (a receding upward slope of the outer face of a wall or other structure) of panels. These are also used to match the facial of panels. 

As per practical consideration, 4 to 6 numbers of wooden wedge are required per vertical joint for the length of structure during construction.






B- Shoulder clamp or H type clamp


Shoulder clamps are used to hold the panels in required position during erection of RE/RS wall. 


C- EPDM Rubber Pad


The full form of EPDM is Ethylene Propylene Diene Monomer. EPDM rubber pad has very good properties in cold and hot region i.e weather, ozone & water resistance at wide range of service temperature (-50°C to 140°C) with good resilience proprties at low and high temperature, excellent heat ageing properties and acid resistance properties.


Some basic properties of EPDM rubber pads are being given below. 


General Shape: Rectangular
Thickness: 20mm, 22mm
Size: 150 x 70 x 22mm
Color: Black
Hardness: 80 +/- 5 Shore A
Density: 1.19 +/- 0.03 g/cm3
Tensile Strength: Min 12 MPa
Elongation at Break: Min 200%
Change in Tensile Strength: 25%
Change in Elongation: 25%
Tear Strength: 38 daN/cm
Ash Content: Max 5%


EPDM rubber pads are used between RE panels to provide better stability and bonding. 






D- reinforcement


There are various types of reinforcements which are used in reinforced soil earth walls .
1 - Metallic elements like bars, strips, plates etc. ( Metallic reinforcement in form of mesh)
2 - Polymeric elements like strips, grids, rods, mesh etc. 

Reinforcement used to resist lateral loads can be metallic or polymeric. Metallic reinforcement should be inextensible and polymeric reinforcement should be extensible. Strength of polymeric reinforcement is largely affected by temperature and time (creep) because Polymers are visco-elastic materials.


Tensile strength of reinforcement is evaluated by conducting a wide width tensile test ( as per ISO 10319 or ASTM D 6637or EN 10223-3 for woven steel wire mesh).


All types of Reinforcements are taken beyond the Rankine zone into the resistant zone to ensure sufficient bond and anchorage.


Creep should be estimated keeping in mind the ambient temperature which in many parts of the country exceeds 40°C during summer, though in-situ temperatures may not exceed 30° - 35°C. The designer shall provide partial safety factors for creep, for 20°, 30° and 40°C degrees. These results should also include creep rupture and creep strain at these temperatures.


Partial Safety factor used in design should correspond to the temperature calculated by the procedure given in EN/ISO 20432. The design temperature should be taken as half way between the average yearly air temperature and normal daily temperature (shade temperature) for the hottest month at the site. The shade air temperature in a zone cab be obtained from IRC-6.


Polymeric reinforcement shall have minimum of 10000 hours creep test data or SIM test data at different temperatures to evaluate partial material factor for creep. Manufacturing of reinforcement should confirm to ISO 9001 standard.


Metallic reinforcement exhibits relatively negligible creep. 









* Lifting equipment(Shikanja) is used to lift and fix the panels at required locations 




E - Geo composite 
Geocomposite is a combination of geotextile and geogrid; or geogrid and gromembrane; or geotextile, geogrid, and geomembrane; or any one of these three materials with another material (e.g. deformed plastic sheets, steel cables, or steel anchors). 














F - Geotextile
Non woven Geotextiles are permeable so allow water to pass through.
When non woven geotextile is used in association with soil, it has the ability to filter /separate soil stabilization. 
The Minimum width of geotextile strip to cover gaps between panels is 100 mm. 






5 - What is the Construction procedure of RS/RE Wall? 


The responsibility of the construction of a RS/RE Wall will completely depends on the main contractor. 


Construction steps of RE/RS are being described below -
A- To achieve design parameters Foundation treatments are done if required.B- Layout of RS/RE wall structure is done on ground as per drawing.
C - Excavation of soil is done and the soil is compacted up-to required dimensions with 95% (Dry density) compaction of Modified Proctor Density.
D - An initial levelling pad of 150 mm thick using M15 (Min. concrete grade) plain cement concrete having required width to be placed below the first row of fascia layer.








E - The first layer of blocks/panels is fixed on the levelling pad with proper offset as per drawing. 
F - Make proper alignment of panels/blocks (The alignment of the block/panels/facing element must be checked regularly to make sure,the wall is straight or curve as per drawing)
G - Drainage material(as per required thickness) shall be placed at the back facing block/panel and in the hollows of facing block. The drainage material shall be compacted with vibratory plate compactor and within the block cavities. No heavy compaction equipment should be allowed to operate within 1.5 m of the back of face panel.
H - Placing the reinforced soil backfill behind the drainage zone and compacting to a minimum of 95 percent Modified Proctor density/80 percent Relative Density. 
The backfill should be placed and compacted in layers(The compacted thickness of each layer shall not exceed 200 mm.).
At no stage of construction the compaction or any other equipment shall be allowed to operate directly on the reinforcement.
I -When in direct contact, the backfill material and the drainage material shall be separated using permeable non-woven geotextile.
J - The successive face element shall be placed as per required line and level. In several cases outward movement has been observed due to poor connection of reinforcement with face element. The same procedure shall be repeated until the final layer of reinforcement is reached.
K - Before placing the drainage material and backfill, the reinforcement should be cut up to required length and placed on top of the face block. 
The reinforcement should be stretched to ensure that there are no wrinkles and the reinforcement is taut.
L - proper care should be taken that geogrid is slightly away from the external junction of outside face of fascia block. 
This will ensure that the geogrid does not protrude out of the wall and is prevented from UV ray exposure.
M - Second layer of facia block is laid over the geogrid, so that geogrid is completely interlocked between the blocks. The above procedure is repeated for subsequent geogrid layers. 
N - Where panels are used, the reinforcement should be connected to connector embedded in the panel.
O - When panels are used it is desirable to keep an initial inward better ( A receding upward Slope of the outer face of a wall) as given in the drawing.
P - Where the retained fill is borrowed and is different from the reinforced fill the construction should progress simultaneously. It is desirable that face of the blocks be profiled to have an inward batter of 2-4 degrees. 


6 - What are the tolerance limits for various items(like panels,joints, levelling pad top etc.) of RS/RE Wall? 


The construction tolerances shall be as per the following -


(A) Casting of pre-cast RCC panels: All elements shall be manufactured within the following tolerances: 



All dimensions within ± 5 mm 
Evenness of the front face: ± 5 mm over 1500 mm 
Difference between lengths of two diagonals: 5 mm maximum 
Thickness: + 5 mm (-) 0 mm 

(B) Tolerances for Faces of Retaining Walls 




(C) Dimensional Tolerances for Modular Blocks


Dimensions of modular concrete blocks shall not differ more than ± 2.5 mm for length and width and ± 1.5 mm in height.


(D) Minimum Vertical Movement Capacities of Facing Systems 






Crash Barrier : Horizontal impact load of 29 kN/m shall be considered in the design of crash barrier, which load shall be resisted by the upper two layers of the reinforcement over the full length. 


Where the height of reinforced soil wall exceeds 10 m, the designer may consider providing a berm. The minimum width of such berm shall be 1.5 m. 


7 - Measurement Of RS/RE Wall. 


(a) Reinforced Soil Wall 
Tie measurement for payment for reinforced soil wall shall be in square metres of finished work of each face and shall be measured in the plane of final inclination specified in the drawings. The measurement of length shall be the finished work along the length of the road. The measurement of height along the slope shall be done from the top level of the footing on witch the facia element is placed to the top of the capping beam. 


Measurement for friction slab and crash barrier shall be in linear metres (Running metres) and separately.




(b) Reinforced Soil Slope 


The measurement for payment for reinforced soil slope shall be in square metres of finished work of each face and shall be measured in the plane of final inclination specified in the drawings. The measurement of length shall be the finished work along the length of the road. The measurement of height along the slope shall be done from the top of the leveling pad, where provided, to the top of the embankment. Where leveling pad is not provided, the height shall be measured, in the final plane of inclination specified in the drawings, from the bottom of the slope face. 


(c) RATES 


The rate shall include cost of material, labour, plant, royalties, handling, storage and transportation expenses, cost of bed block, leveling pad, facia elements, capping beam, connectors, reinforcing elements, scaffolding, supply of the specified filter media material, supply of soil fill for the reinforced as well as unreinforced zone of the quality specified in the contract, placing, spreading and compaction through mechanical means. 


The rate shall include full compensation for design, drawings and testing of materials. 
The rate shall include the cost of investigations, design and construction of ground improvement measures. 


Most important points about Reinforced soil earth wall (RS/RE Wall)


• Minimum thickness of RS/RE wall panels is 180 mm. (including facia textures, logos and embellishments)
•Minimum Concrete grade of RS/RE panels is M 35.
• Minimum width of geotextile strip to cover gaps between panels is 100 mm. 
•Height of point of impact at crash barriers above top of pavement is 800 mm. 
•Maximum spacing of reinforcing elements shall not exceed 800 mm for RS/RE wall using panels and blocks. 
•Minimum thickness of strip footing ( levelling pad PCC) is 150 mm. 
•Minimum width of strip footing ( levelling pad PCC) is 350 mm. 
•Minimum concrete grade for levelling pad PCC( strip footing) is M 15.
•Minimum depth of embedment below finished ground level at the foot of wall is 1000 mm. 
•Maximum compacted soil thickness of each layer is 200 mm. 

•Various types of reinforcements used in RS/RE wall
1 - Metallic elements like bars, strips, plates etc. 
2 - Metallic reinforcement in form of mesh
3 - Polymeric elements like strips, grids, rods mesh etc. 
Minimum length of reinforcement shall be 0.7 H to 3 met. Whichever is greater.
Where H is design height (depth of embedment plus height above ground level) of the RS/RE wall. 


Thank you 
Mukesh Kumar 

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