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REINFORCED EARTH
STRUCTURES
P . Suresh B .Tech.,
The soils which have little tensile strength can be strengthened by the inclusion of materials with high tensile strength . The principle is same as adopted in reinforced concrete.
This mobilization of tensile strength is obtained by surface interaction between the soil and the reinforcement elements through friction and adhesion.
The reinforced earth technique is useful in urban locations where availability of land is minimum and construction is required with min disturbance to traffic.
If the soil is cohesion less like sand the resistance will be friction and if the soil is cohesive the bond stress will be adhesive.
BASIC CONCEPT OF REINFORCED EARTH
It is very important to note that the total horizontal earth pressure is resisted by the frictional force between the soil and reinforcing element and the design will be made with required no. of layers vertically at adequate spacing
Hence there will not be any horizontal thrust on facia panels/blocks and these elements are non structural and are provided only to prevent erosion, loss of material at the face of re wall. The foundation provided for facia panels is only to take the self weight of panels, kerb over wall etc., but not for resisting the horizontal thrust.
The facia wall facilitates to keep the reinforcing elements at desired level and to retain fill material.
Compaction of fill material is not compulsory for walls without any vertical loads like gardens etc. For roads the compaction of fill shall be done as usual. But care must be taken that the compaction equipment like rollers etc should go not closer than 2m to wall facing
Generally the size of square panels shall be 1500 x 1500mm. The thickness of panels shall be 180 mm and concrete grade of M35 shall be adopted. Nominal reinforcement consisting of 8mm Hysd bars shall be provided both ways at center
A leveling pad with m15 grade concrete shall be casted to provide a firm, level, and flat surface on which the facing units can be erected to the correct line, level. The width of footing is generally 600mm, and depth of 200mm. The leveling pad shall be cured for 24 hours prior to commencement of placing of panels.
No plant or equipment with a weight of more than 1500 kg shall be allowed to operate within a distance of 1.50m from the facing
A light weight less than 1500kg vibratory roller or vibratory plate compactor may be used in this zone
Beyond a distance of 1.50m from the facing a static or vibratory roller of 8- 10 t may be used for compaction.
CONCEPT OF REINFORCED EARTH
SKETCH SHOWING ACTIVE AND RESISTANT ZONES
STABLE SLOPE STEEP SLOPE
EMBANKMENT
EXISTING G.L.
SOIL FORMATION
COMPONENTS OF REINFORCED EARTH STRUCTURE
1) REINFORCING ELEMENT
2) SOIL BACK FILL
3) FACING ELEMENT
TYPES OF REINFORCING ELEMENTS
Strips with metals like steel, aluminum, copper, polymers, glass fibre reinforced plastic etc.
Grids with steel, galvanized weld mesh, polymers (geo grids)
Sheet reinforcement with steel, fabric (geotextile)
Planks with timber, reinforced concrete, pre stressed concrete.
SKETCH SHOWING COMPONENTS OF RE WALL
The fill material for reinforced earth structures shall be
preferably cohesion less and it should have angle of
interface friction between the compacted fill and
reinforcing element not less than 30.
REQUIREMENT OF SELECTED FILL
Plasticity index should be less than 6
The size of fill material should not exceed 125 mm
The soil should be coarse grained, and not more than
10% of particles shall pass 75 micron sieve
The earth reinforcement coefficient of friction should
be higher than 0.40
COEFFICIENT OF INTERACTION BETWEEN SOIL AND GEO GRID
S.NO TYPE OF SOIL COEFFICIENT Ǿ VALUE
1) CRUSHED ROCK,GRAVEL 0.90 TO 1.0 40 TO 50
2) SANDS 0.85 TO 0.95 28 TO 40
3) PULVERISED FUEL ASH 0.80 TO 0.85 --
4) CLAY 0.60 TO 0.70 < 12
COMPONENTS OF RE WALS
SKETCH SHOWING RE WALL DETAILS, DRAINAGE LAYER
SKETCH SHOWING RE WALL SYSTEM
MINIMUM LENGTH OF REINFORCEMENT
TYPE OF STRUCTURE MIN. REINFORCEMENT LENGTH
1)RETAINING WALLS 0.70 H (OR) MIN 3.0M
2)BRIDGE ABUTMENTS (0.60H+2) OR MIN 7.0 M
SECTION SHOWING RE WALLS REINFORCEMENT
SKETCH SHOWING WRAP AROUND GEOTEXTILE RE WALLS
SKETCH SHOWING DIFFERENT TYPES OF RE WALLS
TYPES OF FACING ELEMENTS
1)REINFORCED CONCRETE PRECAST
PANELS
2)PRECAST HOLLOW BLOCKS OR SOLID
BLOCKS
3) MILD STEEL SHEET
4) RUBBLE FACIA WITH WIRE MESH
TYPICAL SKETCH SHOWING ONE TYPE OF FACIA PANELS
SKETCH SHOWING TIE IN FACIA WALLS
SKETCH SHOWING REINFORCEMENT CONNECTION WITH TIE
PHOTO SHOWING CONNECTION OF REINFORCEMENT WITH TIE
P.C.C. BED UNDER REINFORCED EARTH WALL
INSIDE (EARTH FACE ) FACE OF RE WALL WITH FIRST ROW OF FACIA PANELS.
PHOTO SHOWING FOUNDATION OF FACIA PANELS
SKETCH SHOWING PLACEMENT OF FIRST ROW OF PANELS
PHOTO SHOWING SCAFFOLDING FOR FIRST LAYER OF PANELS
RAISING OF FACIA WALL WITH PRECAST PANELS
SKETCH SHOWING JOINTING OF PANELS
THE PANELS MAY BE GIVEN SLIGHT TILT TOWARDS SELECTED FILL TO ALLOW OUTWARD MOVEMENT SO
THAT IT WILL BE TRULY VERTICAL AFTER LOADING
PHOTO SHOWING FURTHER LAYERS OF R.C.C. FACIA PANELS
SKETCH SHOWING PLACEMENT OF R.C.C. FACIA PANELS
SKETCH SHOWING IN SIDE OF FACIA PANELS DURING ERECTION
PHOTO SHOWING CENTERING FOR CHECKING SPACING ,PLUMB
STEEL REINFORCEMENT WITH STONE DUST FILL WITH R.C.C. FACIA PANELS
STEEL FACIA PANELS WITH STEEL STRIPS AND FILL
STEEL REINFORCEMENT WITH STEEL FACIA AND GRAVEL FILL
CLOSE UP VIEW OF STEEL STRIP REINFORCEMENT ,FACIA PANELS
RE WALL WITH CRUSHED AGGREGATE FILL, FACIA PANMELS
RE WALL WITH STEEL REINFORCEMENT
PHOTO SHOWING STEEL REINFORCEMENT IN SOIL ,FACIA PANEL
STEEL REINFORCEMENT WITH R.C.C. FACIA PANELS
CLOSEUP VIEW OF STEEL REINFORCEMENT
PHOTO SHOWING GEOGRID REINFORCEMENT WITH HOLLOW BLOCKS FACIA
PHOTO SHOWING GEO SYNTHETIC REINFORCEMENT ,FACIA BLOCKS
PHOTO SHOWING GEO GRID REINFORCEMENT, OVER LAP
CLOSE UP VIEW OF GEO TEXTILE REINFORCEMENT
GEO GRID REINFORCEMENT WITH PRECAST C.C.BLOCKS FACIA
CLOSE UP VIEW OF GEOGRID REINFORCEMENT
GEOGRID REINFORCEMENT WITH HOLLOW BLOCKS FACIA
METAL REINFORCEMENT, STONE DUST FILL, HOLLOW BLOCKS FACIA
DRAINAGE LAYER, SELECTED FILL, C.C. HOLLOW BLOCKS FACIA
SPREADING OF GEO GRID
SPREADING OF GEO GRID WITH FACIA BLOCKS
SPREADING OF FILL MATERIAL (CRUSHED ROCK), GEOGRID
STONE DUST FILL, R.C.C. FACIA PANELS
PHOTO SHOWING COMPACTION OF FILL MATERIAL
PHOTO SHOWING COMPACTION WITH PLATE COMPACTOR CLOSE TO FACIA WALLS
PRECAST BLOCKS FACIA WITH STEEL REINFORCEMENT
METAL REINFORCEMENT WITH PRECAST HOLLOW BLOCKS FACIA
SPREADING OF SELECTED FILL STONE DUST
GEOTEXTILE FIXED WITH FACIA WALLS AND ERECTION OF FACIA PANELS
ERECTION OF FULL HIGHT FACIA WALLS
ERECTION OF PRE-CAST FACIA PANELS
ERECTION OF PRECAST FACIA PANELS WITH TIES
ERECTION OF FULL HIGHT FACIA PANELS
ERECTION OF FULL HIGHT FACIA PANEL
COMPLETED RE WALL WITH FACIA PANELS
PHOTO SHOWING TIMBER GRID RETAINING WALL
COMPLETED BRIDGE ABUTMENT AS RE WALL
COMPLETED BRIDGE ABUTMENT AS RE WALL WITH FULL HIGHT CONCRETE FACIA PANELS
THANK YOU
P. SURESH. Deputy Executive Engineer
(R&B) sub division, Udayagiri.
CELL NO: 9440818349