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