RETAINING WALLSA.B.C.M.

Sneha CoutinhoT. Y. B.Arch – ARoll No. 7Bharati Vidyapeeth C.O.A.

INTRODUCTION• A 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.

• To retain soil at a slope which is greater than it would naturally assume, usually at a vertical or near vertical position.

• The material retained or supported by a retaining wall is called backfill.• Backfill may have its top surface horizontal or inclined.• The position of the backfill lying above the horizontal plane at the

elevation of top of wall is called surcharge & its inclination to the horizontal is called as Surcharge angle.

• Retaining walls have primary function of retaining soils at an angle in excess of the soil’s nature angle of repose.

PARTS OF A RETAINING WALL

DESIGN• Walls within the design

height range are designed to provide the necessary resistance by either their own mass or by the principles of leverage.

Design consideration:• Overturning of the wall

does not occur• Forward sliding does not

occur• Materials used are suitable• The subsoil is not

overloaded

DIAPHRAGM WALL• Diaphragm wall is a continuous

wall constructed in the ground to facilitate certain construction activities, such as: - a retaining wall - a cut-off provision to support deep excavation - the final wall for basement or other underground structure (e.g. tunnel and shaft) - a separating structure

between major underground facilities - a form of foundation (barrette pile – rectangular pile)

RETAINING WALLS

GRAVITY RETAINING

WALLSSEMI GRAVITY

RETAINING WALLS

CANTILEVERED RETAINING

WALLS

COUNTERFORT RETAINING

WALLS

GRAVITY WALLS• The “gravity wall” resists the

earths pressure exerted by backfill by its own self weight (dead load) .

• It is usually built in stone masonry, and occasionally in plain concrete.

• provides stability by virtue of its own weight , and therefore, is rather massive in size

• Plain concrete gravity walls are not used for heights exceeding about 3m, for economic reasons

• Stress developed is very low.• These walls are so proportioned that no tension is developed

anywhere and the resultant of forces remain within the middle third of the base

SEMI GRAVITY RETAINING WALLS• Semi-gravity walls

resist external forces by the combined action of self weight, weight of soil above footing and the flexural resistance of the wall components.

CANTILEVERED RETAINING WALLS

• The “Cantilever wall ” is the most common type of retaining structure and is generally economical for heights up to about 8m.

• The structure consists of vertical stem , and a base slab, made up of two distinct regions, viz., a heel slab and a toe slab.

• “Stem” acts as a vertical cantilever under the lateral earth pressure

• “Heel slab” acts as a horizontal cantilever under the action of weight of the retained earth (minus soil pressure acting upwards from below)

• “Toe slab ” acts as a cantilever under the action of resulting soil pressure acting upward.

T-CANTILEVER

L-CANTILEVER

COUNTERFORT RETAINING WALLS• For large heights, in a

cantilever retaining wall, the bending moments developed in the stem, heel slab and toe slab become very large and require large thickness.

• The bending moments can be considerably reduced by introducing transverse supports, called counter-forts.

• Counterfort wall are placed at regular intervals of about1/3 to ½ of the wall height, interconnecting the stem with the heel slab

• The counterforts are concealed within the retained earth on the rear side of the wall.

• Can be constructed of reinforced or pre-stressed concrete• Suitable for over 7m

• The counterforts subdivide the vertical slab (stem) into rectangular panels and support them on two sides(suspender-style), and themselves behave essentially as vertical cantilever beams of T-section and varying depth.

SECTION SHOWING R.W FOR BASEMENT

ALTERNATIVES TO RETAINING WALLS

CELLULAR CONFINEMENT• Cellular confinement systems

have become increasingly popular for earth retention applications.

• They can be constructed as a gravity wall or a "geogrid" wall which consists of vertical layers of geocells with geogrid reinforcement installed behind the face of the wall every few layers of the geocell depending on design.

• Cellular confinement systems (geocells) are also used for steep earth stabilization in gravity and reinforced retaining walls with geogrids.

• Geocell retaining walls are structurally stable under self- weight and externally imposed loads, while the flexibility of the structure offers very high seismic resistance.

• The outer fascia cells of the wall can be planted with vegetation to create a green wall.

• Soil nailing is a technique in which soil slopes, excavations or retaining walls are reinforced by the insertion of relatively slender elements - normally steel reinforcing bars.

• The bars are usually installed into a pre-drilled hole and then grouted into place or drilled and grouted simultaneously.

• They are usually installed un-tensioned at a slight downward inclination.

• A rigid or flexible facing (often sprayed concrete) or isolated soil nail heads may be used at the surface.

GABION MESHES• This type of soil

strengthening, often also used without an outside wall, consists of wire mesh "boxes, which are filled with roughly cut stone or other material.

• The mesh cages reduce some internal movement and forces, and also reduce erosive forces.

• Gabion walls are free-draining retaining structures and as such are often built in locations where ground water is present.

BUTTRESS WALL• It is similar to counterfort wall,

except that the transverse stem supports, Called buttress, are located in the front side, interconnecting the stem with the toe slab(and not with heel slab, as with counterforts)

• Although the buttresses are structurally more efficient (and more economical) counterforts, the counterfort wall is generally preferred to the buttress wall as it provides free usable space (and better aesthetics)in front of the wall.