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1. RETAINING
WALLS

2. Retaining walls are structures constructed for the purpose of
retaining earth or other materials like coal, ore, water etc.
• It may also be defined as a wall provided to maintain ground at two
different levels. Provisions of retaining walls become necessary in the
construction of hill roads, embankments, bridge abutment, basement in
buildings, water reservoir, in preventive measures against soil erosion, in
landscaping etc.
• The material retained by the wall is generally known as backfill. The backfill
may be horizontal i.e., levelled with the top of wall or it may be inclined at
certain angle to the top.
• The inclined fill is also known as surcharge. Besides loads due to retained
material, the retaining wall may also be subjected to surcharged load (due
to automobile, rail road etc.) acting directly on the wall as well as on the
backfill.
• The retaining wall should be stable enough to resist all type of forces acting
on it.

4. Retaining walls have primary function of retaining soils at an angle
in excess of the soil’s nature angle of repose.
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:
1. Overturning of the wall does not occur
2. Forward sliding does not occur
3. Materials used are suitable
4. The subsoil is not overloaded

5. • Back fill: The soil placed behind a wall.
• Back fill slope: Often the back fill slopes upward from the back face of the wall. The
slope is usually expressed as a ratio of horizontal to vertical (e.g. 2:1).
• Footing (or foundation): That part of the structure below the stem that supports and
transmits vertical and horizontal forces into the soil below.
• Grade: The surface of the soil or paving; can refer to either side of the wall.

6. • Heel: That portion of the footing extending
behind the wall (under the retained soil).
• Retained height: The height of the earth to be
retained, generally measured upward from the
top of the footing.
• Stem: The vertical wall above the foundation.
• Surcharge: Any load placed in or on top of the
soil, either in front or behind the wall.
• Toe: That portion of footing which extends in
front of the front face of the stem (away from
the retained earth).
• Weep holes: Holes provided at the base of the
stem for drainage. Weep holes usually have
gravel or crushed rock behind the openings to
act as a sieve and prevent clogging. Poor
drainage of weep holes is the result of weep
holes becoming clogged with weeds, thereby
increasing the lateral pressure against the wall

7. Factors which designer need to take account:
• Nature and characteristics of the subsoil's
• Height of water table – the presence of water can create
hydrostatic pressure, affect bearing capacity of the subsoil
together with its shear strength, reduce the frictional
resistance between the underside of the foundation
• Type of wall
• Materials to be used in the construction

9. Types of walls:
• Mass retaining walls
• Cantilever walls
• Counterfort retaining walls
• Precast concrete retaining walls
• Precast concrete crib-retaining walls

10. Mass retaining walls:
• Sometimes called gravity walls and rely upon their own mass
together with the friction on the underside of the base to
overcome the tendency to slide or overturn
• Generally only economic up to 1.8 m
• Mass walls can be constructed of semi-engineering quality bricks
bedded in a 1:3 cement mortar or of mass concrete
• Natural stone is suitable for small walls up to 1m high but
generally it is used as a facing material for walls over 1 m
• The wall is so proportioned that the dead weight of the wall
provides required stability against the thrust exerted by the
backfill including surcharge.

11. BRICK MASS RETAINING WALL

13. MASS CONCRETE RETAINING WALL WITH STONE FACINGS

15. Cantilever Walls:
• Usually of reinforced concrete and work on the principle of
leverage where the stem is designed as a cantilever fixed at the
base and the base is designed as a cantilever fixed at the stem
• Economic height range of 1.2 m to 6 m using pre-stressing
techniques
• Any durable facing material can be applied to the surface to
improve appearance of the wall.

16. TWO BASIC FORMS:
• A base with a large heel
• A cantilever with a large toe
CANTILEVER T CANTILEVER L

20. Counterfort Retaining Walls:
• Can be constructed of reinforced or Prestressed concrete
• Suitable for over 4.5 m
• In this type of wall the base slab as well as the stem of the wall
span horizontally as continuous slabs between vertical brackets
known as counterforts.
• The counterforts are provided behind the wall (on the backfill
side) and are subjected to tensile forces. The spacing of the
counterforts may vary from of the height of wall. The more the
height of the wall, the closer should be the spacing of
counterforts

24. Precast concrete retaining wall:
• Manufactured from high-grade pre cast concrete on the
cantilever principle.
• Can be erected on a foundation as permanent retaining
wall or be free standing to act as dividing wall between
heaped materials which it can increase three times the
storage volume for any given area
• Other advantages- reduction in time by eliminating
curing period, cost of formwork, time to erect and
dismantle the temporary forms
• Lifting holes are provided which can be utilized for fixing
if required

26. Pre cast concrete crib-retaining walls:
• Designed on the principle of mass retaining walls
• A system of pre cast concrete or treated timber components
comprising headers and stretchers which interlock to form a 3
dimensional framework or crib of pre cast concrete timber units
within which soil is retained
• Constructed with a face batter between 1:6 and 1:8
• Subsoil drainage is not required since the open face provides
adequate drainage.