Retaining walls and Breast walls

Content of The Article :

Retaining walls and Breast walls, Retaining walls,Retaining wall Terminology,Back fill,Back fill slope,Batter,Dowels,Footing, Footing key,Weep wholes, Grade, Heel, Horizontal temperature/shrinkage reinforcing, Keyway, Principal reinforcing, Retained height, Stem, Surcharge, Toe, Breast Walls.

Retaining walls.

The walls constructed for retaining or supporting earth against their back are called retaining walls. Earth cannot remain vertical but would be in a state of equilibrium when it assumes a natural angle which is called angle of repose. If it is desired to be retain the earth vertically, that portion of the earth will have to be supported by a wall called retaining wall. The back of the wall is in the form of steps and the face of the retaining wall may be either vertical or battered. The width at the base will depend upon the height of earth to be retained as the more the height, the greater will be the pressure at the base and the top can be kept 2 bricks thick .

Retaining wall Terminology

Backfill:

The soil placed behind a wall.

Backfill slope:

Often the backfill 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).

Batter:

The slope of the face of the stem from a vertical plane, usually on the inside (earth) face.

Dowels:

Reinforcing steel placed in the footing and bent up into the stem a distance at least equal

to the required development length.

Footing (or foundation):

That part of the structure below the stem that supports and transmits vertical and horizontal forces into the soil below.

Footing key:

A deepened portion of the footing to provide greater sliding resistance.

Grade:

The surface of the soil or paving; can refer to either side of the wall.

Heel:

That portion of the footing extending behind the wall (under the retained soil).

Horizontal temperature/shrinkage reinforcing:

Longitudinal horizontal reinforcing usually placed in both faces of the stem and used primarily to control cracking from shrinkage or temperature changes.

Keyway:

A horizontal slot located at the base of the stem and cast into the footing for greatershear resistance.

Principal reinforcing:

Reinforcing used to resist bending in the stem.

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. Unless properly designed and maintained, weep holes seldom “weep”.

Alternatively, perforated pipe surrounded with gravel and encased within a geotextile can be used

to provide drainage of the back fill.

Breast Walls.

A breast wall is constructed to protect the natural sloping ground from the cutting action of natural agents. Breast walls also prevent slides of unreliable soils. The breast walls may be 0’6 m wide at the top. Weep holes should be provided at regular interval among the length of the wall to relieve the walls of saturated earth pressure. The breast wells are so designed that their line of pressure should be normal to the earth pressure or thrust. (See Fig. 2.50)

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