CHAPTER ONE
RETAINING WALLS
Retaining walls are structures used in providing stability for earth or materials where conditions do not give room for the material to assume its natural slope and are mostly used to hold back soil banks, coal or over, piles and water.
Retaining walls are distinguished from aone another based on the method of achieving stability.
There are six type of retaining walls and are:
i.                    The gravity wall
ii.                  The cantilever wall
iii.                The counterfort retaining wall
iv.                Buttressed retaining wall
v.                  The crib walls
vi.                Semi-gravity wall
Bridge abutments are often retaining walls with using wall extension to retain the approach fill and provide protection against erosion. They differ in two major respect from the usual retaining walls.
i.                    They carry and reactions from the bridge span.
ii.                  They are restrained at the top so that on active earth pressure is unlikely to develop.
Foundation walls of building mduding residential construction and retaining walls, whose function is to contain the earth of the basement.
Retaining walls are required to be of adequate proportion to resist over turning and sliding as wall as being structurally  a proportion to resist over turning and sliding as wall as being structurally adequate.
Terms used in retaining wall design are shown below (f.g 1-2).The toe is both the front base perfection and forward edge, similarly for the heel the backward perfection.
 
Fig(1-1)
The different types representation diagrams of retaining walls are shown in fig (1-2) below.
                                
a) Gravity walls of stone masony, brick, or plain concrete
                                      
Bridge abutement
      
The retaining wall as a whole must satisfy two basic conditions. They are
i.                    The base pressure as the toe of the wall must not exceed the allowable bearing capacity of the soil.
ii.                   The factor of safety against sliding between the are and the underlying soil must be adequate a value of at least usually  being specified. (Rit Craig 2nd edition soil mechanical published by van nostrand rain hold co.ltd)
 Retaining wall design goes on with the choosing of tentative dimensions, which are then analyzed for stability and structural requirements. Since this s a trail process overall solution to the  problem may be obtained, all of which are satisfactory.
CANTILEVER RETAINING WALL
The cantilever wall is a reinforced concrete wall that utilizes cantilever action to retain step. The mass behind the wall from assuming natural slope. Stability of this wall mainly depends on the mass of the soil on the heel behind the wall.
Dimensions for a retaining wall should be adequate for structural stability and to satisfy local building code requirement.
The date shown below may be used where no other data is available but may result in a overly conservative design. The 200mm from a liberal  interpretation. of act (1966) and preferably not less than 600mm so that the proper placement concrete off or is broke off a sufficient amount will remain to satisfy structural and aesthetic require (Bowles I . E)
The base slab dimension should be such that the resultant of the vertical loads fall within the middle one third otherwise. The toe pressure will be too much such that only a part (Bowles J-E and (Hansen and Peck) of the footing will be effective.
 A better is increasing in order to save materials. A front better is more acceptable so that the forward wall movement to develop active pressure is not noticeable.
A slight increase in wall stability is usually  obtain when the battler is on the Bach face (Ref Bowles J.E) see fig 1-3 below for illustration.