IN CASE THE LENGTH OF RETAINING WALL EXCEEDS 45 METRES EXPANSION JOINT SHOULD BE PROVIDED.

GENERAL DESIGN REQUIREMENTS TO AVOID FAILURE OF THE RETAINING WALLS:-- Following Requirements must be satisfied to avoid the failure of the Retaining walls (1) The factor of safety against sliding should be at least 1.5 if the passive resistance of the soil in front of the wall is neglected as it is possible that the soil is removed by the constructional operation ,scour etc .The factor of Safety against sliding should be taken 2 if the passive resistance of soil is taken into consideration .(2) A factor of safety of 1.5 should be maintained against the overturning.The bearing pressure at the toe should be with in permissible limits. (3) The thickness of stem , heel and toe should be adequate to resist the bending moments and shear force to which they are subjected .(4) Construction joints should be provided between base slab and upper portion of the wall ,and should be capable of resisting the shear force caused by the lateral pressure above the joint. Various types of construction joints are required to be resisted by the key and the dowel bars .If the length of the Retaining wall exceeds 45 metres expansion joints should be provided .The spacing of these joints depends on the temperature variation , exposure to weather and the time and season of laying the concrete ,however in no case should the spacing of these joints exceed 45 metres. CHOICE OF TYPE OF RETAINING WALL :-- In RCC construction generally either Cantilever wall is used or Counterfort wall is used .Whether a Cantilever type of wall is economical depends upon several factors , main factor however being the height of the wall .Relative cost of steel , concrete and form work and intensity of earth pressure also have a bearing on the choice of the type of wall . Cantilever type wall is preferable where skilled labour is not available as the construction is simpler in this case and the placing of steel is much easier.In the case of Counterfort retaining walls the cost of form work is more and placing of the steel is complicated .In general Cantilever type of retaining wall can be used for height up to 6 metres.