Theory of Counterfort

Behavior of various parts of counterfort retaining wall  – (1) Design of stem  – unlike the stem of cantilever retaining wall the stem of a counterfort retaining wall acts as a countinous slab supported slab supported on counterforts. Due to the varying pressure over the height of stem slab deflects outward and hence main reinforcement is provided along the length of the retaining wall at the outer face at the outer face of the stem between the counterforts. The raction of the stem is taken by the counterforts to which it is firmly anchored. (2) Design of heel slab  – The action of heel slab is similar that of stem. The heel slab is subjected to the downward load due to weight of soil and self weight and upward load due to soil reaction. The net load is found to act downwards. The maximum net pressure is found to act on a strip of unit width near edge. If p is the net jdownward kjpressure per unit area the maximum bending moment near counterforts will be

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 (-ve) and positive bending moment will be

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. The heel

slab is firmly attached to the counterforts by means o f vertical ties. (3) Design of toe slab  – The toe slab bends as a cantilever as in the case of cantilever retaining retaining wall. Due to bending of toe as cantilever clockwise moments moments are induced which are shared by both vertical stem and heel slab. (4) Design of counterfort  – The counterfort take ractions both from the stem as well as the heel slab. These are designed as vertical cantilevers held in position by the base slab. The loading on these counterforts is due to lateral earth pressure acting on the upright slab. It can be of two types main counterfort and front counterfort.