The friction circle method is based on the assumption that the resultant reaction along a slip surface is tangential to a circle of radius

Friction circle method:

This method is also based on total stress analysis in which shearing angle of ϕ is used to analyse the stability of finite slope.

The principle of the method is that the inter granular forces are in an obliquity of ϕ to the circular surface at failure, where ϕ is the angle of the internal friction of the soil.

When the length of the arc is divided into small elements, the line of action of the inter granular forces acting on these elements can be defined by a tangent to the friction circle drawn around the centre of the sliding circle.

The radius of this friction circle is given by R sinϕ

Where,

R is the radius of the sliding circle.

Thus, the friction circle is agraphical tool that defines the line of action of the intergranularforces at any given point on the sliding circle in a convenient way.In geotechnics, the method is used primarily for slope-stability investigations in homogeneous soil when both cohesive and frictional components have to be considered.