When braced cut passes through layers of both sand and clay(fig-), an equivalent value of cohesion (assume = 0) is determined using the peck(1943) eq. :

Where H= Total height of the cut, = Unit weight of the sand, = Height of the sand layer, = a lateral earth pressure coefficient ( = 1). = angle of friction of sand, = Unconfined compressive strength of clay, n'= a coefficient of progressive failure (average value 0.75).

The equivalent unit weight of the layer is determined from the equation:

Where = Saturated unit weight of clay layer.

Now N value is calculated by