Bligh's creep theory is used for the design of

Concept:

Bligh's Creep Theory:

• Bligh assumed that the percolating water follows the outline of the base of the structure which is in contact with the subsoil. 
• The length of the path traversed by the percolating water is called the length of creep or creep length. The total head H is lost in the creep length L at a uniform rate.
• He further assumed that the head loss per unit length of creep (i.e. H/L) which is called hydraulic gradient is constant throughout the percolating passage i.e. Loss of head is proportional to the length of the creep.
• The reciprocal of hydraulic gradient (i.e. L/H) is known as Bligh's creep coefficient.
• Bligh did not differentiate between horizontal and vertical creep, Consider a horizontal impervious floor with three vertical cutoffs.
• The seepage water will then follow the path indicated by arrows and the creep length.

L = b + 2d₁ + 2d₂ + 2d₃

Hence option (2) is the correct answer.