Lane’s Weighted Creep Theory

Bligh, in his theory, had calculated the length of the creep, by simply adding the horizontal creep length
and the vertical creep length, thereby making no distinction between the two creeps. However, Lane, on
the basis of his analysis carried out on about 200 dams all over the world, stipulated that the horizontal
creep is less effective in reducing uplift (or in causing loss of head) than the vertical creep. He, therefore,
suggested a weightage factor of 1/3 for the horizontal creep, as against 1.0 for the vertical creep.

Thus in Fig–1, 

the total Lane’s creep length (Ll) is given by

Ll = (d1 + d1) + (1/3) L1 + (d2 + d2) + (1/3) L2 + (d3 + d3)
= (1/3) (L1 + L2) + 2(d1 + d2 + d3)
= (1/3) b + 2(d1 + d2 + d3)

To ensure safety against piping, according to this theory, the creep length Ll must no be less than C1HL,
where HL is the head causing flow, and C1 is Lane’s creep coefficient given in table –2

Table – 2: Values of Lane’s Safe Hydraulic Gradient for different types of Soils



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