Bligh’s creep theory for seepage under hydraulic structures: Which fundamental assumption does Bligh’s theory make about head loss along the percolation path (creep line)?

Introduction / Context:
Bligh’s creep theory is an early empirical method to estimate seepage and uplift under weirs and barrages founded on pervious soils. It models the seepage path along the contact between the structure and subsoil as a “creep line”.

Given Data / Assumptions:

• Structure on pervious foundation with upstream and downstream cutoffs/floors.
• We seek the central assumption about how head loss distributes.

Concept / Approach:
Bligh assumed the total head loss is proportional to the total length of the creep path, regardless of whether the path length is horizontal or vertical. Hence, horizontal and vertical segments are treated with equal weight in calculating creep length.

Step-by-Step Solution:
Define total creep length = sum of all horizontal and vertical contact lengths.Assume head loss distributes uniformly per unit creep length.Therefore, horizontal and vertical components contribute equally per unit length.

Verification / Alternative check:
Later theories (Lane’s weighted creep theory) adjusted this by giving different weights to vertical and horizontal creeps, recognizing limitations of Bligh’s equal-weight assumption.

Why Other Options Are Wrong:
More or less weight to horizontal creep: These characterize Lane’s approach, not Bligh’s.Sine-curve head loss: Not a Bligh assumption; it is not a sinusoidal distribution model.

Common Pitfalls:

• Mixing Bligh’s and Lane’s theories.
• Applying Bligh’s equal-weight rule to problems specifically asking for Lane’s weighting.

Final Answer:
Horizontal and vertical creep lengths are given equal weight (equal importance)