Test: Lane’s Weighted Creep Theory - Civil Engineering (CE) MCQ

A weightage factor of 1/3 is proposed by Lane for horizontal creep and 1.0 for vertical creep. The weighted creep length –
L = (1/3) B + V where B = sum of horizontal contacts and sloping contacts less than 45° to the horizontal and V = sum of vertical contacts and sloping contacts greater than 45° to the horizontal.

A weir with three sheet piles is shown below. The seeping path of the water along the bottom contour of the structure is also shown with arrows.

Here, d₁, d₂ and d₃ are the depth of upstream, intermediate and downstream sheet piles respectively. b is the total length of the weir floor.
Bligh's Creep Theory for Seepage Flow:

• According to Bligh's Theory, seeping water creeps along the bottom contour of the structure. The length of the path thus traversed by water is called the length of the creep.
• According to Bligh’s Theory from the diagram, the creep length is given by,

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 suggested a weighting factor of 1/3 for the horizontal creep, as against 1.0 for the vertical creep.
• According to Lane’s Theory from the diagram, the creep length is given by,

Lane's  Weighted Creep Theory: Lane's concluded that horizontal creep is less effective in reducing uplift than vertical creep. Therefore, he suggested a factor of 1/3 for horizontal creep against 1 for vertical creep.
Assumptions:

• Slopes steeper than 450 are taken as verticals(d)
• Slopes less than 450 are taken as horizontals(l)

Creep length

Safe creep length
L = C.H
C = Lane's coefficient 

Bligh calculated the total length of creep by adding the vertical and horizontal creep together. Lane proposed horizontal creep is less effective in reducing uplift and introduced the weightage factor for the same.

For very fine sand or silt, the value of Lane’s coefficient is 8.5. For fine sand and coarse sand, the value is 7.0 and 5.0 respectively. Also, the safe hydraulic gradient should be less than 1/7 and 1/5 for fine sand and coarse sand respectively.

For clayey soils, the range is 1.6 to 3.0. For boulders, gravel, and sand it is 2.5 to 3.0 and for gravel and sand, the range is 3.0 to 3.5.