Concrete Structures:- Stair Case and Foundations.

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Lane’s Weighted Creep Theory

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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 (L l ) is given by L l = (d 1 + d 1 ) + (1/3) L 1 + (d 2 + d 2 ) + (1/3) L 2 + (d 3 + d 3 ) = (1/3) (L 1 + L 2 ) + 2(d 1 + d 2 + d 3 ) = (1/3) b + 2(d 1 + d 2 + d 3 ) To ensure safety against piping, according to this theory, the creep length Ll must no be less than C1H L , where H L is the head causing flow, and C 1 is Lane’s creep coefficient given in table –2 Table – ...
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Bligh’s Creep Theory for Seepage Flow

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According to Bligh’s Theory , the percolating water follows the outline of the base of the foundation of the hydraulic structure. In other words, 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. Further, it is assumed in this theory, that the loss of head is proportional to the length of the creep. If HL is the total head loss between the upstream and the downstream, and L is the length of creep, then the loss of head per unit of creep length (i.e. H L /L) is called the hydraulic gradient. Further, Bligh makes no distinction between horizontal and vertical creep. Consider a section a shown in Fig above. Let H L be the difference of water levels between upstream and downstream ends. Water will seep along the bottom contour as shown by arrows. It starts percolating at A and emerges at B. The total length of creep is given by L = d 1 + d 1 + L 1 + d 2 + d 2 + L 2 + d 3 + d 3 = (L 1 +...
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Khosla’s Theory and Concept of Flow Nets

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Many of the important hydraulic structures, such as weirs and barrage, were designed on the basis of Bligh’s theory between the periods 1910 to 1925. In 1926 – 27, the upper Chenab canal siphons, designed on Bligh’s theory, started posing undermining troubles. Investigations started, which ultimately lead to Khosla’s theory . The main principles of this theory are summarized below:          (a) The seepage water does not creep along the bottom contour of pucca flood as started by Bligh, but on the other hand, this water moves along a set of stream-lines. This steady seepage in a vertical plane for a homogeneous soil can be expressed by Laplacian equation: Where, φ = Flow potential = Kh; K = the co-efficient of permeability of soil as defined by Darcy’s law, and h is the residual head at any point within the soil. The above equation represents two sets of curves intersecting each other orthogonally. The resultant flow diagram showing both of...
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