This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Seepage Theories – Lane’s Weighted Creep Theory”.
1. Lane’s in his theory proposed that horizontal creep is more effective than the vertical creep.
Explanation: He proposed that horizontal creep has less head and is less effective in reducing uplift than vertical creep. A weightage factor of 1/3 is proposed for horizontal creep and 1.0 for vertical creep.
2. In Lane’s weighted creep theory, he suggested a weightage factor _________
a) 1/3 for horizontal creep and 1.0 for vertical creep
b) 1/3 for vertical creep and 1.0 for horizontal creep
c) 2/3 for horizontal creep and 1/3 for horizontal creep
d) 2/3 for vertical creep and 1/3 for horizontal creep
Explanation: 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.
3. Which of the following limitation of Bligh’s theory forms the basis of Lane’s creep theory?
a) No distinction between the vertical and horizontal creep
b) No distinction between effectiveness of outer and inner faces of sheet pile
c) Significance of exit gradient is not considered
d) Bligh’s theory holds good when the length of the horizontal floor is greater than or equal to twice the depth of the deepest pile
Explanation: 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.
4. What is the value of Lane’s coefficient for fine sand and coarse sand?
a) 7 and 5
b) 5 and 7
c) 7 and 8.5
d) 7 and 9
Explanation: 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.
5. What is the range of Lane’s coefficient for clayey soils?
a) 3.0 to 3.5
b) 2.5 to 3.0
c) 1.6 to 3.0
d) > 3.0
Explanation: 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.
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