GATE 2026 MN – Question 49

Geomechanics and Ground Control · Ground Control · 2 marks · Numerical answer

A plug dam seals a3.5×2.5 m gallery. Rock–dam interfacial shear strength is1.0 MPa. Find minimum dam thickness resisting10.0 MPa water pressure, in m to two decimals.

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Correct answer: 7.00 to 7.50

Explanation

Water thrust is pressure times face area:10×3.5×2.5=87.5 MN. For thickness t, resisting interface area is perimeter times thickness=2(3.5+2.5)t=12t m². At1 MPa, shear resistance is12t MN. Equating gives t=87.5/12=7.2917 m, or7.29, under the ideal uniform-interface assumption.

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