GATE 2018 CE (CE1) – Question 54
The proposed excavation is shown. Adjacent river level is +20 m, clay unit weight 20 kN/m³ and water unit weight 10 kN/m³. Factor of safety against sand boiling, to two decimals, is ______.
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Show answer and explanation
Correct answer: 1.00 to 1.03
Explanation
The remaining clay blanket is 10 m thick, giving downward pressure $20(10)=200$ kPa. River level +20 m sets uplift pressure at the sand surface (elevation 0) to $10(20)=200$ kPa. Safety factor is $200/200=1.00$.