The GATE Grind

GATE 2018 CE (CE1) – Question 41

Geotechnical Engineering · Deep foundations: piles and pile groups · 2 marks · Multiple choice

A 0.5 m × 0.5 m square concrete pile is driven into homogeneous clay of undrained strength 50 kPa and unit weight 18 kN/m³. Design load is 500 kN, adhesion factor 0.75 and factor of safety 2.0. Required pile length is ______.

  1. 5.2 m
  2. 5.8 m
  3. 11.8 m
  4. 12.5 m

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (C) 11.8 m

Explanation

Ultimate resistance required is $2(500)=1000$ kN. Toe resistance is $9(50)(0.25)=112.5$ kN. Shaft resistance is $0.75(50)(2)L=75L$ kN. Thus $L=(1000-112.5)/75=11.833$ m, closest to 11.8 m (C).