Question:

A 2 m wide strip footing is founded at a depth of 1.5 m below the ground level in a homogeneous pure clay bed. The clay bed has unit cohesion of 40 kPa. Due to seasonal fluctuations of water table from peak summer to peak monsoon period, the net ultimate bearing capacity of the footing, as per Terzaghi’s theory, will

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In purely cohesive soils, the bearing capacity is independent of water table fluctuations, as it primarily depends on soil cohesion.
Updated On: Jan 24, 2025
  • remain the same
  • decrease
  • increase
  • become zero
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The Correct Option is A

Solution and Explanation

Step 1: According to Terzaghi’s bearing capacity theory, the ultimate bearing capacity of a strip footing on clay soil is given by the formula: \[ q_u = c N_c + \gamma D_f N_q + 0.5 \gamma B N_{\gamma} \] For purely cohesive soil (clay), the bearing capacity equation simplifies to: \[ q_u = c N_c \] where \( c \) is the cohesion of the soil and \( N_c \) is a bearing capacity factor. Step 2: Since the given soil is homogeneous pure clay, the bearing capacity primarily depends on cohesion. The water table fluctuations affect the effective stress in granular soils, but for cohesive soils (clay), cohesion remains unchanged by water table fluctuations. Step 3: As the unit cohesion of the soil remains constant at 40 kPa regardless of the water table fluctuations, the net ultimate bearing capacity remains unchanged. Conclusion: The net ultimate bearing capacity will remain the same, hence the correct answer is option (A).
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