Which of the following is the primary reason for adopting deep foundations over shallow foundations?

Explanation:

Poor soil bearing capacity at shallow depths

• Primary reason: Deep foundations are adopted when the soil at shallow depths does not have sufficient bearing capacity to support the load of the structure.

• Explanation: When the upper layers of soil are weak or compressible, deep foundations, such as piles or drilled shafts, are required to transfer the load to more stable soil or rock layers deep underground. This ensures the stability and safety of the structure.

Additional Information 

Faster construction speed

• This is incorrect. Deep foundations generally require more time and effort to construct compared to shallow foundations, especially due to the need for drilling or piling deep into the ground.

High water table

• While a high water table can influence foundation choice, it is not the primary reason for choosing deep foundations.

• A high water table can make excavation difficult but does not necessarily require a deep foundation if the soil conditions are stable at greater depths.

Low construction cost

• Deep foundations are typically more expensive than shallow foundations due to the increased complexity and materials required, so cost is not a primary reason for choosing deep foundations.

• They are used primarily for soil stability, not cost reduction.