To ensure uniform pressure distribution, the thickness of the foundation, is

ANS:C - decreased gradually towards the edge

To ensure uniform pressure distribution, it's essential to consider the distribution of loads and the response of the foundation to those loads. The objective is to prevent excessive differential settlement and to maintain stability. The most common approach to achieve uniform pressure distribution in a foundation is to increase the thickness of the foundation gradually towards the edge. Here's why:

1. Load Distribution: Structures exert loads on the foundation, which need to be distributed uniformly to prevent localized bearing capacity failures. By increasing the thickness towards the edge, the foundation can better spread out the load over a larger area, reducing the pressure exerted on the soil and minimizing the risk of settlement.
2. Soil Mechanics: Soil near the edges of the foundation experiences higher stresses compared to the central portion due to the 'bulging effect'. Increasing the thickness towards the edges helps compensate for this effect, ensuring that the soil experiences similar stresses throughout.
3. Stability: A foundation with a tapered thickness, thicker towards the edges, provides better stability against overturning and sliding. This is particularly important in situations where the foundation is subjected to lateral loads or where there's a risk of uplift.
4. Uniform Settlement: Gradually increasing the thickness towards the edge promotes more uniform settlement of the foundation, reducing the potential for differential settlement that can lead to structural damage.

Keeping the thickness uniform throughout or decreasing it towards the edge wouldn't effectively address the issues related to load distribution, stability, and uniform settlement. Keeping the thickness zero at the edge would result in inadequate support and potentially lead to structural failure.