Decrease the pressure exerted on the ground by increasing the area.
Explanation
The fundamental principle governing this question is the definition of Pressure, which is the force exerted per unit area. Mathematically, it is expressed as:
Pressure (P) = Thrust (F) / Area (A)
In the context of high-rise buildings, the "Thrust" is the immense weight of the structure acting downwards due to gravity. For a building to remain stable and not sink into the ground, the pressure exerted on the soil must be minimized.
Since pressure is inversely proportional to the area ($P \propto 1/A$), increasing the surface area of the foundation distributes the total weight over a larger region. This significantly reduces the pressure exerted on the ground. Conversely, a smaller area would result in extremely high pressure, potentially causing the ground to yield.
Regarding the other options:
- Increase the thrust exerted by the building on the ground. is incorrect because the thrust (total force) is determined by the weight of the building ($W = mg$), which remains constant regardless of the foundation's area.
- Increase the structural density of the foundation. is incorrect because structural density is a property of the construction materials, not a result of the foundation's geometric area.
- Reduce the total weight of the building. is incorrect because the total weight is a function of the building's mass, which does not change simply by widening the base.
Key Takeaway
Pressure is inversely proportional to the contact area. Increasing the area of a foundation reduces the pressure exerted on the ground for a given force (weight), ensuring structural stability.