Foundation systems — identify the type: thick RCC slab covering entire building area to carry heavy concentrated loads What is the correct name for a foundation that consists of a thick reinforced cement concrete slab (mat) covering the whole plan area to distribute heavy concentrated structural loads?

Introduction / Context:
When column loads are high and soil bearing capacity is low or variable, isolated footings may overlap or become excessively large. In such cases, engineers adopt a single large slab foundation that supports multiple columns and walls, distributing loads more uniformly to the soil: the raft (or mat) foundation.

Given Data / Assumptions:

• Heavy, concentrated loads from multiple columns/walls.
• Single thick RCC slab covering nearly the entire building footprint.
• Intent is to reduce differential settlement and stress concentrations.

Concept / Approach:

A raft foundation behaves like a plate on an elastic foundation, spreading loads over a wide area and lowering contact pressure. It may include beams, ribs, or cellular voids depending on stiffness requirements. This contrasts with combined footings (serving two or more adjacent columns) and strap footings (connected by a beam to balance eccentricity), which do not cover the full area.

Step-by-Step Solution:

Verification / Alternative check:

Soil-structure interaction models and design guides (e.g., plate-on-Winkler) specifically address raft/mat foundations for such loading and soil conditions.

Why Other Options Are Wrong:

• Combined footing supports a few columns only.
• Strap footing connects eccentrically loaded footings, not entire area coverage.
• “None” is incorrect because the described system is standard as a raft/mat.

Common Pitfalls:

• Ignoring punching shear checks under columns within the mat.
• Neglecting settlement analysis and groundwater uplift in deep basements.

Final Answer:

Raft footing (mat foundation).