Combined footing:
- It supports two or more columns. It may be rectangular, trapezoidal shape or T-shape.
- When the bearing capacity of soil is low, resulting a large area on footing and columns are closely spaced , then the combined foundation are constructed.
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Classification of combined footing
a) Grid foundation:
- Stripe footing provided in both direction as grid foundation
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Uses of grid foundation
- When columns are close to each other.
- More than one column rest on the one pad. It increases the capacity of foundation and can be effectively used in the medium storey buildings
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b) Mat foundation:
- For very low bearing capacity of soil, the stripes or the footings merged resulting in the mat foundation.
- It is a single large continuous footing, supported load of entire structure
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Features of mat foundation
- All the columns rest on mat of RCC slab.
- It is used in large buildings and poor soil condition.
- It minimizes unequal settlements.
- It is an expensive and used when basement/ underground floor exits.