Soil MECHANICS AND FOUNDATION ENGINEERING-II (CE 311) [6] Types of Foundations 1437-Summer SaMeH

6.1 Types of Foundations Shallow Foundations Mat Foundations Spread Footings Mat Foundations CE311

6.1 Types of Foundation Shallow foundations Df < B Df >> B Deep foundations Df >> B Df B Df B CE311

6.1.0 Shallow foundations Foundations at shallow depths (Df/B ≤ 1). Spreading the loads laterally. Shallow foundations are called Bases: foundations supporting machinery Footing: supports a single column Mat: supports several columns. Supported by piles or piers in deep foundations CE311

Spread footing / Isolated footing Combined footing Strap footing 6.1.0 Shallow foundations Strip footing Spread footing / Isolated footing Combined footing Strap footing Raft/mat footing CE311

6.1.2 Spread Footings General: Widely used because they are most economical. Used for buildings of light loads (1-4 Stories) and strong shallow soils. Deliver the load directly to the supporting soils. Footings can be connected together with grade beams to provide more lateral stability. Spread footings should be above the water table. As the building weight increases, the footing needs to expand in size or different systems need to be used. CE311

6.1.1 Strip footing it is a concrete structure, which runs along the entire perimeter of the house. Strip foundation recommended for waterproofing, as well as insulate them. CE311

6.1.1 Strip footing Known as continuous footing. Used for a load-bearing wall and a row of columns so closely spaced. CE311

6.1.2 Isolated footing Spread footing or pad footing is provided to support an individual column. Footing is circular, square or rectangular slab of uniform thickness or stepped or hunched. CE311

6.1.2 Isolated footing A footing that transmits a load from columns to the supporting soil. If the soil is weak or the column loads heavy, isolated spread footing  must be larger. CE311

6.1.2 Spread or isolated footing CE311

6.1.2 Spread or isolated footing CE311

6.1.2 Spread or isolated footing CE311

6.1.2 Spread or isolated footing CE311

6.1.3 Combined footing A combined footing is a long footing supporting two or more columns (in typically) two columns. A combined footing is a rectangular or trapezoidal shaped footing. CE311

6.1.3 Combined footing Supports two columns so close to each other that their individual footings would overlap. Is used when the property line is so close to one column that a spread footing would be eccentrically loaded. By combining it with an interior column A footing may be rectangular or trapezoidal in plan. CE311

6.1.3 Combined footing CE311

6.1.4 Strap (Cantilever) footing Cantilever footing. A cantilever footing or strap footing normally comprises two footings connected by a beam called strap. It is a special case of combined footing. CE311

6.1.4 Strap footing CE311

6.1.4 Strap footing Consists of two isolated footings connected with a strap beam as one unit. Is more economical than a combined footing when the soil pressure is high and the distance between the columns is large. CE311

6.1.5 Raft or Mat foundation In case of soils having low bearing capacity, heavy structural loads are usually supported by providing raft or mat foundations. CE311

6.1.5 Raft or Mat foundation Is a large slab supporting a number of columns and walls under the structure or a large part. Useful in reducing the differential settlements on soils or a large variation in columns loads. Can be used in these cases: , silts to let foundation settle without great differences. buildings of medium to heavy loads (10 to 20 stories). Light load buildings on very weak or expansive soils. where soil requires large bearing area. Expansive clays CE311

6.1.5 Raft or Mat foundation CE311