FOOTING AND FOUNDATION GEOLOGY

footing footing is a foundations unit constructed in concrete under the base of wall or a column for the purpose of distributing the load over a large area. In colder regions, footings are placed below the frost line to prevent movement during freezing.

Types of footing Spread footing – a circular, square, or rectangular slab of uniform thickness. Sometimes it is tepped or haunched to spread the load over a large area. When the spread footing is provided to support an individual column, it is called an isolated.

Types of footing Strap footing– consist of two of two isolated footings connected together with a structural strap or a level. The strap connects the individual footings such that they behave as one unit.

Types of footing Combined footing – supports two columns. It is used when the two columns are so close to each other that their individual footings would overlap.

Types of footing Strip footing – this is another type of spread footing which is used for a load bearing wall. A strip footing can also be used for a row of columns which is closely spaced. Strip footing can also called continuous footing

Types of footing Mat/raft footing – consist of one footing base that is usually placed under the entire building area. They are used when column loads are heavy that single footings can’t be used.

Foundation Foundation is an element of architectural structure which connects it to the ground and transfer load from the structure into deep parts of the soil. It is used when the allowable bearing capacity is the soil is very low, that the footings are not enough to support the loads of a structure.

Major types of foundation Shallow foundation – a type of foundation that does not extended deep into the ground. Shallow foundation are called footings Deep foundation – are type of foundation that provides support for a structure by transferring loads to depth of 3 meters or deeper than it to the ground

Shallow foundation

Types of shallow foundation Strip foundation - is provided for a load-bearing wall. A strip footing is also provided for a row of columns which are so closely spaced that their spread footings overlap or nearly touch each other. In such a case, it is more economical to provide a strip footing than to provide a number of spread footings in one line. A strip footing is also known as continuous footing.

Types of shallow foundation Spread foundation - is provided to support an individual column. A spread footing is circular, square or rectangular slab of uniform thickness. Sometimes, it is stepped or haunched to spread the load over a large area.

Types of shallow foundation Combined foundation - It is used when the two columns are so close to each other that their individual footings would overlap. A combined footing is also provided when the property line is so close to one column that a spread footing would be eccentrically loaded when kept entirely within the property line. By combining it with that of an interior column, the load is evenly distributed. A combined footing may be rectangular or trapezoidal in plan.

Types of shallow foundation Strap foundation - A strap (or cantilever) footing consists of two isolated footings connected with a structural strap or a lever. The strap connects the two footings such that they behave as one unit. The strap is designed as a rigid beam. The individual footings are so designed that their combined line of action passes through the resultant of the total load. a strap footing is more economical than a combined footing when the allowable soil pressure is relatively high and the distance between the columns is large.

Types of shallow foundation Mat/raft foundation - A mat or raft foundation is a large slab supporting a number of columns and walls under the entire structure or a large part of the structure. A mat is required when the allowable soil pressure is low or where the columns and walls are so close that individual footings would overlap or nearly touch each other. Mat foundations are useful in reducing the differential settlements on non-homogeneous soils or where there is a large variation in the loads on individual columns.

Deep foundation

Types of deep foundation Pile foundation – are made of long cylindrical strong materials, such as concrete, that is pushed into the ground so that structures can be supported on top of it.

Classification of piles with respect to load transmission and functional behavior end bearing pile – the bottom end of the piles rests on a layer of strong soil or the bed rocks. The load is transferred through the pile into the strong layer, making the pile act as a column with the strong layer of the ground as its base.

Classification of piles with respect to load transmission and functional behavior Friction pile – a load bearing pile that receives its vertical support from skin friction between the surface of the buried pile and the surrounding soil.

Classification of piles with respect to load transmission and functional behavior Combined bearing and friction pile – transfers loads of the structure though side friction and end bearing.

Classification of piles with respect to load transmission and functional behavior Compaction pile – a group of piles driven into the ground to compact the soil and increase its bearing capacity.

Classification of piles with respect to material timber – is used from earliest record time and still used for permanent works in regions where timber is plentiful. Timber is most suitable for long cohesion piling and piling beneath embankments

Classification of piles with respect to material concrete – it can be divided to pre-cast and cast-in place concrete piles: pre-cast concrete piles – it is formed and reinforced in a high-quality controlled concrete. Usually used of squared, triangle, circle, or octagonal section, they produced in a short length in one-meter interval between 3 and 13 meter. Cast in place concrete piles – are the most type commonly used for foundation due to the great diversity available for pouring concrete and the introduction of the pile into the soil. 

Classification of piles with respect to material Steel piles – made of sectors in the form of H, X or of thick pipes. They are suitable for handling and driving in long lengths.

Classification of piles with respect to material Composite piles – is combination of different materials in the same of piles.

classification of piles with respect to effect on the soil Driven piles – are considered to be displacement piles. In the process of driving pile into the ground, soil moved radially as the pile shaft enters the ground.

classification of piles with respect to effect on the soil Bored piles (replacement piles) – are generally considered to be non-displacement piles aa void is formed by boring or excavating before piles is produced. Piles can be produced by casting concrete in the void.

classification of piles with respect to effect on the soil Cast-in-situ (drilled) – these piles are constructed by drilling holes in the ground to required depth and then filling the hole with concrete. Reinforcement are also used in concrete as per the requirements.

Types of deep foundation Piers – pier foundation is a grid system of girders (beams), piers, and footings used in construction to elevate the superstructure above the ground plane or grade. The piers serve as a column for the superstructure.

Types of deep foundation Caissons – is hollow substructure designed to be constructed on or near the surface and then sunk as a single unit to their required level.

Types of caissons Open caissons – in open caissons or well foundations the top and bottom are kept open during construction. The caisson is sunk in place as grab buckets through water remove soil. Upon reaching its final position a concrete seal, usually 1.5 m to more than 4.5 m thick, is deposited through water.

Open caissons Advantages of Open Caissons- The advantages of open caissons are their feasibility to be sunk to great depths. Their construction cost is relatively low. Disadvantages of Open Caissons- The disadvantages of the open caissons are that the bottom of the caisson cannot be thoroughly cleaned and inspected. The concrete seal placed in water is not satisfactory and soil near the cutting edge may require hand excavation by diver. If obstruction like boulders or logs are encountered the construction gets slowed down.

Types of caissons Pneumatic caissons – a type of caisson where it is sealed at the top and is open at the bottom. The water is excluded from the chamber by means of compressed air and to help workers put the concrete inside the chamber

Pneumatic caissons Advantages of Pneumatic Caissons-  The advantages of pneumatic caissons are that all work can be done in dry and there is control over work. The foundation is prepared better and plumpness of caissons is easier to control. The concrete placed in dry condition will have good and reliable quality. The obstruction from boulders and logs can readily be removed and excavation by blasting may be done if necessary. Disadvantages of Pneumatic Caissons- Pneumatic caissons have high cost of construction. They cannot be sunk to depths greater than 35 m because the higher pressure below this depth cannot be resisted by human body.

Types of caissons Box caissons – the box caissons are closed at the bottom and open at the top They are usually fabricated on land, floated to site and sunk in position. While sinking sand, gravel, concrete or water are filled inside the caisson. This type of caisson is suitable when hard strata are available at shallow depth. Sometimes false bottom made out of wooden planks are also used for floating.

Box caissons Advantages of Box Caisson- The advantages of this caisson is its cost of construction. It is used when construction of caissons at site not feasible or costly. Disadvantages of Box Caisson- The disadvantages of this type of caisson are that the bearing strata should be level or made level. This type is feasible only when suitable bearing stratum is available at shallow depth. Provision should be made for scour protection. The bearing stratum is often not compact.

Importance of footing and foundation Footing and foundations are made to keep the structure still, or to prevent settling unevenly It also prevents the structure from moving in areas where frost occurs. this is common in areas that experiences low temperature or winter. Without footing or foundations, a structure may either sink into the ground once loads are applied to it, or it may also collapse, the idea is column and walls by themselves without the help of footings and foundations.

DIFFERENCE BETWEEN FOOTING AND FOUNDATION According to Karl von Terzaghi, a foundation is shallow if its depth is equal to or less than its width. Foundations constructed by open excavation are also called shallow foundations. The term footingis used in conjunction with shallow foundations commonly.