Pile Foundations

PILE FOUNDATION:

Pile foundations are the most commonly used deep foundation. They consist of spread/grillage footing, supported on piles that go deep down up to the depth where a good bearing stratum is available. Pile foundations are used in the following situations:

1. When the topsoil has a poor bearing capacity and the shallow footing is not suitable, because the stratum of required bearing capacity is at a greater depth.

2. When the soil is waterlogged.

3. When the structural load is heavy and uneven.

4. When there is a danger of scouring action of water, as in the case of structures to be constructed on the river bed or near the seashore.

CLASSIFICATION OF PILES:

Piles are classified based on the following criteria:

(1) Based on the function.

(2) Based on the material of construction.

Classification Based on the Function Depending upon the function or the use, piles may be classified as follows: 

1. Bearing Piles:

Bearing piles are those piles that transfer the load, through weak/soft soil or water, to a suitable hard stratum. These piles are driven into the ground until a suitable hard stratum, having the required bearing capacity, is reached. These piles do not take any load themselves, but only transfer the load to the stratum, by bearing at the end.

Fig 2.11 Bearing Piles

2. Friction Piles:

Friction piles transfer the load by the friction (skin friction) developing along the surface of the pile and the surrounding soil. These piles are used in weak or soft soils when a suitable hard stratum is not available at an appropriate depth. These piles are also called floating piles.

3. Friction Cum Bearing Piles:

These piles transfer the load by bearing as well as friction. These piles rest on a hard stratum. These piles are used when the bearing capacity of the available hard stratum is less than the load coming on the piles. 

4. Compaction Piles:

Compaction piles are used to compact the loose granular soils. These piles result in an increase in the bearing capacity of the soil. They may be made up of weaker material as the pile does not carry any load itself but only compacts the soil.

5. Sheet Piles:

Sheet piles are used to retain soil. They act as retaining walls to support the soil laterally which may come out under pressure. Sheet piles are also used to prevent leakage/seepage by providing an impervious layer. These piles do not take or transfer any load. These are also used to prevent erosion of river banks or to retain the sides of foundation trenches.

6. Anchor Piles:

Anchor piles provide support against the horizontal force from sheet piling, piles, or other earthwork embankments.

7. Batter Piles:

These piles are driven at an inclination to resist large horizontal or inclined forces.

8. Fender Piles:

These piles are used to protect waterfront structures from the impact of ships. These piles are generally made up of timber.

Classification of Piles Based Upon Material of Construction Based upon materials of construction, the piles are divided into the following types:

(1) Steel Piles

(2) Cement concrete piles

(3) Timber piles

(4) Sand piles

(5) Composite piles

Steel Piles:

Steel piles are used for transferring heavy loads through soft soils to deep strata. These piles require heavy equipment and machines for driving. These piles should be surface treated or encased to prevent corrosion. Steel piles are available in various shapes such as pipes, boxes, rolled steel sections, etc.

(i) Steel Pipe Piles:

Their pipes are driven into the soil to the required depth and cleared from the soil inside. After that, the pipes are filled with cement concrete. These pipes are used for transferring heavy loads to deeper depths, through soft soil, where proper bearing stratum is available.

(ii) Rolled Steel H-beam Piles:

This type of pile consists of a rolled steel H-section which can be driven easily into the soil. They are useful for deep penetration and can be lengthened as per the requirement. These piles can be used for retaining walls, bulkheads, bridges, etc.

Cement Concrete Piles:

Cement concrete has high compressive strength which makes it suitable as a pile. These piles are strong and durable and can be cast in any size.

Concrete Piles may be further classified into the following types:

(1) Precast Piles

(2) Cast in Situ Piles

(3) Prestressed Concrete Piles

(1) Precast Piles:

These types of piles are manufactured in the factory and brought to the site and driven into the ground. These are made up of reinforced cement concrete and are available in many shapes. such as square, rectangular, circular and octagonal, etc. Precast piles are available in lengths up to 30 m and diameter ranging from 400 mm to 650 mm. The reinforcement bars are placed longitudinally in the concrete and are tied with lateral reinforcement, 5 mm to 10 mm in diameter. The main bars (vertical reinforcement) are of 20 mm to 40 mm diameter and are placed at least one at each corner of the piles. The bars are protected with a concrete cover of 50 mm. These piles are provided with a steel shoe at the end which not only protects it but also helps in driving the pile into the ground.

(2) Cast in Situ Piles:

Cast in situ pile is constructed at the site in its location. They are of two types:

(a) Driven piles

(b) Bored piles

(a) Cast in situ driven piles:

This type of pile is constructed by driving a steel tube or casing into the ground having an internal diameter equal to the diameter of the pile. The tube is driven with the help of pile driving equipment. The concrete is poured into the tube, after putting the required reinforcement cage into the tube. The tube/casing provided may be removed or left in its place. If the casing is removed it is called an uncased pile, but if it is allowed to remain in its place it is called a cased pile. Figure 2.12 shows the construction of a driven cast in situ pile.

Fig. 2.12

Other types of cast in situ (driven) piles are available in the market under various trade names, some of which are listed below:

(1) Simplex pile

(2) Raymond pile

(3) Mc-Arthur piles 

(4) Franki pile

(5) Vibro pile

(b) Bored Piles: 

Bored piles are constructed by forming a borehole in the ground and then filling it with concrete. These piles may be cased or uncased. No heavy pile driving instrument is required for these piles. Bored piles are used when the hard-bearing strata is too deep to be reached by driven piles. Bored piles also have an advantage over driven piles in that they are not subjected to any kind of vibrations.

Bored piles are of three types:

(1) Pressure piles

(2) Under reamed piles 

(3) Compaction Piles

(i) Pressure Piles: 

Pressure piles are constructed by sinking a steel tube with the help of auger boring and compressed air. These piles are used in places where it is not possible to use pile driving equipment.

(ii) Underreamed Piles: 

Under reamed piles are bored concrete piles which have one or more enlarged portions, near the base, called bulbs. The bearing capacity of such piles is increased by increasing the number of bulbs. They are constructed with the help of under-reaming tools.

These piles are the safest and economical foundation in black cotton soil or expansive soils. When this pile has one bulb it is called a single under the reamed pile and if it has more than one bulb, then it is called a multi under the reamed pile. Figure 2.13 shows a single under-reamed pile.

Fig. 2.13.

(iii) Compaction Piles: 

These piles are just like under-reamed piles but with a difference that the reinforcement cage is not put in the borehole before concreting. After the concreting, the reinforcement cage is driven into the fresh concrete, causing compaction of the concrete. Their load carrying capacity is more than under-reamed piles. These piles are used in the case of loose sandy soils.

Prestressed Concrete Piles:

Prestressed concrete piles are precast into the factories and are lighter in weight as compared to precast concrete piles. These piles are manufactured just like the RCC piles but with the difference that the reinforcement cables are prestressed. These piles are lighter in weight and durable as compared to RCC piles. They have higher load carrying capacity also. Due to these reasons, prestressed concrete piles have become very popular nowadays.

2.8.2.3. Timber Pile:

Timber pile is made from the stem of a hardwood tree like sal, teak, semul, deodar, chir, and babul, etc. These piles are provided with a cast-iron shoe at the bottom. The commonly available size of the pile is 30 to 50 cm in diameter. In order to protect the head of the pile during pile driven an iron ring is fixed at the top. 

These piles are cheap and can be easily driven into the ground. Timber piles, treated with creosote oil are commonly used for marine works or when subsoil water is present. These piles transfer the load by developing skin friction between the pile and the ground soil. These piles are light and economical and used for small loads.

2.8.2.4. Sand Piles:

Sand piles are made by filling sand in boreholes. The top of the sandpile is covered with concrete. These piles are suitable for taking lighter loads only. These are generally used in road embankments. Figure 2.14 shows a sand pile.

Fig. 2.14

2.8.2.5. Composite Piles:

Composite piles are made up of more than one material. For example timber and concrete or concrete and structural steel sections. Figure 2.15 shows a timber and concrete composite pile having a lower timber portion and an upper portion of concrete.

Fig 2.15

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More types of Foundations.

 (3) Concrete Column Footing:

Column footing may be isolated (for single column) or combined (for more than one column) It is made up of reinforced cement concrete and hence called RCC footing, RCC footing is used for columns and walls carrying heavy loads or at the places where the hearing capacity of the soil is low. This footing can be square, rectangular or circular. It may be of uniform thickness or sloped as shown in Fig. 2.5. This type of footing is constructed over an 80 mm thick layer of lean concrete. The minimum thickness of RCC footing is 150 mm Reinforcement in the form of bars is placed near the bottom face of the footing in both directions as shown in Fig. 2.5.

Fig 2.5 R.C.C Foundation.

(4) Inverted Arch Footing:

Inverted arch footing is used in bridges, reservoirs, or support for drainage lines. It is not used in buildings. This footing provides a larger area for the distribution of superstructure load to the soil as shown in Fig. 2.6.

Fig. 2.6 Inverted Arch Foundation.

In this type of footing, special attention is given to strengthening the end pier by constructing a buttress that can counter the horizontal thrust transmitted by the end arch to the end pier. Inverted arch footing has the advantage that the depth of foundation is greatly reduced, especially in the case of soft soils. These footings are not used nowadays because of their skilled construction.

2.4.2. Combined Footing:

A combined footing is provided for two or more columns together under the following circumstances:

1. When one of the columns is located near the property line and the individual footings of the columns may extend outside the property line.

2. When the individual footings of the columns overlap each other due to proximity.

3. When the required area of an individual footing is more due to low bearing capacity of the soil.

This footing maybe rectangular if the two columns carry equal loads and trapezoidal if columns carry unequal loads as shown in Fig. 2.7.

Fig .2.7 Combined Foundation.

    2.4.3. Raft Foundation:

    It is a type of shallow foundation which is most suitable for heavy structures to be built on soft and marshy soil types which can cause differential settlement of the building. The Raft foundation consists of R.C.C slab covering the entire area or a slab with beams above it. It is also known as mat foundation because RCC slab covers the entire area under the structure like a mat. It is similar to an inverted beam and slab system. Raft foundation also provides a very wide area for dispersion of structural load thus reducing the intensity of pressure considerably. This results in a reduction in the overall settlement of the building.

    2.4.4. Grillage Foundation:

This type of foundation is used only when the loads are very heavy and the soil is poor Let suppose. the bearing capacity of the soil is very low. This type of footing is much lighter and does not require deep excavation. Based upon the type of material used, the grillage foundation is of the following two types:

    2.4.4.1. Steel Grillage Foundation:

This type of foundation consists of rolled steel joists or steel beam embedded in the cement concrete. The rolled steel joists (RSJ), known as grillage beams, maybe provided in one tier or two tiers depending upon the intensity of load to be transferred. The depth of this foundation is limited to 1 to 15 m. This type of foundation is constructed as follows:

(a) The foundation is excavated to the required depth, the soil is rammed and compacted well.

(b) A concrete bed of 150 mm thickness is laid and compacted well.

(c) When the concrete bed is hardened then the first tier of grillage beams is put on the bed using spacer bars to keep the beams in position.

(d) Now the second tier of beams is put over the first tier but at right angles to the first tier.

(e) The entire space is now concreted with a minimum cover of 100 mm on all the sides of the beams. 

Figure 2.9 shows a steel grillage foundation for a steel stanchion.

    2.4.4.2. Timber Grillage Foundation:

This type of foundation is used for soils and timber beams. This type of foundation is used for soils that always remain water-logged. It consists of timber planks and timber beams. This type of foundation is constructed on a timber platform rather than a concrete block. The timber platform is made up of timber planks of 50 mm to 80 mm in thickness, placed side by side. Timber beams of size 100 mm x 120 mm are placed over the timber platform covering its full length and breadth. A heavy log of suitable dimension is placed in the center over the timber beams and the timber column is constructed above this log. The load transfer path for such a footing is as follows:

Deep Foundations

Introduction:

    The foundations that are constructed sufficiently below the ground level are called deep foundations. The depth of the deep foundation is very large as compared to its width. Deep foundations are required to be constructed in any of the following conditions:

1. The bearing capacity of topsoil is very poor and the strata of good bearing capacity deep. So the foundation has to be taken deep into the ground and unevenly distributed.

2. The structural load is heavy and unevenly distributed.

3. For structures constructed on the seashore or river bed (bridge piers), where there is the possibility of scouring action of water. In these cases, the foundation must be placed below the scouring depth, even if the suitable bearing stratum is available at shallow depth.

4. If the underground water level is high or fluctuating and it is difficult or uneconomical to pump the water from the open trenches of the shallow foundation. 

Deep foundations are of the following types:

(a) Pile foundation

(b) Pier foundation.

(c) Caisson or well foundation.

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Main Components of a Building

Building components includes the following main parts :

• (a) Substructure

• (b) Superstructure

Building components in both sub-structure and super-structure are as below :

1. Foundation

2. Plinth

3. Walls

4. Columns

5. Floors

6. Sills, lintels, and sheds

7. Doors, window, and ventilators

8. Roofs

9. Stairs, lifts, ramps

10. Building finishes

11. Utility fixtures or services

Building components of sub-structure includes:

Foundation-Structure:

The first and main building components include Foundation. Which is the main part of the building and in direct contact with the subsoil. Foundations are the important part that transmits all the load to the subsoil. A proper design foundation should transfer the loads to the subsoil, in such a way that the soil should not fail and the settlement should be within the permissible limits. The nature of the foundation depends on the type of soil. In the case of load-bearing walls, a spread footing may be designed. In the case of frame structures, rafts or piles may be the better option.

Cross Section of a building

Plinth: 

        The part of the building structure between the ground level and the top of the floor level immediately above the ground is known plinth. The plinth height is such that there is no possibility of rainwater entering the ground floor of the building.

The area measured at the plinth level known as the plinth area. The height of the plinth level should not exceed 45 centimeters.

Building Walls Structure:

        Walls are constructed to enclose or occupy a required space. Walls provide security, privacy, and protection from the weather. sun, rain, and cold. The walls divide the space so that maximum carpet area and minimum area of circulation are available. Building walls construct with bricks, stones, concrete blocks that are bound together with mortar and RCC.

Building components of a walls structure:

Types of building walls :

(i) Load-bearing walls.

(ii) Non-load bearing walls.

Load Bearing Building Walls:

Load-bearing walls are those walls that support the weight of a whole building.

Non-Load Bearing Building Walls :

Non-load bearing walls are those walls that support their own weight only and do not support the superimposed load of the structure, they act as partition walls only.

Columns :

Columns are vertical compression members which transfer the superimposed load from, the beams floors/roofs to the foundation, Based upon the material of construction, the columns may be classified as brick, RCC, PCC columns, etc. They are also classified based on their shapes such as a square, rectangular and circular, etc.

Column bearing loads

Floors : 

        Floors divide a building into different levels to create more accommodation on a given plot of land. The floor above the ground level is the ground floor. The floor below the ground floor is called the lower ground floor or basement. The function of the floor is to give a firm, rigid, dry, and even platform for the occupants of the building and for the furniture, fixture, and equipment, etc.

Building components of super-structure

A floor consists of the following two basic parts:

1. Subfloor

1. Flooring

Main Building Components

The subfloor:

The subfloor is the structural part that provides the strength and stability to support the superimposed load.
The second part of the flooring is a layer providing as per the desired specification for giving a suitable floor finish.

Sills, Lintels, and Sheds:

    Sills are provided between the bottom of the window and the top of the wall below in which the window is provided.

    The lintels are provided, over any kind of openings in walls such as windows, doors, and ventilators.

    Lintels support the weight of the wall above the openings.

    Sunshades and sheds are to protect the doors, windows, and ventilators from rain.

Doors, Windows, and Ventilators:

    Doors are necessary for a building to permit free movement inside and outside of the building. It is a movable component that fits in an opening in the wall. A door frame and a door shutter. 

    The door frame is fixed to the wall and the shutter is movable. Doors may open on the side, slide, fold, or any other type. Doors are of many materials like wood-plastic (PVC), steel. aluminum etc.

    The windows and ventilators are provided in the buildings for daylight, vision, and ventilation. Just like doors, windows also have a frame and shutter.

    The frame may be made up of any material like wood, steel, aluminum, etc., but the shutters are generally made up of transparent material like glass the number of windows and ventilators is calculated as per the requirements of the particular type of building and size of rooms.

Roofs:

    A roof is the topmost part of a building that provides shelter to keep out rain, snow, sun, and wind and to protect the building from its adverse effects. Roof decking supports the roof covering and its type depends upon the location of the building, weather conditions of the site, and funds available. Many types of roof decking naming flat slabs, pitched, dome-shaped, and shell structures, etc. are different types of roofs.

The purpose of providing a roof coating on the roof deck is to protect the building from all-weather effects. The roof coating is of various types, such as tiles, thatch, corrugated sheets, slates, etc. The choice depends upon the type of building, its location, and the type of roof decking.

For example:

In the case of flat roofs. the roof covering may consist of lime concrete and mud called terracing. The roof covering on the pitched decking may be in the form of tiles, slates, or sheets (asbestos, galvanized iron, etc.). The roof covering should be carefully constructed by giving a suitable slope for proper drainage of rainwater.

Stairs:

    Stairs are used for vertical movement inside the building structure, across various levels. The stairs, lifts, ramps, and escalators, etc., also utilize for the same purpose. A staircase is series of steps at a suitable distance that connects one floor to another. The design and planning of the staircase should aim to provide quick and comfortable movement to the user. Stairs are of many types e.g straight stairs, dog-legged stairs, open newel, circular, spiral, etc.

Building components used in structure Finishes:

    Building finishes are used to give a cosmetic and decorative touch to the building. They also provide a protective covering to the surface of the building, against the adverse effects of weather, Building finishes include the following items :

• Plastering

• Pointing

• White/color washing

• Painting

• Varnishing and polishing

• Distempering etc.

        Plastering is done on the walls, columns, and other surfaces by providing a thin layer of plaster made up of materials like cement, sand, and lime, etc.

        Pointing is done to finish the mortar joints in brick or stone masonry Painting, varnishing, and polishing is done on doors, windows, shelves, and all wood and steel items for durability.

        Whitewashing, color washing, and distempering are done to protect the surfaces against the weather and give a beautiful appearance.

Utility Fixtures or Building components and Services:

    Building services include services like electricity, water supply drainage, sanitation, air conditioning, ventilation, fire control, etc. These services should be designed and provided as per the provisions of the national building code and the provisions of the municipal bodies.

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Main Components of a Building (part 2)

4. Columns:

    Vertical compression members transfer the superimposed load from, the beams/roof to the foundation, based upon the material of the construction. The columns may be classified as brick, RCC, PCC. The columns also classified on the basis of their shape such as square or rectangular and circular Etc. 

5. Floors:

        In two different levels to create more accommodation on the given plan of the land. The floor immediately above the ground level is called as ground floor and the floor above the book is called the upper floor or first floor. The floor below the ground floor is called as lower ground floor or basement the function of the floor is to give a firm rigid, dry, and even platform for the occupants of a building and for the furniture fixture and equipment.

                The floor consists of the following two basic parts;

1. Sub-floor

2. Flooring 

    The subfloor is the structural part that provides the strength and stability to support the superimposed load. the second part of the flooring is a layer provided as per desired specification suitable for the floor finish.

 

6. Sills, lintels, and sheds:

                They are provided between the bottom of Windows and top of walls below in which Window is provided the lintels are provided above any kind of opening in walls such as Windows, doors, and ventilators. Lintels support the weight of a wall above the opening.

7. Sheds:

But the shutters are generally made up of transparent material like a glass of numbers of windows and ventilators are calculated as per the requirement of a particular type of building and the size of rooms. Sunshades are limited to protect the door Windows ventilators from rain, sun, frost, and wind.it is made up of glass, fiberglass, and steel sheets.

        

8. Doors:

Doors are necessary for a building to permit free movement i.e. inside and outside of a building. It is an open-able component that is fitted into an opening in the wall. It has two parts i.e. a door frame and frame shutter.

9. Door frame: 

                 The door frame is fixed to the wall and shutters are movable. Doors are made of many materials like wood, plastic (PVC) aluminum, etc. The windows and ventilators are provided in the building for daylight, vision, and ventilation just like doors. Windows also have a frame and shutters the frame may be made up of any material like wood, steel, aluminum, etc. 

10. Building finishes:

    Building finishes are used to give a cosmetic and decorative Touch to the building. They also provide a protective covering to the surface of a building,  against the adverse effect of weather. Building finishes include the following items;

Plastering:

Pointing:

Whitewashing, Varnishing, Polishing, Painting, and Distempering Etc:

Plastering is done on walls, columns, and other surfaces by providing a thin layer of plaster made up of materials like cement, sand and lime Etc. Pointing is done to finish the mortar joints in bricks or stone masonry. Varnishing and polishing are done on doors, windows, shelves and all wouldn't steal items for durability. Whitewashing, color washing, and distempering are done to protect the surfaces against the weather and give a beautiful appearance.

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Classification Of Buildings

Buildings: 

The Buildings have many types however I've just discussed the building structures which are constructed in Pakistan, India, and Afghanistan.

Residential Buildings:

         As per BCP, the building used for residential purposes is known as a residential building. The room must provide sleeping accommodation and with or without cooking or dining facilities or both.

Residential Building:

Buildings may further be divide into types which are as follows:

1. Lodging or rooming houses.
2. One or two-family private dwellings.
3. Dormitories.
4. Apartment houses.
5. Hotels.

 Educational Buildings:

The educational buildings are those buildings that are only used for a school or college or Recognized by the appropriate Board or University. Or any other Competent Authority involving assembly for instruction or education. Including a building for such other uses as a research institution.

 Institutional Buildings:

         This group includes the building constructed by Government. These buildings are for medical, other treatment for cultural, care of persons suffering from physical or mental illness. Correctional detention with restricted liberty of the inmates ordinarily providing sleeping accommodation and includes the hospital. .etc.

 Recreational Buildings:

A building in which people gathers for recreation, drama halls, cinemas, theatres, restaurants, places of worship, road, railways, and recreation places.

 Mercantile Buildings/ Commercial Building:

The Mercantile buildings are: for shops and multi-storied building and the display market building, providing goods, and provide service facilities, are considered mercantile building.

 Industrial Buildings:

These buildings are those used for manufacturing purposes.

 Types of Storage Buildings:

This group includes those buildings which are mainly used for the storage or sheltering of goods. The goods are highly combustible materials, vehicles, or animals. The buildings which come under this category are warehouses and cold storage. .etc.

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