Foundations and Pile Foundations in Engineering Construction

What Is Foundation?

All engineered construction work resting on the earth must be carried by some interfacing element called a foundation. The foundation is part of an engineered system that transmits to, and into, the underlying rock and soil the loads supported by the foundation and its self-weight.

The resulting soil stresses except at the ground surface are in addition to those presently existing in geological history and the earth mass from its self-weight.

The term superstructure(all structure) is commonly used to describe the engineered part of the system bringing Tthe load to the foundation, or substructure.

The term superstructure has particular significance for buildings and bridges; however, foundations also may carry only machinery, industrial support equipment (tanks, towers, pipes ), act as sign bases, & the like.

For it is better, for these reasons to describe a foundation the engineered system that interfaces the load-carrying components to the ground. It is evident based on this definition that a foundation is an essential part of the engineering system.

Type of Foundation, Use of Foundation, Application soil Conditions (Piling for Foundation)

What Is Pile Foundation?

The use of piles as a foundation can be traced since olden times. The art of driving piles was well-established in Roman times, and the details of such foundations were recorded by Vitruvius in 59 AD Today, pile foundation is much more common than any other types of deep foundation.

Modem pile driving started with the first steam pile drivers, invented by Nasmyth in 1845. Piles may be classified as follows:

Classification Based on Function

Based on the use or the function, piles may be classified as:

1. End bearing pile (See Figure a)
2. Friction pile (See Figure b)
3. Compaction pile (See Figure c)
4. Tension pile or uplift pile Anchor pile (See Figured)
5. Fender pile and dolphins (See Figure a)
6. Batter pile (See Figure f)
7. Sheet pile (See Figure g)

1. End Bearing Piles:

This type of piles is used to transfer load through water or soft soil to a suitable bearing stratum.

2. Friction Piles:

This type of piles is used to transfer loads to a depth of a friction load-carrying material using skin friction along the length of the piles.

Friction pile is a kind of pile foundation. This type of pile utilizes the frictional resistance force between the pile surface and adjacent soil to transfer the superstructure load.

Depending on the subsoil strata condition, resistance force due to friction can develop in a definite pile length of on the full length.

3. Compaction Piles:

Compaction is used to compact loose granular soil, thus increasing their bearing capacity. The compaction piles themselves don’t carry any load. Hence they may be of weaker material-sometimes of sand only.

Driven to compact the soil, the pile tube, is gradually taken out and sand is filled in its place, thus forming a ‘sandpile.’

4. Tension or Uplift Piles:

This type of piles anchor down the structures subjected to uplift due to hydrostatic pressure or due to overturning moment.

5. Anchor Piles:

This type of piles provides anchorage against horizontal pull from sheet piling or other pulling forces.

6. Fender Piles and Dolphins:

This type of piles is being used to protect waterfront structures against the impact of ships or other floating objects.

7. Sheet Piles:

These piles are commonly used as bulkheads, or as an impervious cutoff to reduce seepage and uplift under hydraulic structures.

8. Batter Piles:

This type of piles is used to resist large horizontal or inclined forces.

Classification of Piles Based on Materials

1. Concrete Piles:
   1. Precast
   2. Cast-in-situ
      1. Driven piles: Cased or uncased
      2. Bored piles: Pressure piles and under-reamed piles.
2. Timber Piles:
3. Steel Piles:
   1. H-piles.
   2. Pipe pile.
   3. Sheet pile.

Classification of Piles Based on Composition.

Composite Piles:

• 1. Concrete and timber.
  2. Steel and Concrete.

1. Precast Concrete Piles:

The precast concrete piles are commonly used for a maximum design load of near about 80 tonnes, except for large pre-stressed piles. They need to be reinforced to withstand handling stresses.

They require space for storage and casting, more time to set and cure before installation and heavy equipment for driving and manging. They also incur a high cost in cutting off the extra length or adding more distance.

2. Cast-In-Situ Piles:

The cast-in-situ piles are commonly used to get a maximum design load of 75 tonnes, except for compacted, pedestal piles.

They’re installed by pre-excavation, therefore eliminating vibration because of driving and the handling stresses.

3. Under-Reamed:

The under-reamed pile is a particular type of bored pile having an increased bulb or diameter at some point in this length, to anchor the expansive foundation soil subjected to alternate contraction

4. Timber Piles:

Timber piles have a small bearing capacity and aren’t permanent unless treated. They’re prone to damage from hard-driving, and shouldn’t be driven through hard stratum or boulders.

Composite piles are suitable which in the upper part of a pile is to project above the water table. This type of pile consists of a lower portion of untreated timber and an upper portion of concrete.

5. Steel Piles:

5.1. H-Piles:

Steel H piles (designated as HP) are suitable for penetrating rock as well as for driving through hard and resistant materials.

These piles displace a minimum of soil mass when driven through it and, therefore, can be easily driven through dense material without causing soil heave.

These piles can carry loads in the range of 80 kips (356 kN) to 240 kips (1068 kN) and have lengths in the range of 40ft (12m) to 100 ft (30m).

The maximum stresses in the pile section should not be more than 12,000 psi (82.7 M Pa) or as per the allowable code or specification for the job.

Steel H piles are generally driven through soft soils to hard-bearing strata. The classic case of danger for these piles driven through loose materials to hard, uneven rock is that these piles generally get demolished at their ends, resulting in questionable end-bearing capacity.

These piles should, therefore, be protected by attaching hard steel points at their ends.

Associated Pile Fitting Corp. (1985) cites a Federal Highway Administration Ohio test case where HP 10 x 42 piles were driven to hard limestone.

None of the piles that had APF cast steel points experienced damage despite hard-driving with up to 50,000 ft-lb hammer energy. In contrast, all piles driven without point protection got damaged even by driving energy of an 8700 ft-lb hammer.

5.2. Pie Piles:

Pipe piles have two main advantages: (l) the soil within the pipe can be easily taken out since there are no obstructions for cleaning out tools (e.g., no corners), and (2) the circular shape minimizes drag from waves and current forces in deep waters.

Pipe piles can also be inspected for any damage and/or deviation from plumb by lowering a light source within the hollow section. As shown in Figure 2.7, pipe piles can also be fitted with end caps in areas of hard-driving.

A typical type of pie foundation with tip fitting  

Where the hard-bearing strata are inclined or sloping, the flat plate at the end of the pipe may cause uneven stresses on the pipe pile resulting in stress concentration and crippling of the pile.

In such situations, conical points, as shown on the pile on the right in Figure 2.7, arc used to distribute the stress around the pipe.

Pipe piles are always filled with concrete after driving in the U.S.A. This gives the piles a higher section modulus and rigidity.

The pile’s arc generally economical in the range of 40 to 80 ft (12 to 24 m) and can carry loads as high as about 250 kips (1115 kN).

Pipe piles are most suited where the overburden is soft clays, silts, and loose-to-medium dense sand and is underlain by dense-bearing granular material. They also have successfully been installed in layered soils.

For example, Lee et al. (1984) describe a foundation system for the Shangri-La Hotel on the bank of Chao Phraya River in Bangkok, Thailand, which, among other facilities, also consists of a 27-story tower block.

The foundation soils consist of the soft Bangkok clay from the surface down to about 43 ft (13 m) underlain by alternating layers of stiff clay and sand.

Pumping of water from the sand layers has reduced piezometric head in the stiff clay and sand layers causing ground subsidence as much as 4 in./yr (10 cm (yr) in Bangkok.

Pile foundations designed to rest on dense sand layers will, therefore, be subjected to negative (downward) skin friction due to subsidence of surrounding clay layers that are undergoing consolidation.

The foundation system consisted of installing 24-in. (600 mm) diameter open-ended steel pipe piles. The installation procedure consisted of auger-pressing the pile through clay layers and through the near-surface sand layer.

Then the piles were driven with a K45 hammer with a drop height of about 8 ft (2.5 m) until a set of about 0.04 in. (1 mm) per blow was achieved. At this time, the piles were at about 180 ft (55 m) to 190 ft (58 m) depth below ground surface.

To reduce negative skin friction, some pipe pile sections that were to him in the settling clay layer depths were coated with a bitumen slip layer that was protected by a polyethylene layer.

Remaining pile lengths (sections) were left uncoated to mobilize the skin friction. These piles thus supported the imposed loads by mobilizing skin friction and end bearing in lower stiff clay and dense sand.

Pipe piles can be used as friction piles, end-bearing piles, and a combination of friction and end-bearing or even rock-socketed piles. They are also useful for marine structures where large diameter pipes can resist lateral forces in deep waters.

5.3. Any Other Type of Composite:

In the other type of composite piles, steel piles are attached to the lower end of the cast-in-place concrete pile. This type is used in a case where the required length of piles is greater than that available for the cast-in-place type.

Another type of steel piles that have been used to support light loads arc called screw piles. These piles consist of installing by screwing the helix steel sections down into the ground by applying the torque without digging into the ground.

The main advantage of this type of piles is that the structure or the equipment can be placed on the foundation immediately after the piles have been installed without having to return to the job site after the concrete has cured.

These piles can be installed in all soil types and have been used in several countries for mast and tower foundations.

As per the above figure gives examples of some typical application of these pile types that have been used in the past. These piles are mostly used to support lightly loaded foundations. All the above type of foundation (Piling Foundation Types).

Characteristics of Different Types of Foundation

In this section, the mechanisms of resistance of an individual foundation and a pile group are discussed. The function of different types of foundations is also addressed.

Complex loadings on top of a foundation from the bridge structures above can be simplified into forces and moments in the longitudinal, transverse, and vertical directions, respectively (As per below figure).

Resistances of an individual foundation 

Longitudinal and transverse loads are also called horizontal loads; longitudinal and transverse moments are called overturning moments; a moment about the vertical axis is called torsional moment.

The resistance provided by an individual foundation is categorized in the following (also see above figure).

1. End-bearing.Vertical compressive resistance at the base of a foundation; distributed end-bearing pressures can provide resistance to overturning moments;
2. Base shear. Horizontal resistance of friction and cohesion at the base of a foundation;
3. Side resistance Shear resistance from friction and cohesion along the side of a foundation;
4. Earth pressure: Mainly horizontal resistance from lateral Earth pressures perpendicular to the side of the foundation;
5. Self-weight Effective weight of the foundation.

Both base shear and lateral earth pressures provide lateral resistance of a foundation, and the contribution of lateral earth pressures decreases as the embedment of a pile increases.

For long piles, lateral earth pressures are the main source of lateral resistance. For short piles, base shear and end-bearing pressures can also contribute part of the lateral resistance. As per below table lists various types of resistance of an individual pile.

For a pile group, through the action of the pile cap, the coupled axial compressive and uplift resistance of individual piles provides the majority of the resistance to the overturning moment loading.

Horizontal (or lateral) resistance can at the same time provide torsional moment resistance.

The Resistance of an Individual Foundation 

A pile group is more efficient in resisting overturning and torsional moments than an individual foundation. As per the above table summarizes functions of a pile group in addition to those of individual piles.

Additional Foundation of Pile Group Foundations 

A pile group is more efficient in resisting overturning and torsional moments than an individual foundation. As per the above table summarizes functions of a pile group in addition to those of individual piles.

Frequently Asked Questions (FAQ)

What is a foundation in engineering construction?

A foundation is an interfacing element in construction that transmits loads from a structure to the underlying rock and soil. It supports the engineered system, ensuring stability and strength.

What are the types of foundations?

Foundations can be broadly categorized into two types:

• Shallow Foundations: Include spread footings, wall footings, combined footings, and mat foundations. They are used where the soil bearing capacity is adequate.
• Deep Foundations: Include pile foundations (floating and bearing), drilled piers, and caissons. They are used when the bearing capacity is found at greater depths.

What is a pile foundation?

A pile foundation is a type of deep foundation used to transfer loads to deeper, more stable soil layers or rock. Piles are long, slender columns made of materials like concrete, steel, or timber, driven into the ground to support structures.

How are piles classified based on function?

Piles can be classified based on their function as:

1. End Bearing Piles: Transfer load through water or soft soil to a bearing stratum.
2. Friction Piles: Transfer loads using skin friction along the pile’s length.
3. Compaction Piles: Used to compact loose granular soil.
4. Tension or Uplift Piles: Anchor structures subjected to uplift forces.
5. Anchor Piles: Provide anchorage against horizontal pulls.
6. Fender Piles and Dolphins: Protect structures from impacts.
7. Sheet Piles: Used as bulkheads or cutoffs to reduce seepage.
8. Batter Piles: Resist large horizontal or inclined forces.

What materials are used for piles?

Piles can be made from various materials, including:

1. Concrete: Precast or cast-in-situ.
2. Timber: Treated for durability.
3. Steel: H-piles, pipe piles, and sheet piles.
4. Composite: Combining materials like concrete and steel.

What are the characteristics of precast concrete piles?

Precast concrete piles are reinforced to withstand handling stresses, have a maximum design load of around 80 tonnes, and require heavy equipment for driving. They need curing time and space for storage before installation.

What are the advantages of pipe piles?

Pipe piles have advantages such as:

1. Easy removal of soil within the pipe.
2. Minimizing drag from waves and current forces.
3. Ability to inspect for damage and deviations.
4. Suitable for various soil conditions, including marine structures.

How do foundations resist various loads?

Foundations resist loads through mechanisms such as:

1. End Bearing: Vertical compressive resistance at the base.
2. Base Shear: Horizontal resistance from friction and cohesion.
3. Side Resistance: Shear resistance along the side.
4. Earth Pressure: Lateral resistance from earth pressures.
5. Self-weight: Effective weight of the foundation.

What is the difference between individual foundations and pile group foundations?

Individual foundations provide resistance to vertical and horizontal loads, while pile group foundations offer enhanced resistance to overturning and torsional moments due to the combined action of multiple piles and a pile cap.

Why are deep foundations like pile foundations preferred in certain conditions?

Deep foundations are preferred when the surface soil is not strong enough to support the load, and a more stable bearing stratum is located at greater depths. They provide the necessary support for heavy structures and in challenging soil conditions.