Piles and pile foundations have been in use since prehistoric times. Pile is commonly described as a columnar element of a building foundation. Its function is to transfer the load from a superstructure to the hard layer in the soil, or on to the rocks.
The objective of this project is to identify piles and its uses in the construction industry, based on its types and suitability. This report is based on the three main types of piles, which are large displacement piles, small displacement piles and replacement piles.
Figure 1. Pile Construction
This report also contains research materials done by several authors have published various journals on the aforementioned topic, and numerous engineering books on pile, pile engineering, soil types, etc have been referred to assist this report. Many journals were consulted during the inception of this research. Topics like “Efficiency of Pile groups installed in cohensionless soil using artificial neural networks”, “Experimental study on pile-end post-grouting piles for super large bridge pile foundations”, etc were consulted. From these journals, it has been concluded an Artificial Intelligence application can be made to predict the efficiency of the pile. Based on the results, a pile cap can be created, or even grouting works can be performed to improve the load bearing of the structure.
The commonest function of piles is to transfer a load that cannot be adequately supported at shallow depths to a depth where adequate support becomes available, also against uplift forces which cause cracks and other damages on superstructure.
A bearing pile is described as a pile which can pass through weak material, whilst its tip get across a narrow distance, which in turn leads to a layer of improved bearing capacity. When piles are installed onto a layer with minimal ability to support, and the bearing capacity is being carried by friction which is acting on the sides of the pile, they are called friction piles.
Many times, the load-carrying capacity of piles results from a combination of point resistance and skin friction. The load taken by a single pile can be determined by a static load test. The allowable load is obtained by applying a factor of safety to the failure load.
Types of Piles
Piles are of various types. These piles are classified based on the scope of construction and soil type.
Figure 3. Common Driven Pile Types
Concrete Piles
Precast concrete piles can be either reinforced concrete piles or prestressed concrete piles.
Concrete is adaptable for a wide range of pile types. It can be used in precast form in driven piles, or as insertion units in bore piles. Dense well-compacted good- quality concrete can withstand fairly hard driving and it is resistant to attack by aggressive substances in the soil, or in seawater or ground water.
However, concrete is precast piles is liable to damage (possibly unseen) in hard driving conditions. Weak, honeycombed concrete in cast-in-situ piles is liable to disintegration when aggressive substances are precast in soils or in ground water.
Cast In Place Concrete Piles
Closed-ended hollow tubular sections of reinforced concrete or steel which are first driven into the ground and then filled with in-situ concrete.
Cast-in-place concrete piles with their shell driven with mandrel are typically 50 to 80 ft (15 to 24 m) long and can specifically be designed for a wide range of loads. Typical loads that these piles can carry are 50 to 120 kips (222 to 534 kN) provided the maximum stress in concrete, is not more than 33% of 28-day strength.
Figure 4. Cast-in-Situ Concrete Piles
The main disadvantages are that these piles are difficult to splice after concreting, their thin shells can be damaged during driving, and redriving is not recommended. Not the most economical solution, limited span length and requires formwork support. Generally, stress in steel should not exceed 0.35 x yield strength of steel.
Figure 5. Cast-in-Situ Concrete Piles
The advantages are tht they have low initial cost, and tapered sections can provide higher-bearing resistance in granular stratum. These piles are best suited as medium-load friction piles in granular soils. Absolute minimum depth, no deck joints and aesthetic for small stream crossings.
Precast Concrete Piles
Manufacturing of pre-cast concrete piles are done within the range of 250mm – 450mm. Mostly, the maximum section length can go up to 20m. There are various shapes of pile sections (eg. H-shaped, triangular-shaped, hexagonal-shaped, etc).
Figure 6. Precast Reinforced Concrete Pile
The construction of pre-cast concrete piles are done either in-situ or factory. Production and construction process widely affects the quality of the pile.
A pile shoe should be fixed to the pile, in case the soil deposits contain a lot of boulders. This protects the pile while performing “hard driving”.
For prestressed sections the maximum stresses should not exceed (0.33Æ’c – 0.27 pe); where pe = effective prestress stress on the section.
The main disadvantages of these piles are that they are difficult to handle without damage unless prestressed. They have a high initial cost, and prestressed piles are difficult to splice. It is also difficult to manufacture, subject to longitudinal and transverse cracking, not appropriate for curved or flared structures, complicated for skews.
The advantages of these pile types include high load capacities, corrosion resistance, and resistance to hard driving. Absolute minimum depth of precast bridge for short and intermediate spans. Expedites stage construction.
Drilled Shafts
Drilled shafts are also known as “caissons” or “piers” or “bored piles”. This is often known to be a cost effective solution which is practiced worldwide. This is a widely used type of deep-foundation. Drilled Shafts are widely used in the construction of bridges and large buildings. This technique is used in construction areas where large loads along with lateral resistance are key factors.
Figure 7.1. Drilled Shaft
The main advantages are that it is economical, it could minimize pile need for pile cap, slightly less noise and reduced vibrations, adapts easily to varying site conditions and has high axial and lateral loading capacity.
The main disadvantages are that it is extremely sensitive to construction procedures, not ideal for contaminated sites, and lack of qualified inspectors.
Figure 7.2. Drilled Shaft
A Drilled Pile is made of concrete or grout and cast or poured, in a plastic state, into a drilled hole in the earth. Augercast, Drilled Shafts, Drilled Cast-in-situ and, their variations are all forms of drilled piles. Completed drilled piles cannot be easily inspected after installation and can be difficult to install in very soft or loose soils, wet, and marine conditions.
A Drilled Pile removes soil from the ground and the resulting round hole is filled with concrete or grout.
Steel Piles
These are more expensive then timber or concrete but this disadvantage may be outweighed by the ease of handling of steel piles, by their ability to withstand hard driving, by their resilience and strength in bending, and their capability to carry heavy loads. Steel piles can be driven in very long lengths and cause little ground displacement. They are liable to corrosion above the soil line and in disturbed ground, and they require cathodic protection of a tong life is desired in marine structures. Long steel piles of slender section may suffer damage by buckling if they deviate from their true alignment during driving.
Figure 8. Steel Piles
Steel piles are strong, lightweight to handle, and capable ofcarrying heavy loads
to deeper bearing stratum. They can be extended to any length since splicing is
relatively easy, and these can also be readily cut to any required length. This makes steel piles suitable for areas where the depth of bearing strata are variable. Various types of steel piles in common use include pipe piles, H-section piles, box section piles, and tapered and fluted tubes. Pipe piles and H-section piles are the most commonly used steel piles in engineering practice. Steel pipe piles can either be driven open ended or closed ended. Open-ended piles will experience less driving resistance and can be drilled through obstructions such as boulders and bedrock.
The piles are 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 overburden is soft clays, silts, and loose-to-medium dense sand and is underlain by dense-bearing granular material.
H-Piles
A form of Steel pile is known as “H-Pile”. These are wide-flanged sections made of steel. The biggest advantage of this pile is that the displacement of soil becomes very less, when compared against other soil displacement methods practiced in the world. The H-pile falls under ‘small displacement’ category.
Figure 9. H-Piles
Timber piles cannot be driven through hard ground.
Steel H-piles are essentially end-bearing piles. Due to limited perimeter area, H-piles cannot generate much frictional resistance.
Corrosion is a major problem for steel H-piles. The corrosion is controlled by adding copper into steel.
H-piles are easily spliced. They are ideal for highly variable soil conditions.
H-piles can bend under very hard ground conditions. This is known as dog legging, and the pile installation supervisor needs to make sure that the piles are not out of plumb.
H-piles can get plugged during the driving process.
If the H-pile is plugged, end bearing may increase due to larger area. On the other hand, skin frictionmay become smaller due to smaller wall area.
When H-piles are driven, both analyses should be done (unplugged
and plugged) and the lower value should be used for design.
Unplugged: Low end bearing, high skin friction.
Plugged: Low skin friction, high end bearing.
Advantages are that H-pile is available in various lengths and sizes easy to splice high capacity low soil displacement many penetrate larger obstructions with driving shoes.
The disadvantages are that it is vulnerable to corrosion, hence not recommended as friction piles in granular soils may force the h-pile to bend on the weaker axis, during the “pile-driving” process. Due to this, there is a high chance of curvature, which may result when the piles are driven into a larger depth.
Cylindrical
Cylindrical piles have a high axial compressive strength for high bearing capacities; they have high moments of inertia and therefore can serve well as both a column and a foundation pile under high vertical and lateral loads.
Figure 10. Cylinder Piles
Cylinder piles are often used in nearshore applications where smaller foundation piles would require cofferdam construction and other costly measures. Drilled shafts have similar load bearing properties and capabilities, however, they are generally more costly than piles installed by impact driving.
Timber Piles
Untreated timber piles may be used for temporary construction, revetments, fenders and similar work; and in permanent construction where the cutoff elevation of the pile is below the permanent ground water table and where the piles are not exposed to marine borers. They are also sometimes used for trestle construction, although treated piles are preferred. Timber piles are difficult to extend, hard to anchor into the footing to resist uplift, and subject to damage if not driven carefully. Timber piles also have a maximum allowable bearing capacity of 45 Tons, whereas most structure piles are designed for at least 70 Tons. These piles are mostly installed by driving and are best suited as friction piles in granular material.
Figure 11. Timber Piles
The main advantages of timber piles are that they have low initial cost, are easy to handle, and resist decay when they are permanently submerged.
The main disadvantages are that it is tough to splice, are vulnerable to damage in hard driving, and are susceptible to decay unless treated. Treatment becomes necessary when these piles are intermittently submerged.
Composite Piles
Materials may be used in combination in piles and the most common example is the use of steel and concrete. This may be by using driven steel casings of various types filled with a structural core of concrete, or a steel pile protected externally by concrete casing; the latter is normally only possible for exposed lengths of piles such as would be encountered in a jetty structure. There are, however, forms of steel pile, which have grout pipes throughout their length, which are used for forming a protective outer casing after driving.
Figure 12. Composite Piles
The maximum stresses in timber, steel and concrete should not exceed the values specified above for various materials.
The main disadvantage of these piles is that it is difficult to attain good joint between two materials.
The main advantage is that considerable length can be provided at comparatively low cost. High capacity may be possible depending on materials.
use of piles in construction
There are two types of piles used for construction:
Displacement Piles
Non-Displacement Piles
DisplacemeNt Pile
The type of pile, which is rammed into the ground, which does not remove the soil, but displaces the soil downwards and sidewise. This type of pile foundation is called displacement pile.
Figure 13. Displacement Piles
This method piles displace soil during their installation, such as driving, jacking, or vibration, into the ground. Examples of these types of piles are timber, precast concrete, prestressed concrete, close-ended steel pipe, and fluted and tapered steel tube piles.
The advantages of displacement piles are:
Material forming pile can be inspected for quality.
Soundness before driving.
Not liable to squeezing or necking.
Construction operation not affected by ground water.
Projection above ground level advantageous to marine structures.
Can be driven in the very long lengths.
The disadvantages of displacement piles are:
May break during driving, necessitation replacement pile.
Unseen damages may occurring thus decreasing the carrying capacity.
Noise pollution may be caused during hammering.
Vibration caused during the hammering process may pose a threat to nearby structures.
Non-DisplacemeNt Pile
These Piles do not displace soil during their installation. These piles are formed by first removing the soil by boring and then placing prefabricated or cast-in-place pile into the hole from which an equal volume of soil was removed. Their placement causes little or no change in lateral ground stress, and, consequently, such piles develop less shaft friction than displacement piles of the same size and shape. Piling operation is done by such methods, as augering (drilling, rotary boring) or by grabbing (percussion boring). Most common types of no displacement piles are bored and cast-in-place concrete piles.
The advantages of non displacement piles are:
Material forming pile is not governed by handling or driving stresses.
Can be installed in very long lengths.
No ground heaves.
Can be installed in conditions of low headroom.
Figure 14. Non Displacement Piles
The disadvantages of non displacement piles are:
Concreting in water-bearing soils require special techniques.
Inspection of concrete cannot be done after installation.
Cannot be extended above ground level without special adoption.
LITERATURE REVIEW
Description of Journals
This section contains the description paragraph for the 5 technical journals which has been chosen to support the main topic of research.
Adel M. Hanna, George Morcous, and Mary Helmy (2004) Efficiency of Pile Groups Installed in Cohensionless Soil Using Artificial Neural Networks.
Adel M.Hanna, George Morcous and Mary Helmy evaluated the efficiency of pile groups installed in cohension-less soil subjected to axial loading. The authors feel that a resistance to the column load may result in a major difference between the total capacity of the individual piles and the group piles. This could lead to destruction of the building. The authors have developed an ANN (Artificial Neural Network) model to assist the research. They have found that the ANN model is nearly 80% accurate to the predicted value. The predictions are very accurate, even with low tolerance values. They have also made an ANN model which can be easily updated when new data are obtained from laboratory and field tests.
Kevin J.Bentley and M.Hesham El Naggar (2000). Numerical Analysis of Kinematic Response of Single Piles
Kevin and Hesham have done a research on single piles, after anticipating the catastrophic losses in terms of human life and economic assets due to the earthquakes. They wanted to develop a model which evaluates the effects of ground motion on piles. Their aim was to develop a finite element model that can accurately model the kinematic soil-structure interaction of piles, accounting for non linear behavior of soil, discontinuity at the pile soil interface, energy dissipation and wave propagation. They found that the effect of the response of piles in elastic soil was slightly amplified in terms of accelerations and Fourier amplitudes.
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The authors have taken a good amount of information from previous researches made. They have found that the previous studies had its own drawbacks, which were concluded that interaction effects on kinematic loading are not significant at low frequencies but are significant for pile head loading. The authors used finite element program, ANSYS to analyze the full 3D transient method. They have found that the deflections obtained in the study were slightly greater than those from other tests. The authors concluded that the effect of soil layer overlaying the bedrock was to amplify the bedrock motion, which results in a higher free-field motion for the soil parameters used in the analysis. Increased Fourier amplitudes at the predominant frequency was an effect of soil plasticity. It slightly decreased the maximum acceleration amplitudes.
Jinoh Won and Fred H. Kulhawy (2009) Reduction of Pile Head Displacement for Restrained Head Single Pile.
The authors conducted a study on the effect of pile head fixity on the displacement of laterally loaded pile groups using analytical methods. It was found that the soil parameters have a major influence on the reduction factor, while the pile property influence is relatively minor. The rationale behind the problem is described as most pile foundations have pile cap that reduces the lateral displacement because of restraining effect on the pile heads. The authors learned that the previous researches which were done were for small-scale tests only. The authors have performed numerous tests, from which they found that there is a variation of reduction factor with soil properties for the drained cohensionless model. The authors have done a quantitative analysis to investigate the effect of pile head restraint on the displacement using an analytical method. Their design chart is matched reasonably well with the experimental and numerical data.
Ling-gang Kong and Li-min Zhang (2007). Effect of Pile-cap Connection on Behaviour of Torsionally Loaded Pile Groups
Evaluation of the responses, under torsion, of fixed as well as pinned pile cap was done by the authors. They have researched that, the torsional capacity of the pile group is significantly influenced by the pile-cap. The same applies with the pile-group’s torque assignment. The authors claim that grouped piles are usually used as foundations for offshore platform, bridge bents and tall buildings. Due to natural disturbances like wind and wave actions, ship impacts or high-speed vehicles, the grouped piles may be exposed to significant torsional loads, leading to destruction and catastrophic effects on them. The authors have found that the lateral ad torsional resistance of the individual piles is mobilized by a pile group which is subjected to torsion. This could thrust up to 50% of the applied force, whilst the pile-cap foundation is fixed. From the research it has been noted that under loose sand the pile bend a minimal degree. Whereas under dense sand, and the same load, the pile bend less than the loose sand. They have modeled nonlinear soil response and major pile-soil-pile interactions and coupling effect in a pile group.
Weiming Gong, Guoliang Dai and Haowen Zhang (2009) Experimental Study on pile-end post-grouting piles for super-large bridge pile foundations.
The authors made an experimental study on pile-end and post-grouting piles for very large bridge-pile foundations. Before the after-grouting works were evaluated, the authors wanted to analyze the bearing capacity, bearing characteristics and displacement. The authors introduced 21 test piles to perform the experiment. The technique was implemented to increase the capacity as well as decrease settlement. The author has done a lot of background researches, across various bridges. From the research it has been found that the capacities are greatly enhanced after pile-base grouting. The Q-s curve before grouting decrease sharply under small loads and have great deviations from existed geological values, which attributes to long term interval between drilling and grouting. So the authors have proved that, by grouting, they have steadily increase the bearing capacity of a bridge.
Order of Paragraphs
Kevin and Hesham have done a research on single piles, after anticipating the catastrophic losses in terms of human life and economic assets due to the earthquakes. They wanted to develop a model which evaluates the effects of ground motion on piles. Their aim was to develop a finite element model that can accurately model the kinematic soil-structure interaction of piles, accounting for non linear behavior of soil, discontinuity at the pile soil interface, energy dissipation and wave propagation. They found that the effect of the response of piles in elastic soil was slightly amplified in terms of accelerations and Fourier amplitudes.
The authors have taken a good amount of information from previous researches made. They have found that the previous studies had its own drawbacks, which were concluded that interaction effects on kinematic loading are not significant at low frequencies but are significant for pile head loading. The authors used finite element program, ANSYS to analyze the full 3D transient method. They have found that the deflections obtained in the study were slightly greater than those from other tests. The authors concluded that the effect of soil layer overlaying the bedrock was to amplify the bedrock motion, which results in a higher free-field motion for the soil parameters used in the analysis. Increased Fourier amplitudes at the predominant frequency was an effect of soil plasticity. It slightly decreased the maximum acceleration amplitudes.
The authors conducted a study on the effect of pile head fixity on the displacement of laterally loaded pile groups using analytical methods. It was found that the soil parameters have a major influence on the reduction factor, while the pile property influence is relatively minor. The rationale behind the problem is described as most pile foundations have pile cap that reduces the lateral displacement because of restraining effect on the pile heads. The authors learned that the previous researches which were done were for small-scale tests only. The authors have performed numerous tests, from which they found that there is a variation of reduction factor with soil properties for the drained cohensionless model. The authors have done a quantitative analysis to investigate the effect of pile head restraint on the displacement using an analytical method. Their design chart is matched reasonably well with the experimental and numerical data.
The authors carefully studied the reaction of two types of pile cap (fixed & pinned) under torsion. They have researched that, the torsional capacity of the pile group is significantly influenced by the pile-cap. The same applies with the pile-group’s torque assignment. The authors claim that grouped piles are usually used as foundations for offshore platform, bridge bents and tall buildings. Due to natural disturbances like wind and wave actions, ship impacts or high-speed vehicles, the grouped piles may be exposed to significant torsional loads, leading to destruction and catastrophic effects on them. The authors have found that the lateral ad torsional resistance of the individual piles is mobilized by a pile group which is subjected to torsion. This could thrust up to 50% of the applied force, whilst the pile-cap foundation is fixed. From the research it has been noted that under loose sand the pile bend a minimal degree. Where as under dense sand, and the same load, the pile bend less than the loose sand. They have modeled nonlinear soil response and major pile-soil-pile interactions and coupling effect in a pile group.
Adel M.Hanna, George Morcous and Mary Helmy evaluated the efficiency of pile groups installed in cohension-less soil subjected to axial loading. The authors feel that a resistance to the column load may result in a major difference between the total capacity of the individual piles and the group piles. This could lead to destruction of the building. The authors have developed an ANN (Artificial Neural Network) model to assist the research. They have found that the ANN model is nearly 80% accurate to the predicted value. The predictions are very accurate, even with low tolerance values. They have also made an ANN model which can be easily updated when new data are obtained from laboratory and field tests.
The authors made an experimental study on pile-end and post-grouting piles for very large bridge-pile foundations. Before the after-grouting works were evaluated, the authors wanted to analyze the bearing capacity, bearing characteristics and displacement. The authors introduced 21 test piles to perform the experiment. The technique was implemented to increase the capacity as well as decrease settlement. The author has done a lot of background researches, across various bridges. From the research it has been found that the capacities are greatly enhanced after pile-base grouting. The Q-s curve before grouting decrease sharply under small loads and have great deviations from existed geological values, which attributes to long term interval between drilling and grouting. So the authors have proved that, by grouting, they have steadily increase the bearing capacity of a bridge.
Addition of Introductory and Concluding Sentences
Pile is commonly described as a columnar element of a building foundation. Its function is to transfer the load from a superstructure to the hard layer in the soil, or on to the rocks. Kevin and Hesham have done a research on single piles, after anticipating the catastrophic losses in terms of human life and economic assets due to the earthquakes. They wanted to develop a model which evaluates the effects of ground motion on piles. Their aim was to develop a finite element model that can accurately model the kinematic soil-structure interaction of piles, accounting for non linear behavior of soil, discontinuity at the pile soil interface, energy dissipation and wave propagation. They found that the effect of the response of piles in elastic soil was slightly amplified in terms of accelerations and Fourier amplitudes.
The authors have taken a good amount of information from previous researches made. They have found that the previous studies had its own drawbacks, which were concluded that interaction effects on kinematic loading are not significant at low frequencies but are significant for pile head loading. The authors used finite element program, ANSYS to analyze the full 3D transient method. They have found that the deflections obtained in the study were slightly greater than those from other tests. The authors concluded that the effect of soil layer overlaying the bedrock was to amplify the bedrock motion, which results in a higher free-field motion for the soil parameters used in the analysis. Increased Fourier amplitudes at the predominant frequency was an effect of soil plasticity. It slightly decreased the maximum acceleration amplitudes.
The type of soil is an important entity while fixing piles. The authors conducted a study on the effect of pile head fixity on the displacement of laterally loaded pile groups using analytical methods. It was found that the soil parameters have a major influence on the reduction factor, while the pile property influence is relatively minor. The rationale behind the problem is described as most pile foundations have pile cap that reduces the lateral displacement because of restraining effect on the pile heads. The authors learned that the previous researches which were done were for small-scale tests only.The authors have performed numerous tests, from which they found that there is a variation of reduction factor with soil properties for the drained cohensionless model. The authors have done a quantitative analysis to investigate the effect of pile head restraint on the displacement using an analytical method. Their design chart is matched reasonably well with the experimental and numerical data. The frictional resistance of the pile is directly proportional to the soil cohesiveness, which means if the soil is cohesive, it will have a better contact with the area of the side pile.
The pile cap distributes the load from the pillars, or piers, to the piles. The authors studied the reaction of the two pile caps (fixed and pinned) cap under torsion. They have researched that, the torsional capacity of the pile group is significantly influenced by the pile-cap. The same applies with the pile-group’s torque assignment. The authors claim that grouped piles are usually used as foundations for offshore platform, bridge bents and tall buildings. Due to natural disturbances like wind and wave actions, ship impacts or high-speed vehicles, the grouped piles may be exposed to significant torsional loads, leading to destruction and catastrophic effects on them. The authors have found that a pile group subjected to torsion simultaneously mobilizes lateral and torsional resistance of the individual piles and the torsional resistance could thrust up to 50% of the applied force, whilst the pile-cap foundation is fixed. From the research it has been noted that under loose sand the pile bend a minimal degree. Where as under dense sand, and the same load, the pile bend less than the loose sand. They have modeled nonlinear soil response and major pile-soil-pile interactions and coupling effect in a pile group.
An Artificial Intelligence based application need to be created which would perform tests based on experimental values. Adel M.Hanna, George Morcous and Mary Helmy evaluated the efficiency of pile groups installed in cohension-less soil subjected to axial loading. The authors feel that a resistance to the column load may result in a major difference between the total capacity of the individual
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