Current pile methodology and design improvements in engineering

Piles

The literature review for this particular study is conducted in order to ascertain what, if any, problems, solutions and circumstances are present with the manner in which current piles are developed, used and maintained. The literature should provide the researcher with data on the different aspects of current pile technology, as well as information on any new ideas or concepts that might be currently in the works regarding piles and pile technology.

Piles are considered a method for supporting structures in areas where loads are not normally supported. A good example of a pile would be a support structure that transfers load capacity from an inadequate area of support, to an area of adequate support such as in shallow waters or in areas where the soil might not be conducive to providing a good bearing support capacity. A recent report may have put it best when it espoused "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" (pg.1- pile foundation in engineering). This paper is specifically concerned with the best pile methodology currently in use. This study seeks to determine a more efficient, less costly manner for the use of piles, and in order to do so the current methodology must be thoroughly and efficiently examined. Current literature should provide the researcher with a clear understanding of exactly what, and how, piles are created, developed, built and maintained. After developing a comprehensive understanding of current pile technology, the researcher will then seek to determine an alternative method for building piles that yields a more effective and less costly method that can then be used to achieve the same, or an improved result.

A pile is built with the main purpose of providing support. A good pile support is based upon where the pile is situated regarding 'good bearing capacity'. This can be achieved in a number of ways. Finding good soil conditions into which a pile can be driven is the normal method for building a pile. However, there are times when good soil conditions are not available. In such times a pile may have to penetrate through the stratum of the poor bearing capacity soil to reach a good bearing capacity. When the tip of the pile "penetrates a small distance into a stratum of good bearing capacity, it is called a bearing pile" (p. 1 -- pile foundation in engineering). Another popular methodology is for the piles to be driven into limited soil conditions and develop a carrying capacity based upon the friction on the sides of the piles.

Pile Types

As Pile Foundation in Engineering reports "many times, the load-carrying capacity of piles results from a combination of point resistance and skin friction" (p. 1), when such an event takes place, the piles are called friction piles. There are other types of piles as well besides the friction and bearing piles. Some examples include the batter piles, vertical piles, compression piles and tension piles.

Batter pile and vertical piles are often used hand-in-hand as complementary tools. They are methods for transferring the load capacity from a pile to another structure such as a retaining wall or a sheet pile. The vertical pile, of course, is vertically situated under the structure and it is strengthened by a batter pile that is also situated under the structure but at an angle instead of vertically.

When this type of pile is employed, another horizontal pile can be used to transfer the weight bearing capacity to a sheet pile that is placed nearby in a vertical position near the structure. This type of pile can also be used beneath a retaining wall with the same transferring of capacity.

Another example of a common pile structure is the compression pile or tension pile. As the title states, a compression pile is compressed beneath a structure and is designed to alleviate the problems experienced by moving or swaying structures, such as during earthquakes or other profound events. A tension pile is also used with the same purpose in mind.

Most of the time, classifying the different types of piles is not set to a standard category. There are various manners in which the piles are classified including by material, by installation methods, and by how much ground is displaced when the piles are installed. For this study, classifying the piles will not be a high priority item, so as a general rule, the piles will be classified by the material which they are comprised of. On page 37 of the Pile Foundation in Engineering book, the following classification takes place which coincides with the pile categorization used by this study; 1) timber piles, 2) concrete piles, 3) steel piles, 4) composite piles, and 5) special type piles.

Currently, the two or three most common type of piles include timber, concrete or steel piles. As the Basics of Foundation Design states; "timber, because of its strength combined with lightness, durability and ease of cutting and handling, remained the only material used for piling until comparatively recent times" (p. 1). Recently, however, other materials such as steel and concrete have proven adaptable to the circumstances.

According to the text, both materials "could be fabricated into units that were capable of sustaining compressive, bending and tensile forces far beyond the capacity of a timber pile of like dimensions" (p. 1) and "concrete, in particular, was adaptable to in-situ forms of construction which facilitated the installation of piled foundations in drilled holes in situations where noise, vibration and ground heave had to be avoided" (p. 1). For this study then, a consideration that could be mightily discussed would include whether concrete was the most efficient and effective material for the new pile being developed, or whether some other material might be even more conducive to what is needed. Additionally, reinforced concrete was introduced some decades ago and has replaced (to a large extent) timber as a popular pile. The reasoning behind reinforced concrete is that it works well in dubious circumstances and "its durability was satisfactory for most soil and immersion conditions" (p. 2). The text also states that steel piles are becoming very commonplace, primarily due "to its ease of fabrication and handling and its ability to withstand hard driving" (p. 2).

Advantages and Disadvantages -- Piles

The advantages and disadvantages of the three most common type of piles (concrete, steel and timber) are numerous; since this study seeks to discover anything of importance concerning building a new, improved, longer lasting, less expensive and more durable pile, it is important to understand these advantages and disadvantages in order to develop a pile that addresses these issues.

Timber Piles

For example, according to the text, some of the disadvantages of using timber is that the pile can decay due "to fungi, insect attack, marine borer attack, and mechanical wear" (p. 39). Additionally, timber piles are "vulnerable to decay particularly when these are subjected to lowering and raising of the water table" (p. 40). It will be important for this study to determine what uses the pile being developed will be used for. Since timber is subject to decay when used in situations that introduce water, it might be better to stick with another type of material if the developed pile is going to be used there. Some of the advantages of the timber pile include the fact that when treated with creosote, oil-borne preservatives or salts the "life of timber piles above the permanent water tables can be considerably increased" (p. 39). If timbers are used under buildings or as foundation units they may also lose strength "under long-term effects of high temperatures" (p. 40) and "therefore, timber piles are not recommended under such structures" (p. 40).

A recent report on timbers states that "Wooden piles last a very long time underwater but are subject to decay when buried underground" (Columbia, 2011, p. 1). However, some of the problems that timbers face, especially when used for water-based scenarios can be overcome with coatings. According to the text, "problems of corrosion in marine structures have been overcome by the introduction of durable coatings and cathodic protection" (p. 40). Additional methods for protecting timber piles includes; placing fill around damaged piles, armor placement to provide resistance to abrasion, and concrete encasement of the piles. One recent report determined that a recently replaced timber bridge in Maryland was treated with not only creosote but as a dual protective scheme, "the timbers for the new bridge are pressure treated with copper naphthenate as well as being creosoted like the old bridge" (Zeyher, 2005, p. 23).

The project engineer determined that a dual protective approach made more sense than just the creosoting that took place in the past. Technology can certainly help in determining what amount of corrosion or debonding in taking place in timber piles as was recently displayed by a new evaluation methodology used on a West Virginia bridge supported by timber piles. According to the study "The results revealed that infrared thermography can be used as an effective nondestructive evaluation tool for detecting subsurface debonds in structural components wrapped with carbon or glass reinforced composite fabrics" (Halabe, Dutta, GangaRao, 2008, p. 1387). Perhaps, new technology can also assist the researcher during this study in determining exactly what type of pile to create.

Steel Piles

Steel piles are quite similar to concrete piles regarding the advantages and disadvantages. Additionally, steel piles offer a number of advantages that even concrete does not offer. For example; a steel pile can reduce driving costs and the H-section steel piles have a low displacement volume which can be a nice advantage when soil displacement or upheaval is a problem. Steel piles are known to be more expensive (for the most part) than are concrete piles, and steel piles also have the risk of corrosion that is not normally associated with concrete. In natural non-contaminated ground, the risk of corrosion still remains low.

Another advantage to the steel pile is that it can come in different forms such as; H-sections, tubular sections, box piles and sheet piles.

The different available forms allows the project engineer a certain amount of flexibility that might not be available with the concrete or timber piles. Installation of the steel pile is a much easier consideration as well, since steel piles can be driven at a much higher impact than timber. The bearing capacity of steel piles can also be increased with certain procedures not available with the other types of piles. If the steel pile is driven to a hard stratum, it can have an even higher carrying capacity and after it has been driven, it can be cut down to size or reshaped for further driving. A steel pile can also be extended quite easily, and if it happens to be too long can easily be cut down to size and the cut off portions can be used again or sold to recoup expenses.

Some of the disadvantages of steel piles are that they are subject to misalignment during the driving process. The idea during the driving process is to ensure that the steel pile is aligned in a proper fashion and there is currently no easy way in which to confirm that steel piles are aligned correctly so far under the surface. If the piles happen to be misaligned, then they really cannot be used as a support column with any degree of certainty. Other disadvantages are that a proper and valid soil test is usually required (an added expense), steel piles have a much smaller footprint than do concrete piles, and steel piles are normally more expensive than are concrete or timber piles.

Choosing Piles

On page two of the text a comparison of the different piles explains that oftentimes the choice of which pile to use in specific projects will most likely contain a consideration of what can be easily obtained in whatever country the project is taking place.

The text states that "timber piles are suitable for light to moderate loadings in countries where timber is easily obtainable and that steel or precast concrete-driven piles are not as economical as driven or bored and cast-in-place piles for land structures (p. 3). A number of other factors for choosing the different types of piles should also be considered with any project. Certainly one of the main factors is how the pile will be installed. As the text relates; "the method of installation of a pile may have profound effects on its behavior under load and, therefore its load carrying capacity" (p. 3).

A look at the pile installation methods will likely yield information of interest to the researcher who is seeking to develop a new and improved pile. Pile installation include a number methods such as; driven precast or driven cast-in-situ, bored cast-in-situ, jetting, jacking, spudding or screw methods. Quite often, the researcher is considering not only the effect of installation on the project's building or structure but on nearby buildings and structures as well. Installing piles can result in building or structure movements and vibrations that can result in structural damage to other buildings. Pile behavior is often based on what type of soil the pile is being driven into, and whether the pile will experience either static or dynamic resistance.

In Chapter one of Bengt H. Fellenius, Basics of Foundation Design, he states that "before a foundation design can be embarked on, the associated soil profile must be well established" (p. 1). Additionally, he states that "all foundation designs must start with determining the effective stress distribution of the soil around and below the foundation unit" (p. 1). Fellenius also states that the method of installation of a pile may have profound effects on its behavior under load, and therefore, its load carrying capacity (p. 3).

It is important then to take a look at the different installation techniques in order to determine how the newly developed pile is going to be installed in order to achieve lower expenses and an improved pile.

Page 11 of Pile Design and Construction Practice states that choosing a pile is based on three basic factors; 1) the location and type of structure, 2) the ground conditions, and 3) durability (Tomlinson, Woodward, p. 11). A brief synopsis of the specific pile that would work well based on each of these three factors is contained herein. First, the location and type of structure is a concern because each of the most common piles was developed to address each of the above listed factors. If the structure is one that will include a water-based approach then according to Tomlinson and Woodward; "a solid precast or prestressed concrete pile can be used in fairly shallow water, but in deep water a solid pile becomes too heavy to handle and either a steel tubular pile of tubular precast concrete pile is used" (p.12). Of course, timber piles can be used in shallow waters as well, with an excellent example being the Corpus Christi seawall built in 1939. The seawall consisted of approximately 2,000 tons of steel sheetpiling, 77,000 linear ft of timber piles, and 22,000 cu yd of concrete (Massengill, Moore, Garza, Hayes, 2008, p. 48). It is also an example of how even early project engineers were using a variety of piles and methods to create long-standing structures. The article states that the original purpose of the seawall was twofold: to protect the downtown area from storm surges and to stabilize and beautify the shoreline. However, the seawall was deteriorating and in the late 1990's an engineering firm was hired to assess the deterioration. What was discovered was that the timber piles were corroded (some severely) while the steel piles were relatively unscathed.

The article espoused the fact that "excavation work revealed voids in the fill material…up to 50% loss in the diameters of the timber piles, severe timber pile decay, and general honeycombing on the sides of the pile caps" (p. 48). Additionally the article states that the "dowels connecting the sidewalk to the seawall were severely corroded, sometimes to the point of nonexistence" (p. 48). One good point for the evaluation was that "the reinforcing steel in the sidewalks and seawall was in fair to good condition overall" (p. 48).

The steel piles were also evaluated, and what was discovered was that there was "various levels of deterioration, primarily in the form of surface corrosion, pits, and pitting holes in the steel sheet piles" (p. 49) and that the resulting corrosion "reduced the sheet pile's bending capacity by up to 36%" (p.49). It would be interesting to determine what effectiveness and corrosion levels were present when comparing the timber to the steel piles, especially in factoring in the costs of each. The question remains then as to how cost effective the timber piles were as compared to the steel piles?

When the seawall was reconstructed the engineering firm recommended the following; a new continuous steel sheet-pile wall option was recommended because it would provide both lateral stability and rear support for the seawall, supplementing the function of the deteriorating timber piles (p. 51).

It seemed as if, according to the article, that the timber piles had deteriorated more quickly than the steel piles, and that using a steel pile wall option to shore up the deteriorating timber piles was much more conducive and effective an option than replacing the timber piles.

As the Tomlinson and Woodward book states "timber piles are used for temporary works in fairly shallow waters" but that "large-diameter steel tubes are also an economical solution to the problem of dealing with impact forces from waves" (p. 12).

According to Tomlinson, using a pile for a structure on land is "open to a wide choice in any of the three categories (steel, timber, concrete). The least expensive piles are the bored and cast-in-place ones where "unlined or only partly lined holes can be drilled by rotary auger" (p. 12). Augered piles are also suitable when ground heave, noise and/or vibration is to be avoided. Tomlinson says that timber piles are suitable for light and moderate loads, while heavy and seismic loads would lean more towards the concrete or steel piles.

Determining the ground displacement and upheaval is a key component to determining what pile will be the most effective in specific cases. When developing a new pile, it will be necessary to determine where and when that pile will most likely find a niche. The developed pile is not being developed to replace any or all of the common piles now in use. Instead the new pile is being created to augment or complement the current offerings. Therefore, understanding what factors will play a role in where and when the new pile will be used, is most definitely important. According to Tomlinson, the ground conditions are the second factor that need to be considered in order to determine the correct pile to use. Tomlinson et al. states that "ground conditions, influences both the material forming the pile and the method of installation" (p. 12).

Without going into the dreary details of how to measure the composition of particular ground or conditions, Tomlinson et al. states that there are different types of piles that can be used based on whether the ground is stiff or contains hard fine-grained soils and rocks, or whether the ground provides hard driving conditions such as boulder clays or gravely soils. Piles that work well for penetrating heavier rocks are different than piles for lighter rocks. Of course, water-based piles throw the entire equation up in arms. One interesting note contained in this text was that "when piling in contaminated land using boring techniques, the disposal of arisings to licensed tips and measures to avoid the release of aerosols are factors limiting the type of pile which can be considered, and can add significantly to the costs" (p. 12).

Of course, the third factor could be the most important one of all, durability. Due to the significant cost of creating and installing piles, the length of time that the pile(s) will last is a definite consideration. Therefore, knowing that timber piles are cheap in some countries but that they are liable to decay above groundwater level, may be a deciding factor in whether to go ahead and pay the additional cost of using steel or concrete, even if such cost is significant. According to Tomlinson et al., steel piles can have a long life in ordinary soil conditions, if they are completely embedded in undisturbed soil, but the portions of the pile exposed to sea water or to disturbed soil must be protected against corrosion (p. 13).

Knowing all these factors and applying them to the creation of a new and improved pile is important to this study. Current literature is abundant on why certain piles work better than other piles in specific situations, but there is relatively little information on any new type of pile that could assist the researcher in this study.

Conclusion

There seems to be volumes of information on piles that have been around for decades, but very little information on any efforts to develop a new, more durable and less expensive pile. A recent study determined that "Piles composed of more than one material in their cross section have been used for more than 100 years" (Horvath, 2010, p. 875) so it could not be that others haven't thought about changing things. Obviously, early on, pile pioneers decided that timber was not the only way to go.

Of course, it could be that others have contemplated creating a pile that would work better than what is currently in use, and they could not come up with a better, or less expensive manner for doing so. It is hoped that this study, this research, may actually bear fruit in that regard. A new pile that is both longer lasting and less expensive could assist countries, states, cities and developers. One recent article extolled the virtues of a relatively new method of installation when concerned about the noise and vibrations associated with pile driving, especially when such actions create problems in urban areas and near sensitive buildings. What the article extolled was that "using drilled shafts instead eliminates the noise and vibration problems" (Landers, 2010, p. 22). Of course, a drilled shaft is not that new of an idea and it concerns installation, not a new type of pile, but at least there is some news on the pile front that lends credence to the concept that new ideas are being looked at.

Comparing what is currently being used; concrete, steel and timber, one would have to imagine that there is a better method for creating and installing piles. It is an objective of this study to determine what that method might be. Considering other components, other material, additional installation methods, better testing and even the natural resources available, means that there could be a way to accomplish the objective. If, by chance, the study ascertains the fact that there is no better method for creating or installing piles than the method(s) currently being used, then the study has accomplished its goal as well. If that is the case, then the study has determined that the best methods are already in use, which provides additional literature that supports the current methodologies.

Another study showed that there are other areas that can be addressed in new ways. The paper dealt with the "effects of using the new generation of reinforcements, Grid-Anchor for the purpose of reducing the permanent settlement of the foundations" (Boushehrian, Hataf, Ghahramani, 2009, p. 607). If there is a new generation of reinforcements, it also stands to reason that there can be a new generation of piles, installation techniques, or drilling processes that are stronger, more durable and less expensive than what is currently available.

It is hoped that this study will hope to discover those processes, or at the very least provide beneficial data for the pile and construction industry. This study seeks to determine a new type of pile, but would be satisfied to discover that what is currently being used, is the most efficient and effective manner for doing so.

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