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.
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.
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…