Pile Concrete: All you Need to Know

During construction, problems might arise concerning pile formation owing to several construction practices that may have been followed in the wrong way. It includes problems such as stagnant groundwater, deterioration in a permanent steel casing, geometric issues, an irregularity in concrete mix elements or measurements, and various other factors. 

The main problems that arise due to these construction faults in piles are the impact caused on the load bearing and distribution capacities which might cause the collapse of the whole structure. The transmission of top structure loads is carried out to a strong substrate with the help of friction while it is standing on bedrock. However, this very loud transmission is possible as long as no major integrity issues are present in the concrete piles.

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Different types of piles based on requirements

On the basis of their load transfer mechanism, piles can be categorised into the following types:

1. Friction piles: Friction piles are in charge of the resistance of loads through the development of frictional forces that are present along the pile surface. Therefore, the length and amount of resistance by the pile are equally proportional, which means a more extended length will ensure resistance to more load. The same is the case of the area.

An essential element that plays a significant role in increasing the amount of friction is the material that is being used for the pile, wherein a rougher surface will ensure a greater and better frictional resistance. Unlike bearing piles, friction piles do not require hard strata.

1. Bearing piles: These are piles that are supported on a hard stratum and are ground-driven in nature. Their function is to act like pillars and columns that help transfer vertical loads from the foundations to the deep strata underneath. These pillars also commissioned the resistance of load by bearing capacity, unlike friction piles.
2. Friction cum bearing piles: As the name suggests, these kinds of piles resist loads with the help of both action-bearing as well as frictional forces. These piles, therefore, are designed and created in order to function with the help of both of these resistive forces.
3. Guide piles: Guide piles refer to special kinds of piles that serve the function of stabilising any submerged construction in water by the formation of a cofferdam. 
4. Batter piles: These types of piles are programmed to resist seismic forces through their diagonal placement. The internal resistive force that may be developed due to both the bearing or friction components, together or separately, formed horizontally in the batter piles works to resist the horizontal external force.
5. Sheet piles: These kinds of piles are usually made out of steel and have interlocking edges that are driven into the soil in order to provide excavation support and soil retention.

On the basis of the material used, piles can be categorised as the following:

1. Composite piles
2. Timber piles
3. Steel piles
4. Concrete piles
5. Steel H or I-shaped piles

Types of pile formation methods

There are three methods of pile formation that are followed which are namely:

1. Direct slurry displacement method where the use of drilling fluid is prevalent during excavation to stabilise the borehole, after which the liquid detected is replaced with concrete with the help of a tremie pipe.
2. Dry method wherein the concrete is directly filled in after the excavation is conducted.
3. Casing method where the prevalence of temporary casing is taken into account as a form of support. 

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Types of problems that can occur during the formation or installation of piles

The following are the categories of problems that are further discussed in detail in the next section:

1. Problems that arise in the socketing or excavation of the foundation, such as the collapse of excavation, an excessive amount of groundwater, and shifting of neighbouring piles due to poor base formation.
2. Problems that arise in regard to concrete issues such as poor core strength of the concrete, inequalities in mixing elements, temperature fluctuations of the concrete being used, and mixing of bentonite into concrete in improper amounts or voids present on the concrete.
3. Problems that lie in the reinforcement and cage formations and the lack of the same.

Types of problems in detail

1. Due to the excavation continuing past the level of the groundwater table, it is necessary to regularly check the level of water in order to prevent seeping or the presence of excessive water in a pile. An effective way to prevent this problem is the use of bentonite, which, being higher in density, prevents the movement of the water. Steel casing is also an option to prevent this problem.
2. The concrete and steel halves present in a pile may be subject to damage if proper supervision is not carried out during the fabrication or construction process. Other than that, there might also be a presence of initial defects in them already. 
3. The steel casing is considered when the ground for construction seems weak, and bentonite seems inadequate for the strength that the piles need and may lead to problems. However, issues might arise in this case if the centre of the casing collapses during its placement or shifts due to the presence of soft soil as well as a lack of lateral stiffness. Casing in piling is always advised to be done under strict supervision because the failure to install casings may lead to a collapse of pile sides due to soft soil.
4. The presence of voids in the concrete can be found due to misplaced or improper compacting of concrete into piles, both with and without casing. Another factor leading to the formation or presence of voids in concrete is the withdrawal of casings if done.
5. In order to prevent displacement of piles’ location, the engineer in supervision must decide on the correct method or technique that can be used to solve lateral movement issues between adjacent piles.
6. Pile problems include a major issue that is named necking, which is observed while the process of casting the pile shaft is conducted in soft clay. This particular issue impacts the load-bearing capacity of the concrete piles and has been described as creating major problems like the formation of honeycomb-like structures of mud as well as improperly distanced concrete piles adjacent to the same. This also leads to the creation of new holes, wearing down the usability of the concrete altogether.

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What can be done to prevent such problems in piles?

1. Excessive water can be a commonly identified issue among pile problems, and Bentonite can be used for the prevention of the same. However, it is also important to regularly check the density of bentonite along with the volume of the water. After detailed observations, bentonite can be added or reduced as an adjustment in order to maintain a specific density of water.
2. To prevent problems with the steel casing process, careful supervision is advised during the casing installation, followed by inspection of work before concrete is placed. If in case, the problem occurs during the inspection, it is advisable to get rid of the casing and install a new one to prevent further problems. 
3. Making sure that the strength of the concrete being used is adequate should always be monitored. An insufficient amount of strength can be a result of a poor mix of concrete. Therefore, a proper mix measurement is required to be figured out along with consideration of adequate workability and quality control while the process of concreting to prevent future pile problems.
4. Pile problems can also arise in case of any kind of pile shape imperfection. This is said to fall under the bulging category, simply increasing the pile length and cross-section accordingly. Bulging is actually considered to increase the load capacity, but it is also placed under categories of pile problems and, therefore, must be investigated and prevented from being found.
5. To prevent pile problems, it is essential to supervise the type of casing being used, making sure that they are not only clean but also in proper shape and size and under good maintenance. The use of dirty casing might lead to issues like necking or creating a major issue when the casing is extracted at the required time. The formation of a bullet-shaped shaft base, which usually occurs due to improper cleaning of the base, must also be prevented in order not to impact the base-bearing capacity of the pile.
6. Continuous supervision must be there for the temperature of the concrete pile. The piles are required to be tested accordingly when the piling construction work begins, with the help of strain gauges in the first pile itself.

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