Introduction

Concrete Piles are commonly used as foundation systems in many countries over the world. The main function of load bearing piles is to transfer the load to lower levels of the ground which are capable of sustaining the load with an adequate factor of safety and without settling at the work load by an amount detrimental to the structure that they support. Pile foundations are considered when: structural loads need to be transmitted through soils exhibiting low bearing capacity to deeper more competent strata, to resist uplift of lateral forces, to support structures over water and carry loads below scour depths , and/or building in areas where future adjacent excavations are expected.

The load carrying capacity of a pile is a function of its structural strength and integrity: the strength and deformation properties of the foundation soils and the pile-soil interaction characteristics. Piles derive their carrying capacity from a combination of friction between the soil and the surface of the pile, and end bearing at the point or base. The former (friction piles) is likely for piles in clay and silts and where long pockets are formed in soft rock. The latter (end bearing) applies to piles settling in deeper strata where soil conditions are harder such as compact gravel, hard clay or bedrock.

A concrete pile can be used for other structural applications beyond a deep foundation. Piles are used to reinforce walls, in which case they may be temporary or permanent. They are also used to reinforce levees and other structures which might be at risk of collapse.

Piles come in a range of sizes. An engineer can determine what kind of concrete pile is most appropriate for a project, and can monitor the placement of the pile to confirm that it is not compromised, and to check to see that it will be able to withstand a support load. Engineers use a variety of techniques to monitor and test piles both before they are delivered and after they are installed to confirm that they are safe before proceeding to the next step of construction.

Why Precast Concrete Piles?

As cities expand, land with poor soil conditions are encroached to build residential and commercial property to meet and sustain expanding economies and population that comes with such growth. Areas with poor soil conditions call for the need of deep foundations as some types of ground cannot support a building safely, and a deep foundation may be used to anchor a building to bedrock. The piles distribute the weight of the finished structure safely, reducing the risk of structural failure or collapse.

The usage of precast concrete piles to tackle deep foundation is an excellent solution. Precast concrete piles are versatile as they can be used in any soil conditions. Readily-engineered cross-sections can be chosen to accommodate and suit design criteria budget constrains. Concrete is durable, and requires no toxic preservatives in order to prevent its deterioration. With the usage of high strength concrete, precast concrete piles have high resistant to chemical damage in corrosive soil compared to steel bearing piles and timber piles.

Precast piles provide maximum structural efficiency with the utilization of high strength concrete, yet at the same time requiring relative low material consumption. In addition, the energy consumption of concrete is extremely low, compared to other construction materials. Prefabrication of concrete piles allows for quicker completion schedules as foundation work can begin without the need for time consuming preparation required in cast in-situ piles. Modes of structural deficiencies in cast in-situ piles include separation of concrete, necking, voids, or contamination of concrete with soil which. These problems can cause uncertainty regarding the shape and structural condition of cast in-situ can be reduced by using precast concrete piles.

Alternatively, Timber piles require rigorous selection procedure as different types of softwood and hardwood have different attributes which make them unique, and only suitable for specific foundation work. Moreover, the choice will depend upon availability in suitable sizes, the expected useful life and the relative cost, including preservative treatment which can be environmentally hazardous. Availability in the required lengths is a limiting factor. On the other hand, steel bearing piles cannot be used in corrosive soil as it will cause the steel to corrode and compromise its integrity. Moreover, steel is expensive.

Pile Driving Methods

Hydraulic Jack-In

This method utilises static force to install piles. The force for pile installation is exerted from hydraulic jacks that attain their reaction from counter weights placed on the piling frame with a safe working load of 13 ton to 50 ton. The total weight of the piling frame and counter weights is in excess of twice the working load of the desired pile so that all piles can be jacked to set with a factor-of-safety of two.

Hydraulic hammer

A hydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving piles.Hydraulic hammers are more environmentally acceptable than the older, less efficient hammers as they generate less noise and pollutants. However, in many cases the dominant noise is caused by the impact of the hammer on the pile, or the impacts between components of the hammer, so that the resulting noise level can be very similar to diesel hammers.

Diesel hammer

A modern diesel pile hammer is a very large two-stroke diesel engine. The weight is the piston, and the apparatus which connects to the top of the pile is the cylinder. Pile driving is started by having the weight raised by auxiliary means — usually a cable from the crane holding the pile driver — which draws air into the cylinder. The weight is dropped, using a quick-release. The weight of the piston compresses the air, heating it to the ignition point of diesel fuel. Diesel fuel is added/injected into the cylinder. The mixture ignites, transferring the energy of the falling weight to the pile head, and driving the weight back up. The rising weight draws in fresh air, and the cycle starts over until the fuel runs out or is stopped by the pile crew.

Figure 1 (L-R): Examples of piling machinery ;Mobile Hydraulic press-in, Hydraulic press-in , and Hydraulic Hammer.

 

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