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Principle of pile foundations
A pile foundation is necessary when the loads of a building will be higher than the upper soil layer can take. Piles are installed primarily to avoid settlements which could result in big damages and dangerous situations. In a limited number of projects piles are installed as ‘tension’ piles these are installed to prevent the object from lifting out of the ground. A well-known example are piles installed under the high tension electricity piles. Due to high forces created by wind the piles need to be ’anchored’ in the ground.
Soiltype versus Pile type
There are many different piles and piling methods. Some of the methods are very efficient in the weaker soils but can’t be executed in hard soils. In some cases for example when building a sky scraper it is necessary to install piles in to hard rock as well. The methods for this are rather limited.
To come to the best design of a pile foundation it is absolutely necessary to have a good report and investigation on the ground conditions where the jobsite will take place. A good report and inspection will minimize the risk of unexpected delay and additional costs. In Europe the system in which a cylinder is pushed into the ground to determine the soil type and friction is very popular in most parts of the world the so-called SPT (soil penetration report) is made. In this case little amounts of soil are excavated to determine the type of soil which can be encountered when installing piles. PVE does not supply soil investigation equipment but for the vibratory and impact hammers there are special prediction programs available which can help to determine the driveability of certain sheetpiles and casings in different ground conditions. Cone Penetration Test give a good soil report
Precast concrete piles (manufactured in a concrete factory) in most cases square but there are also countries where these piles are octagonal or round and even hollow. Steel tubes, H-beams with or without grout injection Cast in Situ pile driving. In this system a casing with temporary bottom plate is driven into the ground. When reaching the required level a reinforcement (steel cage consisting of some small bars) is lowered into the casing and fresh concrete is poured or pumped in the casing. After concreting the casing is extracted again to be used again in the same principle. Woltman is specialized in this field and has many different machines for this. Typical jobsite of the installation of precast concrete piles. The Woltman 50PR is a popular machine!