Deep foundation

The pile foundation is in the construction phase a variant of the deep foundation. With it, the loads of structures can be removed in deeper, more sustainable soil layers. Non- or poorly viable soil layers are bridged with piles. In the pile foundation piles (also called pilots) drilled into the ground or rammed until a sufficiently viable soil or rock layer is reached. The loads of the structure are then removed firstly by the friction of the pile with the ground ( skin friction ) and secondly on the peak pressure of the piles.

Taking into account both the structural behavior of the piles and the foundation plate in the initiation of structural loads into the ground, then is called a combined pile - raft foundation that.

• 2.3.1 Production

History

By the end of the 19th century ( and even today in smaller buildings such as boathouses ) sharpened wooden stakes or tree trunks were driven into the ground. Wooden poles are extremely strong and durable if they are permanently in the water. Wood piles in splash zones, eg at sites with changing groundwater levels, rot. As the largest pile foundation applies Venice, where the whole town was founded by centuries hundreds of thousands of tree trunks in the course. But also a lot of old and new buildings in the Netherlands, including the Royal Palace in Amsterdam and the old warehouses of the Speicherstadt in Hamburg, standing on wooden piles.

Today, partly (but not due to lack of strength in Germany ) stamped concrete columns, ie columns of plain concrete is used.

Various types of pile

Pile foundations can be prepared in various ways depending on the intended use, soil and environmental conditions consist of different materials, respectively.

• Purpose: For permanent structures reinforced concrete piles are particularly advantageous because of the material costs. Steel piles, however, can be re- drawn and re-used after use of the ground for temporary (auxiliary) structures.

• Soil conditions: Depending on how tight or loose the existing soil layers, it is possible to press piles, wash in, to screw or to ram. Regardless of the soil conditions, it is possible to make piles in predrilled holes or concreted into pre-drilled holes on site.

• Environmental Conditions: The appropriate installation method often depends on the environment and its development. For example, it is often not possible ramming piles installed in inner cities, because the vibrations are too large.

Steel piles

Steel piles in the form of tubes are referred to as full- displacement piles, since they displace the soil during installation to the side. If the steel pipe is not rammed, but turned around and pressed, one speaks of full displacement piles.

Steel piles in the form of double - T beams are often used as temporary piles, for example, temporary bridges and scaffolds. They can be grown again after use. Enough friction and the resultant between the flanges sheet for load transfer from these piles can be driven into the ground without further action. Does a higher load ( tensile forces ) are taken, such support may also be provided with Fußverstärkungen and pressed after ramming ( " Ramminjektionspfähle ", " RI - piles ").

In contrast to driven steel precast concrete piles is rammed steel piles are characterized by their breaking strength when they encounter obstacles such as large rocks. This makes it possible to ram steel piles themselves through hard soil layers up on the rock.

Are used rammed steel piles like in port construction and in the offshore area. Here are the resulting vibrations during installation not disturbing.

Ductile

The is a Ductile Precast Rammpfahlsystem made ​​of ductile cast iron. The pile is designed for allowable service loads of 300 kN to 1100 kN depending on the diameter and wall thickness of the pipe pile. The pile tubes are manufactured by centrifugal casting ductile iron. The centerpiece of the pile is the sleeve through which the pile can be made ​​endless and coupled to any length. At the lower end of the pile, the Pfahlfußplatte a distinction between two possible embodiments, the mörtelverfüllten pile and grouted pile. The mörtelverfüllte pile is equipped with a Pfahlfußplatte who enters the pile tube tightly. The pile is driven to the required final depth and then filled with concrete mortar. The load transfer occurs mainly through the peak pressure. Grouted pile when a base plate is used which is larger than the pile tube cross-section. This produces an annular space which is filled by the pressing. These mortar concrete is during pile driving sponsored by the pile pipe for pile base and pressed at the footplate into the ground and causes a concrete casing. The load transfer can then take place on the skin friction. The individual pipe sections are rammed with a quick blow hammer and special accessory as a carrier device is suitable, for example, a hydraulic excavator. This flexible pile system is applicable where large pile devices can not work even in cramped and rugged construction sites. Its versatile and economic feasibility in small construction sites, housing up to the construction site, to win this pile system in Germany is becoming increasingly important.

Precast concrete piles

Precast concrete piles of reinforced concrete or prestressed concrete are mainly used today worldwide with a square cross-section. The piles are used for a wide range of applications from simple halls to wind turbines. Precast concrete piles have two drawbacks. When they hit rock, they can break. In addition, the vibrations by ramming them in inner cities are so large that their use is not possible here.

Situ concrete piles

If the concrete placed on the spot ( now mostly ready-mix concrete ), one speaks of concrete piles. The diameter and the length of piles can be each adapted to the respective requirements.

In particular, the ultimate limit -situ concrete piles have to be distinguished in large and small bore ( " micro-piles "). Micropiles are smaller than 30 cm in diameter. From large-diameter piles one speaks accordingly in piles with a diameter greater than or equal to 30 cm.

An example of the use of concrete piles is the Warehouse A in Hamburg. The built in the sixties 108 times 85 -foot building, is in the soft Elbschlick and is founded on exactly 1111 reinforced concrete piles. Since the calculated weight of the memory that should be completely filled with cocoa sacks at times, was very large, the piles were designed for a load capacity of 160 tons and carried with a diameter of 50 cm. The reinforced concrete piles direct the weight by soil layers of clay and peat in stable sand layers.

Production

With a bored pile the earth is not displaced, but drilled a downwardly open steel pipe into the ground. The soil is thereby removed from the interior of the tube, then a steel reinforcement, or steel support member is introduced and filled in the tube with in situ concrete or mortar. According to the concreting the steel tube is pulled out gradually, while also possibly in depth standing or penetrating water is flushed from the heavier fresh concrete upwards until it is ultimately a " cushion" on the surface of the pile and the fresh concrete separates something there. This type Ortbetonpfahl is used for statically demanding ups like skyscrapers or bridges. Another use is in the juxtaposition of bored piles to create a continuous pile wall, which then serves as eg excavation safety.

Another method for producing bored piles, the Schneckenbohrtechnik. Here, a hollow continuous auger is "turned" into the ground. Once the desired depth is reached, concrete is forced through the hollow auger and it down so that the top. The steel reinforcement, after the auger and transported to the top floor was removed, vibrated into the still fresh concrete.

Wherein Pressbetonbohrpfahl Mörtelverpresspfahl or after manufacture, the spaces are pressed with mortar to provide additional support.

After the pile has been concreted and the concrete has set sufficiently, the pit will be excavated so that the pile heads emerge. The Bohrpfahlköpfe are then canceled to the required level, so that the pile head ends at the bottom of the foundation or the base plate. If the pile reinforced, binds to the reinforcement of the required length in said mating component a. Canceling the protruding pile head at first seems like a waste of materials. The reason for this " About concreting " of the piles is in the concreting. To avoid segregation of fresh concrete is cast with the tremie, ie the Betonierrohr always ends below the fresh concrete surface. The "bad", less viable concrete floats on top and has to be pried after setting.

Pile testing

The piles are subjected to different tests depending on the requirement. The tests must be performed by a certified auditor pile. The currently most common test method:

• Pile integrity testing
• Dynamic pile load tests
• Static pile load tests