Deep foundation

What is a deep foundation?

Deep foundations are construction methods in which the loads of a structure are transferred to deeper, load-bearing soil layers using foundation elements. This is particularly necessary if the layers close to the surface do not have the necessary load-bearing capacity or are susceptible to settlement. The use of deep foundations ensures the stability of structures even on problematic soils.

Deep foundation – possibilities

There are various methods of deep foundations, which are selected depending on the ground conditions, type of structure and economic aspects. The most common methods include

Pile foundation: With pile foundations, slender, rod-shaped elements, known as piles, are driven into the ground to transfer the loads of the structure to deeper, load-bearing layers. Piles can be driven, drilled or pressed into the ground. Pile foundations are particularly suitable for soils with a low load-bearing capacity in the upper layers.

Diaphragm wall foundation: Diaphragm walls are deep-reaching walls made of concrete or reinforced concrete that are installed in the ground and can be used both to secure the excavation pit and as a foundation element. They are constructed in a previously excavated slot, which is stabilized with supporting liquid until the concrete has been poured.

Well foundations: Well foundations consist of vertical, cylindrical shafts that are sunk down to the load-bearing layer and then filled with concrete. They are suitable for medium depths and are often used for bridge piers or masts.

Injection foundation: With injection foundations, a binding agent, usually a cement suspension, is injected into the ground under pressure to increase its load-bearing capacity. This method is often used to renovate existing foundations or to improve the properties of the subsoil.

Pile foundation as deep foundation

Pile foundations are one of the most frequently used methods of deep foundations and are characterized by their versatility and adaptability to different ground conditions. The various aspects of pile foundations are considered in detail below.

Types of piles: A distinction is made between different types of piles depending on the manufacturing process, material and load transfer:

In-situ concrete piles: These piles are produced directly on site by creating a borehole and then filling it with reinforcement and concrete. They are particularly suitable for heavy loads and can be adapted to the specific requirements of the subsoil.

Precast piles: Precast piles are prefabricated in factories and then driven into the ground on the construction site. This can be done by ramming, vibrating or pressing. They offer the advantage of high quality through controlled production, but require complex transportation and special installation equipment.

Steel piles: Steel piles consist of steel tubes or beams and are usually driven or vibrated into the ground. They are particularly resistant and are suitable for heavy loads and for use in difficult ground conditions.

Wooden piles: Historically, timber piles were frequently used, especially in areas with a lot of water. Today, they are mainly used for temporary constructions or in special cases. Their load-bearing capacity is limited and they are susceptible to biodegradation unless they are permanently submerged in water.

Load transfer for piles: With piles, the structural loads are transferred to the ground via two mechanisms:

Point pressure: The pile transfers the load directly to a deeper, load-bearing layer on which it rests with its point. This mechanism is particularly effective if there is a solid layer at an accessible depth.

Skin friction: The load is transferred to the surrounding soil by friction along the surface of the pile. This mechanism is particularly important in cohesive soils where there is no load-bearing layer at an adequate depth.

Dimensioning and planning the deep foundation

Planning a pile foundation requires a careful analysis of the subsoil and the expected loads. Important steps here are

• Subsoil investigation: Determination of the layer sequence, soil characteristics and groundwater conditions.

• Pile statics: Calculation of the required pile length, diameter and number of piles based on the loads and soil conditions.

• Selection of the pile system: Decision on a suitable pile type and the corresponding installation method.

• Proof of load-bearing capacity: Implementation

Pile breaking of bored piles

After the successful construction of a deep foundation (pile foundation), an indispensable step follows for the further processing and integration of the piles into the structure: pile head processing, also known as capping of bored piles.

Bored piles are usually produced with an excess length to ensure that they extend into the load-bearing soil layer and that no weak points arise due to soil mixing or uncontrolled settlement. Once the concrete has hardened, the upper, often contaminated or unevenly compacted areas must be removed to ensure a strong connection with the foundation or structure above.

Pile breaking is therefore a key task in specialist civil engineering that requires precise planning, specialized processes and the use of suitable machinery.

The Brextor^® method is an efficient, safe and qualitative method. With this method, not only individual piles, but also all types of pile walls (tangential, overlapped and broken up) are gently processed by machine. The work is done by one person and one machine. Weather conditions have no influence on performance here.