Piled Raft Foundations Blog

Raft foundations are popular for construction projects, as they offer a stable and reliable solution for buildings on challenging or unstable ground conditions. The foundation is typically constructed in a multi-layered approach, starting with a compacted hardcore base, approximately 100mm thick, which provides a solid and even foundation for the subsequent layers.

Next, a layer of binding concrete, around 50mm in depth, is carefully laid atop the hardcore base. This concrete layer serves as a bonding agent, forming the raft itself seamlessly on top. The raft, the main structural element of the foundation, is typically reinforced with steel to prevent cracking and ensure its long-term integrity.

Strategic thickened areas or stiffening beams are incorporated into the design to enhance the raft's strength and stability further. These beams, which can be positioned above, below, or within the depth of the raft, provide extra support for specific load-bearing areas, such as under internal walls or columns. This tailored approach ensures the foundation can effectively distribute the building's weight across the slab and evenly into the ground.

In cases where the ground conditions are particularly poor, the thickness of the raft might need to be increased to accommodate the additional load-bearing requirements. However, before determining the optimal raft design, the engineer conducts a thorough site assessment to evaluate the ground's condition and determine the most suitable foundation solution.

In instances where the ground conditions are deemed unfit for a traditional raft foundation, alternative solutions, such as piling, may be necessary to ensure the structural integrity and safety of the building. The raft design also features an 'edge beam,' a reinforced steel cage that is carefully assembled on-site to provide additional support and stability along the perimeter of the foundation.

By incorporating these design elements, raft foundations can adapt to various site conditions, offering a robust and reliable solution for various construction projects.

Constructing a solid foundation is crucial for structural integrity and longevity. The concrete toe often supports the external leaf of the wall, providing a sturdy base. On the other hand, the raft design typically requires a well-prepared sub-base to ensure a level ground. This sub-base is typically made of a compacted layer of hardy, granular material, such as crushed stone or gravel, known as hardcore. This sub-base must be meticulously compacted manually or with specialized machinery to create a stable and unyielding foundation.

The steel reinforcement used within the concrete raft is critical, as it enhances the structure's overall strength and resilience. It is crucial that the steel reinforcement, whether in the form of mesh or mild steel bars, is properly lapped, with a minimum overlap of 450mm. Additionally, the reinforcement must be encased in a concrete cover of at least 40mm to protect it from the elements and ensure its longevity. Simply "treading in" the reinforcement during the concrete pour is not an appropriate method, as it may compromise the reinforcement's integrity and the structure's overall strength.

The raft's edge must be carefully detailed to accommodate the proper placement of the damp course and membrane. This may involve creating a "step" in the concrete at the raft's edge, ensuring a seamless integration of these crucial waterproofing elements. Proper damp coursing and membrane positioning are essential in preventing moisture from seeping into the building, which can lead to a host of structural and health issues.

In many cases, adding insulation over the raft, followed by a concrete or raised floor, is common. This helps to enhance the thermal efficiency of the building, reducing energy costs and improving the overall comfort of the occupants. However, drainage systems and geotextile barriers may be necessary in certain situations to prevent the clogging of free-draining materials by surrounding soil.

It is important to note that a structural engineer may not always have a comprehensive understanding of the intricacies involved in damp coursing, cold bridging, or land contamination issues. Therefore, ensuring that the structural engineer is fully aware of these details before construction begins is crucial. Failure to address these considerations can lead to significant challenges, as once the concrete is poured, it can be incredibly difficult to overcome any deficiencies or issues that arise.

Conclusion

Piled Raft Foundation is a leading specialist foundation and piling company that offers comprehensive piling services for both domestic and commercial clients. Our team of highly experienced professionals is expert in installing high-quality foundations for a wide range of projects.

Our commitment to building strong relationships with our clients is unparalleled. We pride ourselves on our complete transparency, ensuring you can trust us to deliver a stellar final product every time. From the initial consultation to the project's completion, we will take the time to understand your needs and requirements thoroughly. We'll visit your site to assess the situation and assign you a personal project manager who will be with you every step.

At Piling Raft Foundation, we are confident in providing exceptional value for money. Our competitive prices are accompanied by a comprehensive service that will exceed your expectations. When you choose Piling Raft Foundation, you can rest assured that you are partnering with a trusted and reliable foundation and piling specialist.

Foundations are often too weak to support the weight of a superstructure alone. However, robust methods exist to reduce the intensity of loads and fortify the soil. One of the most widely used deep foundation techniques worldwide is piling. Modern piling solutions are highly advantageous to construction projects because they are the most efficient method for deep foundations.

How are Piles used within Construction?

Piles are the foundation of deep construction projects. Piles are the solution when the soil's load-bearing capacity is insufficient to support the building's weight. By driving or drilling piles through the ground to a depth of solid earth, the loads are efficiently transferred to the underlying soil.

Piling is a critical technique for ensuring the structural integrity of buildings above and below ground. Piling rigs are inserted into the earth down to the bedrock, providing a secure and stable base to support the weight of the entire structure. Additional attachments, such as conical tips, are often welded to the pile ends to enhance their driving capability, as specified by the project contractor's design requirements. It is a proven and essential method for transferring the building's weight to the underlying soil, guaranteeing the safety and stability of the structure.

The Birth of Piling

Piling has been the foundation of construction since prehistoric times. When faced with weak, marshy soils near rivers and lakes, our ancestors used timber piles to fortify the ground and safeguard settlements. From the Swiss lake dwellers to villages across Britain, piling has long been the solution to build on challenging terrain.

Today, the relentless demand for developable land has driven governments and organizations to utilize properties with poor soil quality. Piling is now integral to modern construction, providing the sturdy foundations required for our built environment. This robust technique has stood the test of time, evolving alongside the demands of advancing civilizations.

The history of piling is one of resilience and innovation, as humanity has continuously adapted this method to overcome the limitations of the landscape. It is a testament to the ingenuity of our forebears and the vital role piling continues to play in shaping the infrastructure of the modern world.

What are the types of Piling?

Building engineers must rigorously evaluate the parameters of their construction site, including the soil, climate, and other critical elements, before decisively determining the appropriate piling type. To fully comprehend the scope of their infrastructure project, they must engage directly with architects. This essential knowledge enables them to confidently plan for effective building solutions and select the ideal piling type. The two primary forms of piling used in construction are friction piles and end-bearing piles, and engineers must choose the most suitable option with unwavering conviction.

Friction Piles

Friction piles effectively withstand the loads placed on buildings by harnessing the power of skin shear stresses. The surface of the pile adheres to the surrounding soil, creating a robust friction or adhesion that allows the entire pile surface to resist the load efficiently. This friction-based mechanism also reduces the bulb pressure on the pile surface. A cylindrical pressure zone forms around the pile surface when utilizing friction piles, further enhancing the pile's capacity to support the structure.

End Bearing Piles

End-bearing piles are a powerful solution for transmitting superstructure loads from weak strata, such as rock or extremely dense sand and gravel, to strong strata with higher bearing capacities. These piles rely on the resistance of the dense soil layer at the pile's end as the primary indicator of their load-bearing capabilities. To fully exploit the ultimate strength of the underlying layer, the pile's end must be embedded at least three times the pile's diameter into the hard strata. End-bearing piles can be swiftly constructed using prefabricated piles, making them a reliable and efficient choice for construction projects.

What are the Pile Construction Techniques?

Diverse soil types and structural requirements demand various reliable pile types. The fundamental design purpose determines the appropriate pile technique to be employed.

Driven Piles, Aggregate Piles, Bore Piles, and Screw Piles offer robust solutions tailored to specific project needs. Engineers must confidently select the most suitable pile type to ensure any construction endeavor's structural integrity and safety.

Driven Piles

Driven piles, or displacement piles, are the premier choice for deep foundations. They effortlessly transfer the weight of structures to robust rock or soil strata, ensuring unwavering support and optimal settlement properties. This economical deep foundation method is the go-to solution for buildings, walls, towers, and bridges. Driven piles also excel in cofferdam and anchorage applications. Furthermore, they are unparalleled for retaining walls, bulkheads, and embankments.

Bore Piles

Replacement or bore piles are the go-to solution for building foundations. They can support structures by transferring their weight to the most suitable soil, ensuring a sufficient bearing capacity. Bore piles are created by removing debris and forming a hole into which reinforced concrete is poured. In contrast to displacement piles, which push the soil aside, replacement piles replenish the spoil. Bore piles are the preferred choice for cohesive subsoils, enabling the creation of friction piles and the construction of pile foundations adjacent to existing structures.

Two highly effective methods of bored pile foundations are widely utilized: rotary bore and CFA piling. These techniques provide a decisive, reliable, and versatile solution for constructing robust foundations that can withstand the demands of modern structures.

Rotary Bore Piling

Rotary bore piling is the premier solution for construction companies facing severe ground impediments. This piling rig swiftly installs a robust temporary shell to provide unwavering support for the structure. A revolving cage is forcefully driven into the unstable soil to reinforce it, and the pile is then extracted using a powerful auger unit. Once the bore has been meticulously cleaned to the precise depth and the pile firmly inserted, the casing is resolutely removed, leaving the unyielding pile in place. Rotary Bore Piles are the definitive choice to fortify the ground, ensuring it can confidently bear the structure's load to be erected. In this decisive method, drilling is assertively conducted to the designated depth using a crane-mounted or track-mounted hydraulic drill.

Screw Piles

Screw piles feature a helix near the pile toe, enabling them to be efficiently driven into the earth. Depending on the application and soil conditions, screw piles may incorporate multiple helices, known as screws. Additional helices are incorporated to enhance performance when heavier loads or softer ground are encountered.

High-powered hydraulic motors apply substantial torque to drive screw piles deep into the soil. Rigorous engineering is required to optimize the interface between the pile and the supported structure. Key considerations include the building and the ground conditions for installing the piles.

The most common method of connecting screw piles to a building's foundation is by casting the pile head directly into the concrete footing. This is achieved by embedding steel reinforcing bars into the piles, with the bars extending into the building's foundation.

Aggregate Piles

Aggregate piles are powerful columns of compacted stone erected in groups within poor soil to boost bearing pressure and minimize settlement under structural footings. These robust installations, known as Bibro stone columns or rammed piles, are collectively called aggregate piles. The materials used in aggregate piles enable rapid construction, making them a highly cost-effective solution for building on soft soils. To create a dense bulb, the aggregate is forcibly driven into a casing, leaving no doubt about the strength and efficiency of this approach.

What are the Pile Installation Techniques

There are numerous techniques for installing piles, and each must be chosen according to the specific soil conditions. The depth of the excavation, the materials used for the piles, the steepness of the pile driving, and any environmental factors are critical variables that determine the appropriate installation method.

Installing displacement piles involves driving them directly into the earth without removing soil or other materials. Driven piles must be hammered, jacked, or vibrated into the ground to overcome the underlying soil resistance and allow the pile to slide smoothly into place. Specialized tools such as percussive hammers, hydraulic motors, and rams are essential.

Careful consideration of the relevant factors and the judicious application of the proper techniques are paramount to the successful and reliable placement of piles.

Deep foundations are a must for tall buildings. The higher the building, the stronger and more profound the foundations need to be. High-quality, heavy foundations are necessary for multi-story constructions. On the other hand, shorter buildings that spread out horizontally can suffice with shallower foundations. Choosing the correct foundation is crucial for a stable and safe construction that won't experience subsidence. 

If you have experience constructing houses with toy blocks, you are likely aware of the significance of getting the foundations right. Without a strong foundation, anything built on top is at risk of instability. Whether you are building a new structure or extending an existing property, the type of foundation required will vary. It is important to consider the specific needs of your project to ensure stability and safety. 

Some of the most common types of foundations used in construction are Pile foundations and Raft foundations.

Pile Foundations

Pile foundations are often utilized when heavy structures need to be supported in areas with weak soil. This type of foundation involves driving piles deep into the ground to transfer the building's load to more stable soil underground. Piles can be driven into the ground or cast in place, and a pile cap connects groups of piles to distribute the building load effectively.

Several types of piles are used in foundation construction, each serving a specific purpose. The types include end-bearing piles, friction piles, mini piles, and screw piles. Each type has its unique benefits and applications depending on the specific needs of the building project.

It is important to note that pile foundations require specialized knowledge and expertise for installation. Therefore, it is recommended that skilled professionals be consulted to ensure the proper installation and effectiveness of the pile foundation. While pile foundations may be more costly than other foundation types, their durability and efficiency make them a valuable investment for long-term stability and structural integrity. 

Raft Foundations

Mat foundations, also known as raft foundations, are concrete structures designed to support the entire footprint of a building. They are commonly used for one—or two-story buildings or where a basement is desired, making them a popular choice for residential properties. While they are relatively easy to construct and cost-effective, it is important to note that they may be susceptible to erosion at their edges. In instances where heavy reinforcement is required in specific areas, alternative foundation options may be more suitable.

What is the difference between the two?

Raft foundations are suitable for shallow foundations, while pile foundations are ideal for deep foundations. Raft foundations consist of a concrete mat on or above the ground, spread across the entire building area to support heavy structures. On the other hand, pile foundations focus on either a pile group or a pile cap as key components.

It is essential to consider that while raft foundations may be cost-effective in the short term, pile foundations are designed for long-term durability. Pile foundations are particularly beneficial for soft soil conditions, whereas raft foundations may require additional soil improvement measures such as Sand Compaction Pile, leading to project delays.

Both types of foundations have advantages, but pile foundations are often preferred for their stability and longevity, especially in soft soil environments.

Conclusion

To determine the appropriate foundations for your construction project, you must schedule a consultation with a qualified groundworks expert. They will assess the soil conditions and building size to recommend whether pile or raft foundations suit your needs. Contact us now to schedule a free, no-obligation quote and secure your groundwork solution.

What is Piling?

Piles are essential structural components that firmly transfer loads from a building or structure to stable layers of soil or rock. These long columns, constructed from steel, concrete, or timber, are strategically placed into the ground to support the structure. Pile foundations are the go-to choice for situations where surface soils are inadequate for bearing load or where structures need support on soft soils or slopes. This blog will explore the rich history of piling and the various types and materials used in construction.

History of Piling

The use of pile foundations dates back thousands of years, with the ancient Greeks and Romans utilizing wooden and stone piles to support their impressive structures. In Switzerland, a 6000-year-old building stands as a testament to the effectiveness of wooden piles in supporting heavy brick and stone structures on soft ground. The Romans, known for their engineering prowess, also used pile foundations to support grand constructions like bridges, aqueducts, and the iconic Colosseum in Rome.

During the medieval period in Europe, pile foundations were essential in constructing towering cathedrals and imposing castles. The sound of a heavy hammer driving wooden piles into the earth echoed throughout the medieval countryside as skilled craftsmen carefully laid the foundation for these architectural marvels.

The 19th Century brought advancements in construction materials, with concrete and steel becoming popular for pile foundations. Steam-powered pile drivers revolutionized the construction industry, allowing for deeper piles and heavier loads to be supported. Sturdy and reliable pile foundations made impressive structures of this era, such as sprawling industrial buildings and towering bridges, possible.

As we entered the 20th Century, hydraulic pile drivers took center stage, further increasing the efficiency and effectiveness of pile foundations. These specialized equipment allowed engineers to carefully drive piles into the earth with precision carefully, ensuring the stability of the structures they supported. From ancient times to the modern era, pile foundations have played a crucial role in constructing some of the world's most impressive buildings, testament to human ingenuity and innovation.

When construction on soft or unstable soil occurs, it is crucial to ensure that the foundation is solid and stable to support the weight of the building, bridge, highway, or other structure. This often involves complex engineering techniques such as soil stabilization, pile driving, and soil compaction. These methods help strengthen the ground and prevent settling or shifting that could compromise the integrity of the structure.

Imagine a team of engineers and construction workers meticulously planning and executing each process step, carefully maneuvering heavy machinery and equipment to prepare the site. Giant drills bore deep into the ground, inserting steel piles that will support the structure's weight above. Dump trucks unload tons of gravel and other materials strategically layered and compacted to create a stable base. The noise of machines reverberates through the air as workers hustle to meet deadlines and ensure that every detail is perfect.

As the foundation takes shape, it becomes apparent that this is no ordinary construction project. It is a feat of engineering precision and ingenuity, a testament to human innovation and determination. The finished structure will stand as a testament to the skill and dedication of those who worked tirelessly to make it a reality. As the final beams are put in place, the sense of accomplishment is palpable, knowing that this building, bridge, or highway will withstand the test of time thanks to the solid foundation laid on soft or unstable soil.

Types of Pile Foundations

End-Bearing Piles:

These piles are specifically engineered to transmit the full load of the structure directly to a solid layer of rock or extremely dense soil at the base of the pile. Comprised of durable materials such as concrete or steel, they are commonly utilized in structures with substantial weight requirements, such as tall buildings, bridges, and transmission towers. These piles are forcefully driven into the ground using a pile driver until they firmly anchor into the hard layer, ensuring maximum support and stability.

Friction Piles:

Engineered to shift the structure's load onto the surrounding soil through sheer friction, these piles are ideal for soft or insufficiently thick soil conditions. Constructed from sturdy materials like concrete or steel, friction piles are forcefully driven into the ground until the desired depth is achieved, establishing a strong bond between the pile and the soil to support the structure effectively.

Compaction Piles:

Compaction piles are designed to enhance the load-bearing capacity of loose or weak soils by effectively compacting the soil around the pile to bolster its strength. Crafted from precast concrete or steel, they are driven into the ground with precision using a pile driver until they reach the desired depth, ensuring improved stability and support for the structure above. The soil around the pile is forcefully compacted using a vibrating hammer to increase density significantly.

Anchor Piles:

Anchor piles are specifically engineered to support structures facing uplift forces, such as tall buildings or bridges. They are composed of sturdy steel and securely anchored to solid rock or dense soil layers using steel cables or rods rigorously driven into the ground.

Sheet Piles:

Sheet piles are designed to offer lateral solid support for excavations, retaining walls, and cofferdams. Made of robust steel or concrete, these piles are firmly driven into the ground to form an unyielding continuous wall, especially in areas with limited excavation space.

Bored Piles:

Bored piles are meticulously created by drilling deep into the soil and pouring substantial concrete into the hole. These piles, made of reinforced concrete, are commonly utilized in challenging soil conditions or areas with constrained headroom. They can act as both end-bearing and friction piles.

What are the different materials for Piling

Several materials can be used for piling foundations, each with unique characteristics and advantages. Concrete piles, for example, are solid and can withstand heavy loads, making them ideal for structures that need to support a lot of weight. They can be pre-cast in a factory, driven into the ground, or cast on-site for a more customized solution. On the other hand, steel piles offer excellent corrosion resistance and are perfect for structures in challenging soil conditions. Their versatile nature makes them suitable for various projects, from small buildings to significant infrastructure developments.

Some may consider Timber piles old-fashioned, but they remain a popular choice for light structures and soft soil conditions. Their natural properties make them easy to work with, and they can easily be cut to the desired length, providing a more sustainable option for some projects. Composite piles, on the other hand, offer the best of both worlds by combining materials like concrete and steel to create a strong and corrosion-resistant pile.

One of the more unique options for piling is the screw pile. These piles are made of steel and are screwed into the ground using specialized equipment. This method is particularly well-suited for light structures and soils that are easy to penetrate, providing a quick and efficient solution for foundation work. No matter which material is chosen, selecting the best option for the specific project requirements is vital to ensure a stable and long-lasting foundation.

Classification of Piles

According to the British Standard Code of Practice for Foundations, large displacement piles can come in various forms, each with unique characteristics and benefits. One type of large displacement pile is the round or square timber pile, often used in construction projects for its strength and durability. Another common type is the pre-cast concrete pile, which can come in solid or tubular sections and is known for its stability and load-bearing capacity.

Prestressed concrete piles are also popular, reinforced with tensioned steel cables to increase their strength and resilience. Steel tube piles, which can be driven with a closed-end, are a versatile option offering high stability and support. Fluted and tapered steel tube piles are designed to maximize their load-bearing capacity, making them a reliable choice for various construction projects.

Steel box piles with closed ends offer a secure and solid foundation for structures. Jacked-down solid concrete cylinders and steel tubes with closed ends provide additional options for large displacement piles, each offering a unique set of advantages for different types of construction projects.

Large Displacement Piles are a type of foundation that includes Driven and Cast-in-situ piles. These piles consist of pre-cast concrete shells filled with concrete, providing a sturdy foundation for structures. The process involves driving a steel tube into the ground and then withdrawing it after the concrete has been placed, leaving behind a solid pile that can support heavy loads. Another method involves a thin-walled steel shell driven into the ground using a withdrawable mandrel and then filled with concrete, ensuring a strong and stable building foundation.

In contrast, Small Displacement Piles are characterized by thinner tubular sections and open ends. These piles can be constructed using prestressed concrete or pre-cast concrete with tubular sections, providing a cost-effective solution for foundation support. Alternatively, steel tube sections or H-sections can be driven into the ground with an open end to create a stable foundation. Steel box sections are another option, offering durability and strength for structures that require a reliable foundation. These different piles offer versatile solutions for building foundations, ensuring stability and support for various structures.