What Is the Pile Method of Underpinning? A Complete Guide
Did you ever speculate how buildings can last so long and withstand the elements of nature? There are very few methods that can be effective. One of these methods is the piled method of underpinning, a combination of engineering prowess and practical application that ensures your structure remains stable and sound. This method is frequently used when traditional underpinning methods are not suitable or affordable, particularly in cases of subsidence or weak soil.
Whether you are tackling sagging floors or cracking walls, you can save time, money, and reduce stress by understanding this specialised method. This process involves installing deep piles to transfer loads to more stable soil, ensuring lasting durability. In this guide, we will take a deep dive into what exactly the piled underpinning method entails, explore its benefits and applications, and examine the different types available for various needs.
What Is Piled Underpinning and How Does It Function?
Piled underpinning is a method used to strengthen or deepen the foundations of a structure by installing piles, which are long, sturdy columns, beneath the existing foundation.
Identifying the Requirements
Underpinning, including piled underpinning, is usually necessary when a building’s foundation is unstable due to subsidence or heave. This can result from various factors, such as soil movement, tree root interference, or poor initial foundation design.
Soil Examination
Before starting any work, conducting a comprehensive soil analysis is essential. This assessment involves evaluating the soil’s type, condition, and bearing capacity to determine the suitable depth and type of piles required for the project.
Pile Installation
Piles are installed through these piling techniques:
- Driven piles: Precast concrete or steel piles are driven into the ground with specialised equipment.
- Augered piles: Holes are drilled into the ground, and steel casings or reinforcements are inserted, followed by pouring concrete or grout to form the pile.
Transferring the Load
After installation, the piles are connected to the existing foundation, typically with steel beams or a reinforced concrete slab (raft). This link transfers the building’s weight from the unstable soil to the new piles, creating a more stable and dependable foundation.
Monitoring and Completion
Once the load is distributed, the site is carefully monitored to make sure the concrete cures properly and the new foundation remains stable.
Types of Piled Underpinning Methods
Piled underpinning techniques transfer a building’s load to deeper, more stable soil layers by using piles. The choice of a suitable underpinning method is based on soil type, the depth of stable soil layers, the building’s load requirements, and site accessibility. Some standard piled underpinning methods include:
Driven Piling
Driven piles are hammered or driven into the ground with special tools. These are often used in loose soils with high water tables or when dealing with polluted soil.
- Steel Cased Bottom Driven Piles: These deliver driving force directly to the pile’s toe, making them suitable for confined spaces.
- Steel Cased Grundomat Driven Piles: These use compressed air for installation, which helps reduce vibration.
Augered Piling
These piles require drilling a hole initially, followed by filling it with concrete or grout.
- Sectional Auger Mini Piles: Highly adaptable for restricted areas, offering flexible installation options.
- Continuous Flight Auger (CFA): Drilled in a single turn or hollow stem, it supports the sides of the hole.
- Helifix Dixie Pile: A screw-in pile with a helix shape, providing reliable end-bearing capacity and quick installation.
Mini-Piled Underpinning
This method involves driving or drilling small-diameter piles into the ground to reach stable soil layers.
- Augered Mini Piles: Steel tubes are inserted into the ground and filled with high-strength concrete.
- Driven Mini Piles: Precast, reinforced concrete piles are driven into the ground using a hammering technique.
Bored Piling
Bored piles are created by drilling a hole and subsequently filling it with concrete. This is commonly used when driven piles are not feasible.
- Rotary Bored Piling: A particular type of bored piling that uses rotary drilling techniques.
- Continuous Flight Auger (CFA) Piles: This involves a drilling process where an auger creates the pile bore, typically accompanied by the injection of grout.
Other Underpinning Techniques
Mass Concrete Underpinning (Pit Method)
A conventional method in which sections of soil beneath the foundation are excavated and filled with concrete.
Beam and Base Underpinning
Uses concrete beams supported by mass concrete bases strategically placed beneath the existing foundation.
Piled Raft Underpinning
Used for entire buildings, involving piles installed in a grid pattern after removing internal floors and foundation.
Resin Injection
A method of hardening the soil using resin, instead of building extra foundations.
Angle Piling
Piles are driven at an angle to provide support, often used in conjunction with walls.
Pile and Needle Beam
Piles are driven, and a needle beam is installed to transfer the load from the existing foundation to the piles.
Cantilever Pile and Beam
Akin to a pile and needle beam, but all work is done from the outside of the structure.
Advantages of the Piled Underpinning
Improved Structural Integrity
This method enhances stability by distributing loads to deeper, stable soil layers. This helps to prevent settlement, cracks, bumpy floors, and tilting. It is ideal for buildings on unstable ground or in areas prone to subsidence.
Minimal Disruption
Piled underpinning requires less excavation as compared to conventional underpinning methods. This makes it ideal for urban areas, heritage sites, or restricted-access sites. It produces minimal noise, dust, and vibration, allowing residents to stay in place while the project goes on.
Flexibility in Difficult Soil Conditions
This method is versatile, suitable for various soils, including clay, sand, silt, and soft ground. Experts from renowned companies can select mini piles, helical piles, or concrete piles based on the site’s specific needs. This adaptability makes this method perfect for earthquake- or flood-prone areas.
Durability
The piles are made from premium materials such as concrete, steel, or treated wood that resist corrosion and environmental stress. Once these piles are installed, you can expect the stable foundations to perform well for decades.
Cost-Effectiveness
While the primary cost may seem higher, its long-lasting savings can compensate for these expenses. Addressing core foundational issues prevents the need for expensive repairs later. Additionally, it allows for vertical expansion, enabling the addition of extra floors without requiring a new foundation. This helps to reduce expenses and optimise space.
When is Piled Underpinning Used?
Piled underpinning is a preferred method for resolving various problems:
Subsidence: When a building’s foundation sinks or relaxes because of soil erosion, piled underpinning can offer the necessary support and stability.
Weak or Unstable Soil: In case the soil beneath the foundation is weak, soft, or compressible, piled underpinning can distribute the building’s load to a stable soil layer or bedrock.
Deep Excavations: When traditional underpinning requires excessive depth, piled foundations offer a more practical alternative.
Limited Access: In situations where access to the site is restricted, piled underpinning using mini piles or screw piles can be a feasible option.
Environmental Considerations: Piled underpinning can be an eco-friendlier option than some traditional methods, particularly in sensitive areas.
Heavy Loads: For structures with heavy loads, such as high-rise buildings or bridges, piled foundations are often essential to distribute the weight effectively.
Existing Structures: This method is used to support and stabilise the foundations of existing structures, particularly when they exhibit distress.
Bottom Line
The piled underpinning is a highly effective method for stabilising and strengthening existing structures. This blog helps you explore different types of piled underpinning and the benefits of choosing this approach for various foundation issues, ensuring safety and longevity. By selecting this method, property owners and engineers can make informed decisions about structural repairs and renovations.
