Is your building suffering from foundational issues? Underpinning can provide a robust solution to strengthen your structure.
By stabilizing the ground beneath their property, you can enhance its durability while preventing future disasters.
Underpinning has numerous benefits and can add value to your existing property. Improved bearing capacity of soil, corrected foundation settlement, and enhanced safety are some highlights.
Understandably, identifying the right approach for underpinning is crucial to get optimum results.
To learn more about underpinning and how it can give your building a strong stand, read more on GeoTech Built.
What is Underpinning?
Underpinning is a strategy to reinforce the existing foundation of a building, necessary when the initial foundation fails to adequately support the structure.
This often occurs due to changes in soil conditions, which can be affected by factors like moisture levels, tree roots, or damaged plumbing.
- Soil Expansion/Contraction: Changes in moisture levels or nearby trees can affect the soil’s capacity to support the foundation.
- Inadequate Original Design: Misunderstanding of soil properties during the foundation’s design can necessitate underpinning.
- Change in Structural Use: Major renovations or additional loads may require extra support.
- Natural Disasters: Events like earthquakes or floods can destabilize structures, making underpinning necessary.
To determine if your building needs underpinning and the most effective method, consult a structural engineer.
Your building’s foundation is essential; performing regular checks and addressing problems promptly can prevent severe consequences later on.
When is Underpinning Needed?
Underpinning strengthens existing foundations when they lack stability to support the house, often due to changes in soil structure.
| Reason for Underpinning | Signs of Need | Actions Required |
| Soil subsidence due to plumbing damages | Floors become uneven or sloping | Hire a structural engineer |
| Inadequate original soil assessment during foundation design | Cracks in walls or floors | Consult an underpinning specialist |
| Nearby construction affecting supporting soil | Gaps forming beside windows/doors | Schedule an inspection |
| Natural disasters causing instability | Doors and windows not fitting properly | Assess if underpinning provides a permanent fix |
Underpinning may also be necessary when building usage changes, such as during major renovations or when adding another level. Factors like soil types, site classifications, and footing types critically impact your foundation.
Types of Foundation Underpinning
The design and condition of your building determine the best underpinning method. Understanding each type helps in making a wise selection for foundation reinforcement.
Mass Pour Method is widely used due to its cost-effectiveness and ability to handle heavy loads. It involves digging sections beneath the foundations and pouring concrete, but it’s labor-intensive.
Mini-Piled Method suits sites with variable soil conditions and limited access areas, involving installation of slim piles at significant depths.
- Beam and Base Method: Builds a reinforced concrete beam below the existing foundation, transferring load evenly.
- Pit Method: Constructs a temporary foundation to bear the building’s weight while excavating beneath the existing one.
- Needle Beam Method: Uses micropiles close to the building, followed by needle beam excavation and casting.
- Micropiling Method: Builds micro-piles at an angle beneath the existing foundation before removing earth between it and the foundation’s bottom.
Other methods include Expanding Resin Injection, which compacts soil by injecting resin and hardener, and Jet Grouting, involving pressurized grout jets to stabilize soil.
Foundation underpinning is tailored to structural damage and soil types, regardless of repair scale.
Improving Foundation Stability
Underpinning enhances a building’s stability by improving the properties of the underlying soil or foundation.
Mass Concrete Underpinning
Also known as the Pit Method, it involves extending the old foundation to reach stable strata, increasing stability mechanically.
Mini Piled Underpinning
Applied to sites with variable soil conditions and limited access, using piles and needles to address soil settlement due to water or clay.
Bearing Micropiles and Footings
Provides robust support in challenging ground conditions, offering efficient, low-disruption solutions for sinking structures.
Limited Access Micropiles
Ideal for projects with restricted space, combining steel casing with micropile technology to enhance load-bearing capacity in complex geologies.
Additional Techniques
Techniques like grouting, deep foundations, compaction piles, geosynthetics, ground improvement, soil stabilization, and slurry walls also contribute to structural longevity and stability.
Soil Types and Classifications
The Unified Soil Classification System (USCS) classifies soils based on grain size: coarse-grained (gravels, sands), fine-grained (silts, clays), and highly organic soils (peat). This classification influences the underpinning process, as soil composition affects foundation stability.
Organizations like the Occupational Safety and Health Administration (OSHA) classify soils as ‘Type A’, ‘Type B’, and ‘Type C’ based on cohesive strength:
- Type A Soils: Cohesive soils with high unconfined compressive strength (e.g., clay), offering excellent stability unless disturbed.
- Type B Soils: Cohesive soils with moderate strength (e.g., silt, gravel), stable but sensitive to vibration.
- Type C Soils: Cohesive soils with weak strength (e.g., sandy gravel), posing more risk and often requiring extensive underpinning.
Knowing your soil type is crucial before underpinning to ensure an effective and lasting solution for foundation problems.
Why Foundations Fail
Understanding why foundations fail is essential for prevention.
Soil Type
Soil beneath the building significantly influences the foundation. Expansive clays can swell, causing differential settlement and structural damage.
Compaction of Fill Material
Insufficiently compacted fill can cause uneven settlement, leading to foundation problems.
Slope Failure/Mass Wasting
Downhill earth movement exerts pressure on foundations, leading to failure. Underpinning can prevent slope failures if properly designed.
Erosion
Erosion removes soil around a foundation, creating settlement problems that may necessitate underpinning. It can result from poor drainage or unregulated water flow.
Poor Construction
Inadequate engineering and insufficient soil testing during construction can lead to failing foundations. Adherence to building codes can prevent such issues.
Transpiration
Transpiration, where plants absorb soil moisture, can cause soil shrinkage, leading to differential settlement and foundation failure.
Benefits of Underpinning
Underpinning reinforces existing foundations, boosting a building’s stability and lifespan.
What Does Underpinning Involve?
It entails adding a deeper foundation beneath the current one, equipping the structure with a superior base.
How Can Underpinning Prevent Damage?
Underpinning fortifies your building’s foundation, preventing costly damage from subsidence by installing additional supports.
When Would a Building Need Underpinning?
Buildings on unstable or low-quality soil may require underpinning to prevent movement and structural harm.
Can Underpinning Be Useful for Extensions?
Yes, underpinning provides extra safety when extending a building or supporting a heavier load.
What Benefits Can Underpinning Provide for Structural Stability?
Underpinning enhances the strength of existing foundations, improving safety and longevity, and is a cost-effective way to ensure stability.
Underpinning Techniques Explained
Underpinning improves and strengthens a building’s foundation by deepening the base. Several methods exist, chosen based on the structure’s needs and soil conditions.
- Pit Method: Involves digging soil carefully under the foundation using pins, then filling with concrete.
- Mass Pour Method: Entails pouring concrete beneath the existing foundation section by section.
- Beam and Base Method: Constructs a reinforced concrete beam below the footing, transferring the load evenly.
- Mini Piled Method: Suitable when loads need transfer to greater depths; involves driving steel piles filled with concrete or resin.
- Piled Raft Underpinning: Used when complete underpinning is necessary; piles form a grid with a concrete raft over them.
- Pier and Beam Method: Uses reinforced beams to transfer the load to piers, suitable for deeper foundations.
- Screw Pile Method: Supports weak foundations in water-logged or clayey soils using screw piles.
Choose the method based on factors like soil type and foundation weakness. Consult professionals for effective underpinning.
Steps in Underpinning Process
Underpinning in Australia involves unique steps.
Installation of Footings
Underpins or deep footings are installed where the house has sunk due to soft or loose soil that can’t be naturally repaired, providing reliable support.
Jacking Up the House
The house is carefully lifted with robust jacks, gradually bringing it back to level, ensuring safety while improving foundation strength.
Permanent Support with Underpins
Underpinning and stabilization are completed, and the house is permanently supported by underpins. Spaces left by jack removal are filled with steel plates and concrete, providing solid, enduring support.
Final Thoughts
Understanding and prioritizing proper underpinning for your building’s foundation can significantly improve its longevity and stability. By identifying signs of potential failure and choosing the correct method, you are now better equipped to protect your investment. For professional help, check out these services.
