January 05 2024 0comment

What is Foundation Underpinning?

Foundation problems can threaten the structural integrity of any building, potentially leading to serious damage and costly repairs if left unaddressed. This comprehensive guide explores foundation underpinning – a crucial solution for stabilising and reinforcing weakened foundations – and helps property owners understand when and why this intervention might be necessary.

Understanding Foundation Destabilisation

The stability of a building’s foundation naturally decreases over time. When movement exceeds the design limits of the footing, it creates additional stress that can cause cracking, bending, or rotation. These stresses transfer to the walls and concrete slabs above, potentially resulting in masonry cracks and, in severe cases, compromising the building’s structural integrity.

Warning Signs

While hairline plaster cracks are often cosmetic and require minimal attention, certain signs should prompt immediate investigation:

  • Stepped or long zigzag masonry cracks
  • Significant concrete cracks
  • Visible foundation movement
  • Cracks appearing along walls
  • Uneven or sloping floors

Common Causes of Foundation Problems

Poor Construction Methods

Buildings designed and constructed under qualified engineering supervision according to the Building Code of Australia (BCA) rarely experience construction-related foundation issues. However, problems often arise when:

  • Construction codes are not properly followed
  • Substandard materials are used
  • Contractors take shortcuts to save costs
  • Proper engineering oversight is lacking

Environmental Changes

Both natural and human-made environmental changes can significantly impact foundation performance. Key factors include:

  • Removal of large trees nearby
  • Changes in water table levels
  • Fluctuations in soil moisture content
  • Nearby excavation work
  • Local dewatering activities or water bore installation

Structural Modifications

Building modifications can compromise foundation stability:

  • Adding extensions without proper consideration of existing foundation capacity
  • Installing additional levels without upgrading foundations to handle increased loads
  • Changing the building’s purpose or usage patterns

Historical Building Considerations

Buildings constructed before the 1950s often used simpler foundation systems, such as:

  • “Brick on flat” systems (double-brick rows laid directly on sand)
  • Limestone blocks with brick cavity walls These rigid foundation systems weren’t designed to accommodate soil movement, making them particularly vulnerable to instability.

The Underpinning Solution

Foundation underpinning is an effective method for:

  • Increasing foundation depth
  • Reinforcing weakened foundations
  • Supporting additional structural loads
  • Addressing foundation damage
  • Stabilising soil movement

Modern Underpinning Techniques

While traditional methods like contiguous piling or shore piling are still used, modern techniques such as grout injection offer efficient solutions. This process involves:

  1. Direct injection of grout into the soil beneath existing foundations
  2. Formation of stabilising grout blocks
  3. Prevention of further sinking and subsidence

When to Consider Underpinning

Underpinning may be necessary when:

  • Foundation wooden piles have begun to decay
  • Building usage patterns have changed significantly
  • Soil properties have altered
  • Nearby construction activities affect soil stability
  • Foundation shows signs of failure or movement
  • Structural modifications require additional support

Professional Assessment and Implementation

Given the complexity and importance of foundation work, professional assessment is crucial. When selecting an underpinning service:

  1. Ensure they have relevant experience and qualifications
  2. Request detailed site assessments
  3. Ask for clear explanations of proposed solutions
  4. Obtain comprehensive cost estimates
  5. Verify their understanding of local building codes and regulations

Foundation underpinning is a vital solution for maintaining building stability and preventing structural failure. Early intervention when problems are first noticed can prevent more serious damage and reduce overall repair costs. Always consult qualified professionals for assessment and implementation of underpinning solutions to ensure the long-term stability and safety of your building.

For specific concerns about your property’s foundation stability or to discuss underpinning solutions, consult with experienced foundation specialists who can provide targeted advice for your situation.

How Much Does It Cost?

Here at BMC Microfine, we specialise in providing the most appropriate advice to our clients to ensure their project is a success.  The cost of underpinning can vary depending on a variety of factors so to get a better idea of price, feel free to give us a call on 08 9303 9297 to discuss more.

 

 

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