Underpinning: The Foundation Solution That Works

In order to understand underpinning, it’s important to understand what we mean by the foundation and why it makes a good solution.  

The foundation is the base upon which a building or structure is constructed. It is the lower part of the building that is in direct contact with the ground, and it is designed to transfer the load of the building into the ground.  

The foundation is a critical element of the construction of any building or structure, as it supports the weight of the entire structure and helps to keep it stable.  

At CGI Solutions we have more than 14 years’ experience in underpinning Perth foundations and recognise the significant benefits it offers to different foundation types. 

FOUNDATION TYPES 

There are several types of foundations that can be used in construction, including shallow foundations, deep foundations and piled foundations.  

The type of foundation used will depend on the soil conditions, the size and weight of the structure, and the design of the building. A structural engineer or foundation specialist will be able to advise on the most suitable type of foundation for a particular project. 

UNDERPINNING TECHNIQUE 

Underpinning is a technique that is used to strengthen or repair the foundations of an existing building or structure. It is typically used when the original foundations are not sufficient to support the structure, or when the soil conditions have changed and the foundations are no longer stable. 

Underpinning can be used in conjunction with both shallow and deep foundations. For example, if a building has shallow foundations that are no longer sufficient to support the structure, underpinning can be used to strengthen the foundations by adding additional support below the existing foundations.  

On the other hand, if a building has deep foundations that have become unstable due to changes in the soil conditions, underpinning can be used to repair and stabilise the foundations. 

There are several methods of underpinning, including mass concrete underpinning, piling, grouting. The most suitable method will depend on the specific circumstances of the project. 

For specific information relating to underpinning Perth and Western Australia please take a look at the latest state Building Regulations legislation. 

CONSIDERATIONS FOR STRUCTURAL ENGINEERS 

Structural engineers must take a number of factors into consideration when assessing the feasibility and suitability of underpinning for a construction project.  

Some of the key considerations include: 

1. The condition of the existing foundations:

The engineer will need to assess the condition of the existing foundations to determine whether they are capable of supporting the structure, or if they need to be strengthened or repaired. 

2. The soil conditions:

The engineer will need to assess the soil conditions to determine the stability of the ground and the load-bearing capacity of the soil. This will help to determine the type of underpinning that is most suitable for the project. 

3. The size and weight of the structure:

The engineer will need to consider the size and weight of the structure to determine the amount of support that is required and the most suitable type of underpinning. 

4. The design of the building:

The engineer will need to consider the design of the building, including any planned renovations or additions, to ensure that the underpinning is sufficient to support the structure as a whole. 

5. The cost and feasibility of the underpinning:

The engineer will need to consider the cost and feasibility of the proposed underpinning, including any potential disruptions to the building or surrounding area during the work. 

6. Any potential risks or hazards:

The engineer will need to assess any potential risks or hazards associated with the proposed underpinning, such as the possibility of undermining the stability of adjacent structures. 

UNDERPINNING METHODS 

There are several different methods of underpinning, including: 

1. Mass concrete underpinning:

This involves excavating beneath the existing foundation and pouring a new foundation of reinforced concrete. 

2. Piling:

Piling involves driving long, sturdy poles or piles into the ground to support the building. 

3. Beam and base:

This method involves installing a series of beams and concrete bases beneath the existing foundation to support the weight of the building. 

4. Grouting:

Grouting involves injecting a mixture of cement and water into the soil beneath the foundation to strengthen it. 

Underpinning is a complex and specialised process that should be carried out by trained professionals.  

It is important to carefully assess the condition of the foundation and choose the appropriate underpinning method to ensure the stability and safety of the building. 

Below is more detail on how home underpinning methods might vary.  

MASS CONCRETE UNDERPINNING 

Mass concrete underpinning is a construction technique used to strengthen and stabilise the foundation of a building. It involves excavating beneath the existing foundation and pouring a new foundation of reinforced concrete. 

This method is often used when the original foundation is not sufficient to support the weight of the building, or when the soil beneath the foundation has become unstable. It is also sometimes used to increase the height of the foundation to raise the building above flood level or to add additional floors to the building. 

To perform mass concrete underpinning or ‘hit and miss’, the following steps are typically followed: 

1. Excavation:

The area beneath the existing foundation is excavated to create a space for the new foundation. 

2. Rebar installation:

Reinforcing bars, or rebar, are placed in the excavation to provide structural support for the new foundation. 

3. Concrete pouring:

Concrete is poured into the excavation and allowed to cure. 

4. Backfilling:

Once the concrete has cured, the excavation is backfilled with soil to support the new foundation. 

Mass concrete underpinning is a complex and specialised process that should be carried out by trained professionals. It is important to carefully assess the condition of the foundation and choose the appropriate underpinning method to ensure the stability and safety of the building. 

PILING 

Piling is a construction technique used to strengthen and stabilise the foundation of a building. It involves driving long, sturdy poles or drilling piles into the ground to support the building. 

Piling is often used when the original foundation is not sufficient to support the weight of the building, or when the soil beneath the foundation has become unstable. It is also sometimes used to increase the height of the foundation to raise the building above flood level or to add additional floors to the building. 

There are several different types of piles, including: 

1. Concrete piles: These are made of reinforced concrete and are typically used in areas with high loads or high water tables. 
2. Steel piles: These are made of steel and are often used in areas with soft or unstable soil accompanied with anchors. 
3. Timber piles: These are made of wood and are typically used in temporary construction or in areas with low loads. 

To perform piling, the following steps are typically followed: 

1. Excavation: An excavation is made at the site where the piles will be installed. 
2. Pile installation: Piles are driven into the ground using a pile driver, a screw piler, augers or other specialised equipment. 
3. Grouting: A mixture of cement (Not Sand) and water is injected into the soil around the piles to strengthen the soil and improve the stability of the foundation. 

As with the previous methods outlined, piling is a complex and specialised process that should be carried out by trained professionals. It is important to carefully assess the condition of the foundation and choose the appropriate piling method to ensure the stability and safety of the building. 

BEAM AND BASE 

The beam and base approach to underpinning is a construction technique used to strengthen and stabilise the foundation of a building. It involves installing a series of beams and concrete bases beneath the existing foundation to support the weight of the building. 

This method is often used when the original foundation is not sufficient to support the weight of the building, or when the soil beneath the foundation has become unstable. It is also sometimes used to increase the height of the foundation to raise the building above flood level or to add additional floors to the building. 

To perform beam and base underpinning, the following steps are typically followed: 

1. Excavation: The area beneath the existing foundation is excavated to create a space for the new beams and bases. 
2. Rebar installation: Reinforcing bars, or rebar, are placed in the excavation to provide structural support for the new beams and bases. 
3. Concrete pouring: Concrete is poured into the excavation to form the beams and bases. 
4. Backfilling: Once the concrete has cured, the excavation is backfilled with soil to support the new foundation. 

It is important to carefully assess the condition of the foundation and choose the appropriate underpinning method to ensure the stability and safety of the building. 

GROUTING 

Grouting involves injecting a mixture of Micro-fine cement, and water into the soil to improve its stability and load-bearing capacity. 

Grouting is often used in conjunction with other underpinning methods, such as mass concrete underpinning or piling, to provide additional support to the foundation. It can also be used on its own to stabilise soil in areas where the foundation is already sufficient but the soil has become unstable due to factors such as erosion or settling. 

To perform grouting, the following steps are typically followed: 

1. Excavation: An excavation is made at the site where the grouting will be done. 
2. Holes: Holes are drilled into the soil at regular intervals. 
3. Injection: A mixture of cement, and water is injected into the holes using specialised equipment. 
4. Curing: The injected mixture is allowed to cure, strengthening the soil and improving its stability. 

Once again, grouting is a complex and specialised process that should be carried out by trained professionals.  

OUR EXPERIENCE UNDERPINS OUR SUCCESS 

For all your foundation problems in Perth, get in touch with us at CGI Solutions. We have more than 14 years’ and an additional 10 years’ experience retaining installation in all types of conditions and environments and have the capabilities you require to get the job done. Contact us today to discuss your project and find a solution quickly and affordably.