Underpinning Historical and Heritage Buildings: Old and New Methods

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28 Jun 2024

Underpinning Historical and Heritage Buildings: Old and New Methods

Introduction

Image from Ultimate Handyman

Underpinning is a critical process in the field of construction, especially when it comes to preserving the structural integrity of historical and heritage buildings. As these buildings age, their foundations may deteriorate or prove inadequate due to changes in soil conditions, increased load demands, or other environmental factors. Underpinning involves strengthening and stabilizing the foundations to ensure the buildings' longevity and safety. This article explores both traditional and modern underpinning methods, with a focus on their application to heritage and historical structures.

Traditional Methods of Underpinning

Historically, underpinning methods were often labor-intensive and involved substantial disruption to the building's structure and surroundings. Some of the traditional techniques include:

1. Mass Concrete Underpinning:

This method, dating back to the early 20th century, involves excavating a series of pits beneath the existing foundation and filling them with concrete. This effectively extends the foundation depth, providing additional support. While effective, this method is time-consuming and requires significant excavation, which can be problematic for fragile historical buildings.

Image from the contractor

2. Beam and Base Method:

This technique involves constructing a reinforced concrete beam under or alongside the existing foundation. The beam is supported by a series of concrete bases or piers. This method provides a higher level of support and is less disruptive than mass concrete underpinning. However, it still requires considerable excavation and can pose risks to the structural integrity of delicate heritage buildings.

Image from the contractor

Modern Methods of Underpinning

Advancements in technology and engineering have led to the development of less invasive and more efficient underpinning methods. These modern techniques are particularly valuable for heritage and historical buildings, where preserving the original structure is paramount.

1. Mini-Piled Underpinning:

This method involves the installation of small-diameter piles (mini-piles) around and beneath the existing foundation. The piles are drilled deep into the ground, bypassing weak soil layers and reaching stable strata. This technique is less disruptive and can be carried out in confined spaces, making it ideal for heritage buildings. An example of its application is the stabilization of the historic St. Pancras Renaissance Hotel in London, where mini-piles were used to underpin the structure without disturbing its intricate architecture.

Image from larceny piling

2. Jet Grouting:

Jet grouting involves injecting a high-pressure jet of grout into the ground to form a series of overlapping columns. These columns create a stable support for the foundation. Jet grouting can be precisely controlled, minimizing disruption to the existing structure. The technique was effectively used in the underpinning of the Leaning Tower of Pisa, where it helped to stabilize the tower without altering its appearance.

https://images.app.goo.gl/ZhAvTL1rfX1KGtPUA

3. Micropiling:

Similar to mini-piling, micropiling uses even smaller diameter piles and is suitable for buildings with very limited access. The piles are drilled into the ground using specialized equipment, providing support without the need for extensive excavation. The technique has been used in the restoration of numerous historical buildings, including the Cathedral of Christ the Saviour in Moscow.
Image from scienceDirect.com

Case Studies

1. The Leaning Tower of Pisa, Italy:

The Leaning Tower of Pisa, an iconic historical structure, faced significant foundation issues due to unstable soil conditions. Traditional underpinning methods would have been too invasive for this fragile monument. Instead, a combination of soil extraction and jet grouting was used to stabilize the foundation. This approach successfully halted the tower's tilt and preserved its historical integrity.

2. The Palace of Westminster, London:

The Palace of Westminster, home to the UK Parliament, required extensive underpinning due to subsidence. A combination of traditional and modern methods was employed. Mass concrete underpinning was used in less critical areas, while mini-piling provided support to more delicate sections of the building. This hybrid approach ensured the preservation of the structure's historical features.

3. The Woolwich Arsenal, London:

This historic military site underwent redevelopment, necessitating the stabilization of several old buildings. Micropiling was chosen due to its minimal impact on the existing structures. The project successfully preserved the heritage buildings while allowing for modern redevelopment.

Conclusion

Underpinning is a vital process for maintaining the structural integrity of historical and heritage buildings. While traditional methods like mass concrete underpinning and the beam and base method have their place, modern techniques such as mini-piled underpinning, jet grouting, and micropiling offer significant advantages. These advanced methods are less invasive, more efficient, and better suited to the delicate nature of heritage buildings. Through careful planning and the use of appropriate underpinning techniques, we can preserve our architectural heritage for future generations.
For more on traditional underpinning, check out this YouTube video