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Grade 2 listed church stabilised in two days, avoiding risky underpinning

Challenge

A 12th-century Grade 2 listed church was suffering significant structural movement and cracking from clay shrinkage. Traditional underpinning posed a high risk of damage to the historic fabric and required weeks of disruption.

Solution

Geobear injected a specialist geopolymer to a depth of 2m to compact the clay soil. The work was completed in just two days, with zero disruption to the church.

2 days

Project completion time

Grade 2

Listed Historic building

24%

Improvement in bearing capacity, verified by SPT

Background

St Mary's Church in Doverdale, a Grade 2 listed building with 12th-century origins, was showing significant signs of subsidence.

Large cracks were forming in the walls of the East Wing. Geobear had previously stabilised the West Wing in 2012.

Challenge

Site investigations confirmed the movement was due to clay shrinkage, exacerbated by a large tree.

The church leadership and their consultants needed a solution to protect the building's integrity.

Traditional underpinning was a high-risk option as it could damage the historic foundations, would require large-scale excavation, and would disrupt church services for many weeks.

A fast, non-invasive, and proven solution was required.

 

Corner of St. Mary's Church at ground level with subsidence cracks visible between large brickwork

 

Geobear's fast, non-invasive solution posed no risk to the historic structure and caused no disruption to the church's operations.

A laser level in foreground with Geobear techs at work at the side entrance exterior of St. Mary's Church

Solution

Based on the site investigation data, Geobear's engineers designed a targeted geopolymer injection solution for the East Wing. Shallow trenches were used to expose the foundations, and a specialist resin was injected to a depth of 2m.

The geopolymer expanded to compact the clay soil, preventing the "shrink-swell" movement.

The work was monitored in real-time with lasers to verify stabilisation (registering 0.5mm of movement) and ensure no lift occurred.

Standard penetrometer testing results

Depth of treatment BGL (m) Injection level SPT N1(60) before treatment Cu (kPa) before treatment Current allowable bearing capacity (kPa) before treatment SPT N1(60) after treatment Cu (kPa) after treatment Expected allowable bearing capacity after treatment(kPa) % Improvement bearing capacity
0.8 1 9 46 89 12 60 111 24.7
1.3 2 21 104 210 24 118 238 13.3
1.8 3 22 110 231 25 124 257 11.3

Results

A series of injection points with safety barrier and generator at exterior of St. Mary's Church

The stabilisation work was completed in just two days. Post-treatment Standard Penetrometer Testing (SPT) confirmed the ground's bearing capacity had improved by 24% at the key level.

The structural movement was arrested, and the church was protected from further damage.

The fast, non-invasive solution posed no risk to the historic structure and caused no disruption to the church's operations.

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