Challenge
A vertical extension at Heathrow T3 required a 100% increase in foundation capacity. The traditional solution, concrete footing extension, meant a 2-month shutdown, major excavation, and high costs.
Solution
Geobear's in-house team used PLAXIS modelling to design a geopolymer injection solution. This increased the soil's bearing capacity from beneath the pads, all with zero excavation.
Project completed in 2 weeks vs. 2 months
To live airport operations
Versus traditional methods
Target Factor of Safety achieved, up from a failing 1.7
The client at London Heathrow Airport Terminal 3 sought to add additional storeys to an existing arrivals building.
The original foundations, designed for 160 kPa, were insufficient for the proposed vertical extension, putting the project's structural safety and serviceability at risk.
The structural upgrade required an increase in foundation capacity of up to 100%. The traditional engineering solution involved building reinforced concrete "flanges" to enlarge the footing area.
This method was "costly and challenging," requiring major excavation, temporary works, and a 2-month project timeline, all within a live, 24/7 airport terminal. The operational impact was unacceptable.
Steve Pinnegar, C&S Director, BakerHicks
Geobear was selected for its low-cost, fast-track, and non-disruptive solution. Our in-house design team used PLAXIS software to accurately model the ground and design a solution to meet the new load requirements.
We used geopolymer injection to increase the load-bearing capacity of the soil directly beneath the existing foundation pads.
This process required no excavation and was completed without any interruption to airport operations.
Numerical simulations confirmed the solution's success, showing the new load would have caused the Factor of Safety to drop to 1.7 (failing), but with the Geobear treatment, it was restored to a safe 2.4.
| Pad no. | Depth of foundation (m) | Required bearing Pressure (kPa) | Design dosage (kg) | Actual injected dosage (kg) | Current Avg SPT | Achieved Avg SPT | Avg soil modulus before injections (MPa) | Avg soil modulus after injections (MPa) | Settlement after injections after load increase (mm) | Improvement in soil modulus |
|---|---|---|---|---|---|---|---|---|---|---|
| D31 | 1.9 | 275 | 220 | 223 | 7 | 26 | 15.6 | 38.4 | 5.5 | 146% |
| D29 | 1.9 | 275 | 240 | 240 | 2 | 24 | 10.1 | 36 | 5.9 | 257% |
| D27 | 2.5 | 330 | 140 | 141 | 60 | 64 | 79.2 | 84 | 3 | 6% |
| D25 | 2.7 | 280 | 140 | 136 | 25 | 43 | 37.2 | 58.8 | 3.7 | 58% |
| D23 | 1.6 | 275 | 120 | 119 | 23 | 44 | 34.2 | 59.4 | 3.6 | 74% |
| A29 | 3.4 | 330 | 80 | 81 | 13 | 29 | 22.8 | 42 | 6 | 84% |
| A27 | 3.2 | 330 | 100 | 100 | 4 | 39 | 11.5 | 54 | 4.7 | 369% |
| A25 | 2.7 | 319 | 120 | 120 | 33 | 39 | 46.8 | 54 | 4.5 | 15% |
The allowable bearing capacity was calculated using a 3.5 Factor of Safety.
The allowable bearing capacity was calculated using the achieved average SPT post treatment.
The allowable bearing capacity was calculated using the depth of foundation found during coring.
The allowable bearing capacity was calculated using Terzaghi’s method for calculating the bearing capacity.
A foundation width of 1.5 was used in all calculations.
The project was completed in just two weeks—four times faster than the traditional alternative—and with zero disruption to passengers or airport operations. We successfully increased the load-bearing capacity of the foundation pads to the required target values, providing a solid, verified base for the vertical expansion.
The solution was also more sustainable, reducing the project’s carbon footprint by up to 60% by eliminating excavation and new concrete.
Don't let complex foundation work derail your project. Increase bearing capacity with no excavation, no downtime, and a predictable schedule.