UTILIZED SOFTWARE 

PLAXIS, PLAXIS 3D

LOCATION 

Portugal

ORGANIZATION/COMPANY 

LNEC (Laboratório Nacional de Engenharia Civil)

On the edge of Lisbon's Praça do Comércio stands a tower that has been quietly sinking for more than a century. Founded on soft alluvial soils, it had settled over half a metre, and monitoring between 1956 and 2019 recorded 153 mm of movement. The conventional response would have been decisive and invasive: micropiles, jet grouting, partial removal of the old foundation — heavy interventions that carry heavy consequences for a historic structure and for the ground beneath it. Traditional analytical methods could not resolve the three-dimensional interaction between soil and structure, nor the slow creep of soft soils under new loads, so uncertainty pushed the project toward over-engineering.

Instead, LNEC — a public research institution with more than seventy-five years of engineering experience — built a detailed three-dimensional finite element model in PLAXIS 3D, applying a Soft Soil Creep formulation to replay over a century of consolidation and calibrating it against the real monitoring record. The model reproduced the measured settlement, confirmed the tower was behaving as a rigid body, and forecast only 0.12 metres of further settlement by 2100. The evidence was clear: reinforcement was not needed.

The impact of that single, well-founded decision is substantial. Avoiding micropiles saved 150 to 250 tonnes of CO₂; avoiding jet grouting saved up to 2,000 to 3,000 tonnes. The alluvial soils and the groundwater systems within them were left undisturbed. Analysis time fell by roughly 30 percent and project costs by 25 to 35 percent. And the tower itself, spared from intrusive works, could be safely adapted for reuse as a museum — returning an iconic landmark to public life.

Sometimes the most sustainable construction is the construction that never has to happen.