Groundwater leakage into subsurface constructions, such as tunnels and shafts, can cause a drop of pore pressure in clay resulting in land subsidence with the potential of serious damage to buildings. New research gives better tools for mitigating the risks.
Even at large distances from the construction, groundwater leakage into tunnels, can cause a drop in pore pressure, subsidence and damage to buildings. The potential costs are huge and with the increasing need for tunnels to reduce traffic congestion in the world’s growing cities, these potential costs are on a rise.
A new study provides an innovative mapping method to reduce the risks. The study is based on the use of probability-based models.
Jonas Sundell, who works in COWI's hydrogeology department at the office in Gothenburg, and who is an industrial PhD student at Chalmers University of Technology in Sweden, explains:
“We looked into areas where there is a risk of subsidence, if you lower the groundwater level. These issues used to be addressed in a rather fragmented way; the geo-technicians drilled holes in certain places and the hydrologists examined other areas, but they could never tie the information together effectively. With the new method, they can do this. The method is probability-based and describes where in an area the risks may be found.”
The case study for the PhD is the City Link high voltage utility tunnel in Stockholm, Sweden. It demonstrates the efficiency and usefulness of this modelling approach as a tool for communication to stakeholders, decision support for prioritisation of risk-reducing measures and identification of the need for further investigations and monitoring. The method has also been used on the ‘Stockholm Bypass’ and the ‘West Link’ in Gothenburg.
“In this study, we looked at 20,000 bore-holes in central Stockholm. Some were for the electric cable tunnel covered by the case-study, and others for projects that we found in the city archive and with relevant authorities,” says Jonas.
He and his team’s work ‘Risk mapping of groundwater-drawdown-induced land subsidence in heterogeneous soils on large areas’ was recently published in the journal Risk Analysis.
The study is partly financed by COWIfonden.