GMR – Uncertainty of geological forecasts

The realisation of models and forecasts on the geological setting for tunnels design is among main activities of GDP-GEOMIN. Owing to the complexity of the buried geological context and to limited possibility of having access to direct information, unless punctual or extrapolated from surface, forecasts on geological setting always have an uncertainty, implying a variable degree of reliability.
Uncertainties on geological reconstructions can have a strong incidence on underground works completion, in terms of costs, timing and environmental impact.
Being aware of these problems and in order to provide its clients a service with high standards, GDP-GEOMIN developed and refined a methodology to evaluate the geological forecasts reliability for underground works.
The methodology is known as GMR – Geological Model Rating and consists of a parametric analysis of elements contributing to the construction of a predictive geological model, namely:

• The quality of available investigations;
• the complexity of geological context;
• the quality of methods applied for the interpretation.

Details of the method are available in some publications produced starting in 2011 (Perello, 2011) whose references can be found at the following link .
To date the method’s application can be done by means of a common Excel file properly pre-structured, that can be downloaded here. GMR allows to define, by stretches of appropriate length, the model reliability degree in terms of indeterminacy of position and extent of foreseen geological elements, as well as in terms of possible existence of unforeseen and critical geological elements.
Developments of the method by means of GIS (Geographic Information System) application are currently ongoing, aiming to an evolution of GMR through a larger automatization and a better spatial definition, not limiting the reliability estimate to a specific alignment.