In the context of an hydroelectric power system, the topic is about the unforeseen operational difficulties encountered during the construction of the diversion tunnel and the other related works (dam, penstock and powerhouse), built under more onerous conditions than foreseen. The main reasons that have prevented the expected carrying out of the works for the realization of the diversion tunnel are related to the following causes: – Unavailability and inaccessibility of the areas and access roads – Fragmented and delayed delivery of projects from the Supervisior – Different conditions between actual geological characterization and planned project In detail, general discrepancy appears conspicuous between the excavated sections and what was the expected geological situation on the project; moreover, other problems came out, such as significant water inflows, that have reduced the productivity of excavation and have required the adoption of unpredicted specific solutions. The Contractor has denounced since the beginning the design lacks that prevented it from proceeding with the work as planned in the tender. The final result has been a forced slowdown of the realization of planned works and the necessity of a continuous re-planning in terms of operating resources as well as an unexpected engineering support provided by the Contractor. These issues, chromatically shown, are positioned on a “time-price diagram”. The same board also includes the related economical consequences of the underproduction shown by the convergence between the economical curves of what was contractually expected and what was really realized; the latter shows lower productivity in the period immediately following the occurrence of unpredicted/unpredictable events. On the basis of all these detailed information, it is possible to achieve the evidence of the disruption and the consequent time extension, with the necessity to submit the economical claims in order to rebalance economically the whole contract.