## 4 Discussion
Failure to align the scope of geotechnical investigations with the geological complexity and sensitivity of the project leads to underestimation of risks, which, in turn, increases the likelihood of structural errors and costly design revisions at later stages [50]. Schedule pressure (e.g., stemming from financing plans or procurement deadlines) often results in shortened investigation phases and omission of seasonal or long-term monitoring. In some cases, design decisions are made before the geological ground model has been fully developed [51]. Moreover, the client, the geotechnical investigation contractor, and the designer often operate independently, which hinders data integration and comprehensive interpretation. The lack of unified geological risk management in creases the risk of systemic errors [52]. In karst or geologically complex areas, conventional point-drilling methods are often insufficient. Where complementary techniques (ERT, AMT, GPR) are not employed, the resulting geological model carries significant uncertainty. Additionally, the lack of standardization in data interpretation hinders comparability across projects [45; 53]. Effective risk management requires not only more extensive geological data, but also a structured approach to their assessment, including hazard prioritization and the selection of mitigation strategies based on potential consequences [54]. It is also important to emphasize the potential cost increases resulting from the identification of unforeseen ground conditions. Geotechnical problems in projects are a key driver of claims, contract modifications, as well as budget and schedule overruns [55]. As demonstrated in analyses of hydrotechnical projects in China (Guangxi, a karst province), among 644 reservoirs requiring leakage repairs, the average cost of reconstructing seepage control systems significantly increased the total construction costs [44]. Similarly, in the case of the Montejaque reservoir (Spain), the loss of functionality due to unforeseen karst voids led to the complete failure of the investment, as the reservoir was never filled [43]. A World Bank report indicates that the average cost overrun in hydroelectric projects can reach 27%, with schedules extended by approximately 28%, which is correlated with insufficient geotechnical investigation [56]. Experience from Australian dams shows a median cost overrun of 49%, and an average as high as 120%, largely due to unforeseen ground conditions [49]. The most recent meta-analyses of dam projects completed after 2000 support these observations, reporting an average cost increase of 33% and a schedule delay of 18% [57]. Optimization of geological investigations (both geotechnical and geophysical) at the investment planning stage brings significant economic and technical benefits. Well-designed subsurface investigations reduce uncertainty regarding ground and groundwater conditions, which translates into lower risk of costly design modifications, delays, and failures during construction and operation. The financial benefits of thorough geological investigations far outweigh their costs, as reliable geotechnical data enable the design of safer and more economical foundations, while expenditures on investigations usually represent only a small fraction of the total investment budget [58]. According to the Geotechnical Engineering Committee of the U.S. National Research Council (NRC), as early as the 1980s it was recommended to allocate at least 3% of the total project cost to comprehensive geological-engineering investigations (particularly for underground works, tunnels, and dams), which remains economically justified given the potential consequences of inadequate investigations [59]. More recent studies have proposed probabilistic frameworks for cost-benefit analysis (CBA) of geotechnical investigations, taking into account the uncertainty of ground parameters and the influence of investigation scope on the total project cost.