Abstract: Accurate assessment of the saturated uniaxial compressive strength (Rc) of moderately weathered rock and slightly weathered rock is crucial for geotechnical engineering design and safety evaluation. However, the statistical deviations and variations in failure probabilities resulting from merging the Rc statistics of moderately and slightly weathered rocks remain unclear. This study aims to conduct a statistical analysis of Rc for moderately weathered rock and slightly weathered rock through an engineering case study in Guangzhou, evaluating the impact of merging statistics on data distribution characteristics and failure probabilities. This study separately analyzes the Rc data of moderately and slightly weathered rocks, calculating conventional statistics (e.g., mean, standard deviation, etc.). Subsequently, the Rc data of the two rock types were merged to calculate conventional statistics and estimate the central tendency range, degree of dispersion, density function, and failure probabilities of the data. By comparing the results of stratified statistical analysis and merged statistical analysis, the impact of Merging Statistics on data distribution characteristics and failure probabilities was analyzed. The results indicate that the representativeness of conventional statistical measures significantly decreases after merging statistical analysis. The merged Rc data distribution deviates from fundamental statistical assumptions, leading to a substantial increase in failure probabilities. Merged statistical analysis is not conservative and may underestimate engineering risks. The proposed methodology demonstrates strong practicality and represents the first proposal in the field of engineering investigation, possessing certain value for promotion and application.