After noticing poor rock penetration performance during pile excavation works, contractor induced additional site investigation to support his claim on higher rock strength than previously inspected. Results of 115 point load tests and 97 uniaxial tests were fitted to Weibull and Gamma probability density functions. One-sided confidence interval with confidence level of 95% (CI95) for strength value which is higher than 95% of population (i.e. 95% percentile) was obtained with "Likelihood Ratio Confidence Bounds" method. Suggestion on number of specimens is given for percentile interval estimation in future geotechnical investigation works.

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