Assessment of rock drillability by the method of analytic hierarchy process combined with fuzzy comprehensive evaluation

Comprehensively and reliably assessing the rock drillability is a vital prerequisite for guiding the rapid construction of pile foundation engineering. This paper studies rock drillability and its evaluation method. We established a grading standard of influencing factors by analyzing the factors that influence drilling, according to the physical–mechanical properties of rock and actual drilling characteristics. Based on the hierarchy of these factors, a two-layer fuzzy comprehensive evaluation model is proposed. The analytic hierarchy process (AHP) is used to determine the weight of each stage factor, the fuzzy sets method is used to determine the membership function, and the influencing factors are ranked. This model was applied to the construction of the 2nd Humen Bridge Project. The results show that the physical properties of rock have the greatest impact on drillability, and the weight is 0.443. The content of quartz and iron in the physical properties is the prime factor affecting the rock drillability. The results of assessment and calculation are in line with the site conditions, which validate the feasibility and practicability of the fuzzy comprehensive evaluation (FCE) method for the rock drillability established in this paper. This study can also serve as guidelines for other rock-drilling engineering.