Dissecting the Robustness of the Rock Mass Classification Methods Used in Jiaozhou Bay Subsea Tunnel

Abstract

To confirm the robustness of a tunnel, the quality of the rock mass is usually evaluated by several rock mass classification (RMC) systems before its design. Besides, the accuracy of the RMC should be checked through the correlations between different RMC systems. The relationship between the different RMC systems and P-wave velocity indexes is conducive to the interpretation of the rock mass. Here, based on linear or nonlinear regression analysis of 231 samples, we established the RMR–Q, [BQ]–Q, and [BQ]–RMR relationships with R2 = 0.935, 0.732, and 0.759, respectively. Further analysis showed that the grading differences between any two RMC systems yield different characteristics when the rock mass score is at different intervals. To evaluate the relations between RMC indexes and P-wave velocity, we conducted a group study on the different grading differences among RMR, Q, or BQ. Depending on the consistency of the grading results, we arranged the values from large to small as the amplitude of the slope of the curve, and the grading results differed by either one or two levels. Our data demonstrated that the grading differences between the systems are proportional to the discontinuous state of rock mass in the classification. In addition, the classification results of Q, RMR, and BQ showed more significant differences when less consideration is given to the integrity of the rock mass.