It is the foundation of tunnel engineering to classify the rock mass surrounding tunnels. However, it is not easy to precisely determine the class of rock mass in practice as sufficient geological exploration need to be completed before rock mass classification, and there exists some disputes referring to the rationalization of dozens of methods for rock mass classification through the world. The principles and procedures of the basic quality method, which are widely used in China, are presented in this paper, and the application process of the basic quality method is showed with a project case of Zhongnanshan highway tunnel which has operated in safety for nearly a decade. Then, both the advantages and disadvantages of the basic quality method are analyzed in terms of practical engineering applications. In consideration of the defects of the basic quality method, the concept of the subclassing of surrounding rock in grade III–V is developed in the end and the criterion is given to determine the subclass of rock mass. This study is aimed at providing some useful ideas and a reference for rock classification in highway tunnel engineering.

Aiming at the problems of the negative sequence governance and regenerative braking energy utilization of electrified railways, a layered compensation optimization strategy considering the power flow of energy storage systems was proposed based on the railway power conditioner. The paper introduces the topology of the energy storage type railway power conditioner, and analyzes its negative sequence compensation and regenerative braking energy utilization mechanism. Considering the influence of equipment capacity and power flow of the energy storage system on railway power conditioner compensation effect, the objective function and constraint conditions of the layered compensation optimization of the energy storage type railway power conditioner were constructed, and the sequential quadratic programming method was used to solve the problem. The feasibility of the proposed strategy is verified by a multi-condition simulation test. The results show that the proposed optimization compensation strategy can realize negative sequence compensation and regenerative braking energy utilization, improve the power factor of traction substations when the system equipment capacity is limited, and it also has good real-time performance.