ESSENTIAL ISSUES AND THEIR RESEARCH PROGRESS IN TUNNEL AND UNDERGROUND ENGINEERING

As three essential issues in tunnel and underground engineering contain stability of surrounding rocks, interact relation between support and surrounding rock as well as structural dynamic response of a support system are also the key problems in subject study.All around these issues, this paper emphatically analyzes the surrounding rock mechanical characteristics and load effect, and establishes mechanical model of internal and external surrounding rock.Based on the study of stability of structure layer in model above, analytic formula of ground reaction curve and computing method of surrounding rock load effect are given.According to the analysis of interact relation between support and surrounding rock, this interactional dynamic process is divided into four stages:free ground deforming, advance supporting, preliminary supporting, secondary supporting, thus description method of the dynamic process is raised.On idea of generalized load and special load, basic functions of support: "mobilizing" and "assisting" are proposed, then their implementations are clarified, which are"mobilizing" surrounding rock to bear the load reinforcement by applying surrounding rock reinforcement, advance reinforcement and bolt support, "assisting"surrounding rock to bear the load by using the supporting structure.Aiming at the complex tunnel support system, the concept of dynamic optimization of multi-objective and staged synergistic effect is put forward, which can realize the coordination of various supporting structures in terms of time and space to improve the reliability.In view of the safety characteristics of extremely unstable complex surrounding rock, the safety accident mechanism model of three patterns is established.A new concept of safety classification is put forward based on the characteristics of engineering response, and a gradation index system and classification method are established.On account of the underwater tunnel and water-enriched surrounding rock, three patterns of water inrush mechanism model are established, and the theory and method of safety control based on deformation control of surrounding rock are put forward.At last, the hotspot and core problems of the discipline development are analyzed and prospected.