首先探讨了围岩自承能力的力学机制，认为围岩自承能力来源于强度，围岩塑性强化区和弹性区是主要的承载结构。新奥法“充分发挥围岩自承能力”的观点可进一步表述为“基本维持围岩原始状态”，这是一种“显性”表述，提出了技术方向，具有可操作性。将能量最小原理分别应用于石质隧道和土质、破碎围岩隧道，对其具体含意进行了深入阐述，提出此原理可以作为判断各种施工方案优劣的依据。

The mechanisms for the selfsupport ability of the surrounding rock mass are discussed. Conclusion is drawn that the selfsupport ability of the surrounding rock mass originates from the strength of the surrounding rock mass and that the plasticallystrengthened zones and the elastic zones of the surrounding rock mass are the major loadbearing structures. NATM’s viewpoint that the selfsupport ability of the surrounding rock mass should be fully exerted can be further described as that the initial state of the surrounding rock mass should be basically maintained, which is an explicit expresstion. This conclusion provides a technological direction and has certain operationability. The minimumenergy principle is applied in rock tunnels, soil tunnels and tunnels located in fractured ground respectively. The meaning of the minimumenergy principle is expounded thoroughly. It is stated that the minimumenergy principle can be used as one of the criteria to determine whether each construction plan is good or not.