1.Introduction 1.3 Design Principle Principle 2 Selection of an optimum support system,including support type, installation procedure and time,strength and stiffness Principle 2.1 Ring closure needed for support mobilisation Principle 2.2 Intimate contact between ground and support Principle 2.3 Inner support ring has to behave as a thin-walled shell,maximising normal stresses and minimising moments(avoiding internal shear) Principle 2.4 Support capacity increasing has to be done by reinforcement(steel sets,anchors etc.)rather than by cross-section thickening 百年同 *6 6 Principle 2 Selection of an optimum support system, including support type, installation procedure and time, strength and stiffness Principle 2.1 Ring closure needed for support mobilisation Principle 2.2 Intimate contact between ground and support Principle 2.3 Inner support ring has to behave as a thin-walled shell, maximising normal stresses and minimising moments (avoiding internal shear) Principle 2.4 Support capacity increasing has to be done by reinforcement (steel sets, anchors etc.) rather than by cross-section thickening 1. Introduction 1.3 Design Principle