In this paper, the author points out several key problems needed to be solved about the dynamics of frozen soil by reviewing related literatures about hysteretic curve of frozen soil ,dynamic constitutive relation and dynamical parameter. The problems are the insufficient understanding on morphological characteristics of hysteretic curve and how to transform qualitative understanding into quantitative understanding about morphological characteristics of hysteretic curve. The problem is the rationality of selecting the dynamic constitutive model, namely how to establish the engineering applicable model which conforms to the actual soil mechanics performance.The problem is the rationality of the calculation method about dynamic elastic modulus and damping ratio, namely how to define dynamic modulus of elasticity of frozen soil correctly and the limitation of using the classical method to calculate the damping.

Based on MTS-810 type vibration testing machine, morphological characteristics of hysteretic curves of frozen clay are quantitatively studied, and dynamic mechanical response are analyzed consisting of stiffness, viscosity, degree of microscopic damage, residual strain and energy dissipation. The studies have shown that the higher vibration frequencies are, the greater the stiffness is, while the smaller viscosity, the degree of microscopic damage, residual strain and energy dissipation are. Stiffness, viscosity, degree of microscopic damage, residual strain and energy dissipation are less affected by confining pressure. With increasing dynamic stress amplitude, stiffness decreases gradually, while viscosity, degree of microscopic damage, residual strain and energy dissipation increase gradually.

Combined with the current research situation of construction of tunnels with small clear spacing, the key technology of design and construction of tunnels with small clear spacing is summarized, which primarily consists of rational clear interval of tunnels with small clear spacing, advanced support, construction methods and clip rock reinforcement. The passage describes various methods of key technologies currently in use and the selecting rule under the condition of various categories of surrounding rocks, which has some significance on the safe construction of tunnels with small clear spacing.

Under the effect of periodic cycle load, the frozen soil exists hysteretic characteristics. According to the research, the five parameters which are the residual strain , the numerical of short axis to long axis of the hysteretic curve , the slope of the hysteretic curve long axis k, the distance of adjacent hysteretic curve center point d and the area surrounded by hysteretic curve S are used to quantitatively represent the morphological characteristics of the hysteretic curve. The hysteretic curve of frozen soil is not a standard ellipse. Its morphological characteristics relate to the initial loading position. The morphological characteristics of the hysteretic curve of different soil affected by frequency, confining pressure and dynamic stress amplitude are different.