Experimental Study On Stiffness And Damping Ratio Of Frozen-thawed Soil Under Subway Loading

Freezing technology is frequently used in the subway interconnecting roads and the departure and reception parts,which is realized through the circulation of cooling liquid.It makes the soil cold and freeze to meet the needs of soil strength and anti-permeability.But this technology also makes the ground suffer from freezing swell and melting settlement.Dynamic stiffness and damping are changed,and the frozen-thawed area becomes a weak part of the underground.Therefore,it's necessary to study the dynamic stiffness and damp of frozen-thawed soil under metro loading.This paper is about simulating metro loading by dynamic triaxial test,thus obtaining data of hysteretic curves?dynamic stiffness and damping ratio of the freeze-thawed soil.To study the affection of freezing and consolidation,a new function is created to imitate the softening of stiffness,so it is possible to analyze the effect freezing temperature and degree of consolidation have on the stiffness and the damping ratio of the soil.And different ways to calculate damping ratio are compared.Main ideas are simplified as following:(1)The development of hysteretic curves has stages and self-similarity under cyclic loading.The shape of the hysteretic curves depends on the lagging of strain to stress,and can be classified as oval?moon and willow leaf etc.Damping force and plastic deformation both have influence on the change of curve,and it can be found by the phase delay between strain and stress.(2)Apiecewise function is used to describe the two stages of stiffness softening,turning point appears at 3000 to 8000.A few parameters being defined in the function prove that the effect of freeze-thaw increases the degree and speed of stiffness softening(3)Several ways to calculate damping ratio are compared,and one of them is proved much more feasible.Damping change has two stages too,and damping ratio decreases faster than stiffness.(4)When the stress amplitude is invariant,damping ratio depends on stiffness and the area of hysteresis curve,they have a direct ratio relation.The development of damping is also affected by degree of consolidation and freezing temperature,but in a complicated way.At about-10? damping ratio has a minimum value.Consolidating effect decreases the initial damping ratio,but also makes the loss ratio of daming lower after the loading process.