Research On Dynamic Characteristics Of New Liquid Fly Ash In Seasonal Freezing Region

The three provinces of northeast China are typical seasonal frozen soil regions in China.Due to the influence of climate,the roadbed in this region has been subjected to the alternating effect of freezing in winter and ablation in spring for a long time,resulting in the continuous decrease of the strength of roadbed soil.In addition,the long-term dynamic load of vehicles weakens the stability of subgrade soil and water,resulting in uneven settlement,which leads to the emergence of slurry,mud and other diseases on the road surface,which will not only endanger driving safety,but also affect the foundation stability of the structures on both sides of the road.In order to solve this kind of engineering problems,the researchers systematically studied all kinds of new roadbed fillings from the perspective of improving roadbed fillings’ performance.Among many research objects,the newly mixed liquid fly ash,which is made of cement,lime,fly ash and water in a certain proportion,has strong frost resistance,good water stability,high strength in the later stage and excellent road performance.It can effectively solve the above engineering problems and is very suitable for road construction in seasonal freezing areas in China.However,there is no research on the dynamic characteristics of the newly mixed liquid fly ash,so it is necessary to systematically study the dynamic characteristics of the fly ash through indoor dynamic triaxial test,so as to provide a theoretical basis for its large-scale engineering application in China’s seasonal freezing region.This paper takes the newly mixed liquid fly ash as the research object,systematically studies the dynamic characteristics parameters and their variation rules of dynamic strength,dynamic shear modulus and damping ratio under the action of freezing-thawing cycle,and makes a fitting analysis of the relationship between dynamic shear modulus and damping ratio and its influencing factors,and draws the following conclusions:(1)The dynamic strength index of freshly mixed liquid fly ash is approximately linear with the change of vibration number N in logarithmic coordinate,and decreases with the increase of vibration number.The relationship between dynamic shear stress and vibration number N can be well fitted,and the dynamic shear strength parameters obtained by Mohr--Coulomb strength theory and the variation law affected by various factors are completely consistent with the dynamic strength.(2)The dynamic strength of freshly mixed liquid fly ash increases with the increase of confining pressure and decreases with the increase of the number and frequency of freeze-thaw cycles.Before the freeze-thaw cycle,the maximum dynamic strength corresponding to the mix ratio of 6:8:86,8:4:88 and 8:8:84 was 154kPa,174kPa and 164kPa,respectively.After eight freeze-thaw cycles,the maximum dynamic strength was 123kPa,138kPa and 130kPa,respectively.When the number of freeze-thaw cycles is more than 8 times,the dynamic strength of each mix tends to be stable.(3)The axial cumulative strain of fresh liquid fly ash can be divided into stable,destructive and critical types according to the development situation.Under the condition of constant dynamic stress ratio,the strain form of the sample with the mixing ratio 6:8:86 would be critical type,and the strain variables of the mixing ratio 8:4:88 and 8:8:84 almost did not change,and they all showed stable type,but 8:4:88 was more stable.Therefore,the mixture ratio of 8:4:88 is more suitable for practical road engineering applications.(4)The hardin-Drnevich hyperbolic model can better describe the dynamic stress-strain relationship of fresh liquid fly ash,so the model can be used to calculate the specific values of maximum dynamic shear modulus and maximum damping ratio.Then,the prediction models under the influence of confining pressure and the number of freezing-thawing cycles were established by regression analysis,as shown below:(?)In practical engineering,under the condition of known confining pressure and freezing-thawing cycles,the operation process of moving triaxial test can be avoided,and the prediction of maximum dynamic shear modulus and maximum damping ratio can be realized directly by using this model,which has certain reference value for the application of fresh liquid fly ash in seasonal freezing region.(5)The dynamic shear modulus decreases with the increase of freezing-thawing cycles,and increases with the increase of confining pressure and vibration frequency,while the damping ratio is opposite.Before freeze-thaw cycles,the maximum dynamic shear moduli corresponding to 6:8:86,8:4:88 and 8:8:84 samples were 36.2mpa,41.5mpa and 37.6mpa,respectively.After eight freeze-thaw cycles,the maximum dynamic shear moduli were 28.6mpa,33.1mpa and 28.7mpa,respectively.When the number of freeze-thaw cycles is more than 8,the dynamic shear modulus of each mixture tends to be stable.