Studies On Characterizing Of The Relaxation Modulus Of Frozen Soil Based On The Spherical Template Indenter And Its Adaptability

Cold regions engineering exploration,design,construction and so on need a better understanding of the creep properties of frozen soils.The related studies can predict the changing regularity of long-term strength and the creep deformations of frozen soils precisely.It can effectively mitigate engineering hazards resulting from the frozen soils creeping deformations.With many unique advantages compared with other static loading tests,the spherical template indenter test can be applied as a powerful way to determine the creep property of frozen soil.However,most recent studies have concentrated on changes in the long-term strength of frozen soils.Thus,based on the indenter test,this paper studies the characterizing method of frozen soil relaxation modulus,parameters identification principal of visco-elastic contact model and the changing regularity of frozen soil contact stress and deformation.It conducts basic physical property test spherical template indenter test and ultrasonic test and so on of frozen sand.This work can be used as the reference for improving the characterization method of frozen soil relaxation modulus,understanding the contact behavior of frozen soil and examination whether a viscoelastic contact model has a unique solution of parameters or not through the reverse analysis process.Project scopes and major conclusions are as follows:Firstly,the characterization method of relaxation moduli of frozen-soils is built for the dead and dynamic loading creeps and relaxation tests.Besides,the parameters identification principle of fraction order viscoelastic model(FOVEM)and solution of fraction order Kelvin model are deduced.It proves that arbitrary one kind of these three tests is needed for determining both relaxation modulus and creep compliance function.Based on FOVEM,if all the mechanics' parameters are unknown,it has no unique solution through the reverse analysis of the test curves.Besides,even the value of the Poisson ratio is given,the solution for the parameters are nonunique when more than two fraction-order Maxwell or Spring units cascading with Kelvin units;To extract the unique solution of material parameters,the Kelvin units should have unique time scales or fraction orders indexes if more than two Kelvin units cascade with each other.If thevalue of the Poisson ratio was given,the fraction-order Kelvin models would have unique solutions for material parameters through the back-analysis.Secondly,based on the solutions of the fraction-order Kelvin model(FOKM),the frozen-soil relaxation modulus through the dead spherical template indenter tests of frozen sand are compared and contrasted with those by other static and dynamic loading tests.Besides,the results of the spherical indentation relaxation and cone indentation creep tests of PMMA(Polymethyl methacrylate)and the cone indentation relaxation and creep tests of PC materials(Polycarbonate)are also compared and contrasted with those by uni-axial creep tests respectively.Additionally,the results of uniaxial creep tests of frozen clayey soils are analyzed.It shows that frozen soil relaxation modulus predicted by FOKM agrees well with that by the Roman solution,which is smaller than those by other static and dynamic loading tests.Therefore,the predicted value of frozen soil relaxation modulus based on FOKM is more conservative.The predicted relaxation moduli of PMMA materials by FOKM is closer to those of the earlier uni-axial creep tests.However,the variability of time series of relaxation modulus and creep compliance of PC material is inconsistent with those of uni-axial creep tests.This may be related to the lack of the modules for descriptions of the elastic transient shear deformations in FOKM and the high concentration of stress at the tip of the conical indenter.Besides,its predicted results on the variability of relaxation moduli of frozen clayey soils with soil temperature and stress have well confirmed existing research conclusions.Thirdly,Simulations with the finite element method for the dead-load creep test well predicts bump deformation at an indenter edge,consistent with the phenomenon recorded during the test.The compression stress decreases with increasing radial distance,which is similar to the predictions by Hertz contact theory.In contrast,the shear stress at the contacting surface increases with increasing radial distance.The simulation also provides a high value of compression stress(more than 10MPa)at the initial contacting,giving a reason why ice crystal thaws and weakening of the frozen-soil structure at the contacting area.This also explains the cause of why the relaxation modulus has a sharp reduction at the initial stage.With increasing compression deformation,the distribution of compression stress becomes smooth anduniform,resulting in a lower decreasing rate of relaxation modulus versus time.