| EPS particles light weight soil is a new type of geo-material,which uses EPS(expanded polystyrene)particles to reduce soil weight and cement solidifying agent to enhance the strength of soil.Polystyrene foam particles make rational use of the most difficult white material.Light weight soil has the advantages of light weight,compression resistance,earthquake resistance,durability,self-reliance and heat insulation.It plays an important and irreplaceable role in the conditions of uneven settlement of soft soil ground,transformation of steep slopes in mountainous areas,vehicle jumping at bridgehead,bay filling,pipeline engineering,etc.With the continuous development of road engineering,the road is often damaged under the action of traffic load,so the quantitative dynamic deformation analysis of light weight soil roadbed has become an urgent problem to be solved.At present,the commonly used method is to establish the dynamic constitutive model of soil,and analyze the dynamic shear modulus,damping ratio,dynamic shear stress and dynamic shear strain under different stress conditions.Therefore,based on the test results of indoor dynamic triaxial test and unconfined compression test,the dynamic deformation characteristics of light weight soil and the applicability of three viscoelastic dynamic constitutive models are discussed systematically.The results are as follows:(1)The dynamic triaxial tests of light weight soil was carried out to explore the influence of different material proportion,confining pressure and frequency on the backbone curves,dynamic shear modulus and damping ratio of light weight soil,and the dynamic triaxial tests of remoulded soil was set as the control tests.The backbone curves of light weight soil show obvious nonlinear characteristics.With the increasing of confining pressure and frequency,the dynamic shear modulus increases at the same strain level,while the damping ratio decreases.The damping ratio curves of light weight soil shows a special “bell shaped” non-linear change law when the volume ratio of EPS particles is less than 40% and the cement content is more than 10%.In other conditions,the damping ratio curves of light weight soil follows the “Sshaped” change law of conventional soil.Based on the test results,the Hardin empirical formula of conventional soil is improved,and the structural parameters are introduced to characterize the change of light weight soil ratio.The empirical formula suitable for describing the maximum dynamic shear modulus and maximum damping ratio of EPS particles light weight soil is obtained.(2)Based on Hardin-Drnevich model,the dynamic triaxial test results of light weight soil are analyzed,and the influence rules of different proportion and confining pressure on the backbone curves and model parameters of light weight soil are explored.With the increasing of confining pressure,the initial slope of dynamic shear stress-strain curves of light weight soil increases significantly.The dynamic deformation characteristics of light weight soil under dynamic load can be described by Hardin-Drnevich model.Based on the empirical formula of Hardin-Black maximum dynamic shear modulus and previous studies,the structural parameters k of light weight soil is introduced,and the coupling contradiction between EPS particles and cement is solved by using void ratio e.The expressions of Hardin-Drnevich model parameters suitable for describing different proportion and stress conditions of light weight soil are established,which can determine the parameters under different proportion and stress conditions.By changing the stress state to carry out the verification tests,the calculated values of the model can predict the test scatter well,which shows that Hardin-Drnevich model and parameter empirical expressions can be used to describe the backbone curves of light weight soil.(3)Combined with the Ramberg-Osgood model with variable parameters,the parameters of the dynamic triaxial test results of light weight soil are extracted,and the change laws and applicable ranges of the model parameters with the dynamic shear strain of light weight soil are obtained.The influence of EPS particle content,cement content ratio and confining pressure on the model parameters is analyzed.With the increasing of EPS particle content,the stable values of parameter R increases gradually,while with the increasing of confining pressure.The damping effect of light weight soil will show two different curve forms of “bellshape” and “S-shape”.The Ramberg-Osgood model with variable parameters can adjust the parameter value with the change of dynamic shear strain,so it can well describe the dynamic shear modulus ratio and damping ratio change laws of light weight soil after changing the dynamic state.(4)Based on the Davidenkov constitutive model,the nonlinear regressions of the dynamic triaxial test results of light weight soil are carried out.The influence of EPS content,cement content and confining pressure on the model parameters is analyzed.The ranges of parameters of Davidenkov model are obtained.The influence of confining pressure on the dynamic shear modulus ratio curve is significant with the increasing of EPS content and cement content.The shape of dynamic shear modulus ratio curves of light weight soil is affected by three parameters of Davidenkov model.The damping ratio of light weight soil under dynamic load changes with dynamic shear stress in two forms of “bell-shape” and “S-shape”.The modified formula of damping ratio of light weight soil can describe the change laws of scattered point in “S-shape” test of light weight soil,but it is difficult to predict the curves of damping ratio of light weight soil.The verification test shows that the calculation values of Davidenkov model can predict the triaxial test values of light weight soil well by changing the stress state and the conventional stress loading path.When the dynamic load span is large or the dynamic load is loaded or unloaded,the prediction values of Davidenkov model are small. |
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