Dynamic Response Characteristics Of Soft Subgrade Covering Dry Crust Under Vehicle Load

Taking advantage of dry crust’s shell effectis significant to road engineering. The study on the dry crust is more concentrated on the statics scope.With the emergence of high-speed、overweight vehicle, it’s important to research thedynamic properties of subgrade under vehicle load.First of all,the Numerical model of soft subgrade covering dry crust under vehicle loadisset up by finite difference software FLAC3 Dtostudy the dynamitic stress wave propagationin hard and soft soil.Effects of the property of dry crustand vehicle speed on dynamic stress diffusion areanalyzed,and it comes to a conclusion of pilot study.Based on the stress wave theory,in respect of obvious wave impedance difference between dry crust and soft underlayer,the phenomenon of dynamical stress mutation at hard-soft soil contact surface is revealed by transmission coefficient.The attenuation law of vertical dynamic stress peak in subgrade soil under vehicle load is obtained by numerical simulation.A transfer coefficient at soil layer interface is deduced, which can represent the law of dynamical stress mutation synthetically, on the basis of attenuation curve’s negative exponential function characteristic.The corresponding calculation method and application sphere of transfer coefficient is offered, which is of process simplicity and high precision compared with the existing methods via monitoring data verification.An indoor model testis carried outof soft subgrade covering dry crust under vehicle load.Cement soilis used to study the characteristics of the dry crust. Orthogonality method is adopted to make the trial planto verifie the effect of different factors on the properties of stress dispersion of dry crustfrom the perspective of experiment.The influence degrees of the dry crust thickness, hardness and vehicle weight, vehicle speedare analyzed.The mechanism of action of the dry crust is also obtained.The energy absorption coefficient ? is calculated inversely, which is negative exponential function relationship with model scale k base on data fitting results, after the dynamic stress attenuation law is obtained using numerical simulation technique. Then the mathematical formula is built, which can reveal the size effect law in homogeneous soils. The equation of size effect is derived to uncover the response law at transition section of soil layer interface, whose characterization parameter is soil layer interface’s energy absorption coefficient ?, and the numerical range of undetermined coefficients is provided.