| Freeze-thaw action causes soil moisture migration and changes soil structure,which results in a series of physical changes.Modulus of resilience is an important parameter to evaluate the mechanical performance of subgrade.At present,the test methods of modulus of resilience of subgrade mainly include field bearing plate method,Beckmann beam deflection method and FWD method,which are time-consuming and laborious.The dynamic modulus of subgrade is used instead of the static modulus of subgrade in the current Code of China,but the test of dynamic modulus of subgrade soil is still complicated,therefore,an easy-to-obtain physical parameter is used to obtain the dynamic resilient modulus of subgrade soil.In this paper,the shear wave velocity is used to characterize the dynamic resilient modulus of subgrade soil,and the characteristics of shear wave velocity and dynamic resilient modulus of silty clay under different working conditions are discussed,a simple and convenient method is provided for the prediction of subgrade soil modulus.The main research contents and findings are as follows:Firstly,an indoor one-dimensional freeze-thaw cycle test system was set up by using a thermoelectric semiconductor chip,an integrated temperature control system and a data acquisition system,the shear wave velocity measurement system is established by using wave generator,filter,oscilloscope and localizer.On this basis,a one-dimensional unidirectional freezing-thawing cycle-shear wave velocity measurement system for subgrade soil is developed.Secondly,based on the test of shear wave velocity,the influence of water content,compactness,saturation and freezing-thawing times on the shear wave velocity of subgrade soil is studied,and the evolution law of anisotropy of subgrade soil with saturation and freezing-thawing times is studied,the mechanism of freeze-thaw cycle is revealed.It is found that the increase of water content and freeze-thaw cycles leads to the decrease of shear wave velocity and the increase of anisotropy index;The shear wave velocity increases with the increase of saturation below the critical saturation and vice versa.On this basis,the prediction formula of shear wave velocity is established with the parameters of saturation degree and freeze-thaw times.Finally,the dynamic modulus of subgrade soil was tested by dynamic servo hydraulic material testing machine,and the effects of different compaction degree,moisture content,stress state and freezing-thawing times on dynamic modulus of subgrade soil were studied.It is found that the increase of compaction degree,confining pressure and deviating stress will lead to the significant increase of dynamic resilient modulus of subgrade soil,while the increase of moisture content and the number of freeze-thaw cycles will lead to the decrease of dynamic resilient modulus of subgrade soil,considering the influence of degree of compaction,water content and freezing-thawing times on dynamic modulus of subgrade soil,a formula for predicting dynamic modulus of subgrade soil is established.According to the measured values of shear wave velocity and dynamic resilient modulus,the direct conversion relationship between them is obtained,the conversion relationship between wave velocity and modulus is established with the parameters of saturation and freezing-thawing times. |
