| As the key structure that bears and transmits traffic loading to the soil,road base is subjected to massive cyclic loading during its service period.Therefore,a deep understanding of the development of stiffness and accumulated strain of road base under long-term traffic loading is the premise to assure the long-term road service performance.Unbound Granular Materials(UGMs)are widely used as road base fillings for its well mechanical and drainage properties.Nowadays,the scholars have made a series of researches on the dynamic behaviors of UGMs under traffic loading.The effects of different factors such as the physical states of UGMs and the loading amplitude on the resilient and accumulated strains of UGMs have been investigated.While under the tendency of fast development of intensive and high speed transportation,as a result,the influence of cyclic loading frequency on the long-term dynamic behaviors of UGMs can't be ignored.Besides,the invasion of the fine particles from the subgrade caused by mud pumping will influence the strength and deformation properties of the road base fillings.The fines will change particle size distribution,permeability of UGMs and the interaction between grain networks,which will affect the long-term service performation.Therefore,in order toreveal the effects of the loading frequency and fines content on the long-term dynamic behaviors of UGMs,it's necessary to carry out researches on the dynamic behaviors of UGMs with different fines contents under typical loading frequencies,and analyze the properties of UGMs under different degree of fines pollution.In this study,in order to investigate long-term dynamic properties of crushed tuff with different fines contents under cyclic loading with different frequencies,a series of cyclic large-scale triaxial tests have been conducted with GDS large-scale cyclic triaxial apparatus,the main research contents are listed as follows:1.In order to investigate the effects of loading frequency,a series of cyclic large-scale triaxial tests on the UGMs under saturated drained condition have been conducted with GDS large-scale cyclic triaxial apparatus.The influence of loading frequency and stress path on the long-term performance of UGMs are investigated systematically,and obtain the influence of loading frequency on the development of resilient modulus,volumetric strain and accumulated axial strain.The experimental results show that loadings with higher frequency results in a larger accumulated volume contraction during the stage of densification,and consequently the UGMs reach a higher resilient modulus value.The accumulated axial strains of UGMs are also different under loadings with different frequencies.At the stage of densification of UGMs,loadings with higher frequency leads to higher accumulated axial strain when cyclic stress ratios are high,while the loading frequency's influence is minimized when the cyclic stress ratio is low.After the UGMs reach the stable deformation stage,loading frequency almost has no influence on the accumulated axial strain.Therefore,the effects of loading frequency on the long-term performance of road base can be significantly reduced by controlling the cyclic stress ratio in the UGMs to a low level.2.Combined with test data of accumulated axial strain under different loading frequency,the High-cycle Accumulation Model which predicts the accumulated strain of UGMs under large numbers of cyclic loading is modified.With the introduction of a new impact factor ff,a new model that considers the influence of the loading frequency is developed which can predict the settlement of road base based on HCA Model.The study shows that this model can predict the settlment of road base accurately under loading with different frequencies corresponding to typical loading frequencies.It provides an effecive tool to predict and control the post-construction settlement of road more comprehensively.3.In order to investigate the dynamic behaviors of road base with different degree of fines pollution under the traffic loading,a series of large-scale triaxial tests have been conducted on crushed tuff.Pollution road base filling materials are simulated by mixed with different magnitudes of fines contents.Large-scale triaxial cyclic loading tests are carried out on the road base with 5 magnitudes of fines contents subjected to 3 loading frequencies to consider the coupling effects of fines content and loading frequency,and focus on the development of excess pore pressure,volumetric strain,resilient modulus and accumulated axial strain.The studied results show that the effects of fines content of UGMs can be divided into three stages.Firstly,under low fines content condition,the fine particles can lubricate the contact of the UGMs which can increase the volumetric strain and accumulated axial strain;with the increase of fine particles,the voids of the UGMs are filled with the fine particles which makes the compressibility of the UGMs decrease,and consequently decreases the stains;when the fines content increases to a certain value,the permeability of the UGMs becomes low which makes the buidup of excess pore pressure.In this case,the axial strain increases significantly and the the resilient modulus decreases sharply.Moreover,the influence level of the fines contents on the UGMs' long-term behaviors is highly influenced by loading frequency.In addition,high loading frequency will aggravate the excess pore pressure which makes the pavement's long-term service ability degraded. |
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