| Coarse-grained soil materials are widely used in subgrade filling projects due to their good mechanical performance and excellent water permeability.As the key structure for transmitting traffic load,road subgrade plays an important role in the long-term service of the road.With the current traffic load presenting the trend of high speed,heavy load and high flow,it is particularly important to accurately grasp the dynamic response law of roadbed materials under long-term traffic load and predict its settlement deformation.Coarse-grained soil is widely distributed in nature,and the grain gradation of coarse-grained soil is different in different areas.In the same area,the weathering effect gradually weakens with increasing depth,and the content of block stones gradually increases.In addition,during the service period of the roadbed filler,the heavy load of the vehicle causes the coarse-grained soil to break,and the effect of rainfall infiltration hydraulic slope drop will cause the change of the roadbed filler's coarse-grained content.These changes will inevitably affect the internal performance and gradation of the coarse-grained soil filler,which in turn will affect the strength,dynamic parameters and deformation characteristics of the roadbed filler under the long-term cyclic load of the roadbed.As an important parameter reflecting the coarse-grained content and gradation characteristics of coarse-grained soil,P5content can not be ignored for its long-term dynamic characteristics of roadbed coarse-grained soil filler In addition,the roadbed material not only bears a unidirectional cyclic load during service,but the passing vehicles will also cause changes in dynamic confining pressure.Therefore,it is urgently needed to study the dynamic characteristics of subgrade fillers with different P5contents based on the true stress level of subgrade fillers,and to analyze the characteristics of subgrade fillers with different P5 contents to reveal the influence of P5 content on the long-term dynamic performance of coarse-grained subgrade fillers.In this paper,a series of static,one-way dynamic and two-way dynamic triaxial tests are carried out based on the GDS large-scale coarse-grained soil dynamic and static triaxial test system.The results have the following aspects:1.Through particle analysis and large-scale compaction test of coarse-grained soil,the influence of P5 content on gradation parameters,maximum dry density and optimal water content was analyzed.Studies have shown that with the increase of P5 content,the soil sample non-uniformity coefficient and geometric mean particle size both increase and then decrease,the curvature coefficient changes with the coarse particle content is not obvious,the weighted average particle size gradually increases with the increase of P5 content.The maximum dry density of the soil material increases first and then decreases with the P5 content.When the P5 content is 70%,the maximum dry density reaches the maximum.2.To study the effect of P5 content on the shear strength parameters and stress-strain parameters of coarse-grained soil.The GDS static triaxial test system was used to carry out the static triaxial test on the roadbed coarse-grained soil filler under different P5 contents.Tests show that the internal friction angle ? increases first and then decreases as the content of P5 increases.The linear relationship between the internal friction angle cp and the diameter-diameter ratio in double logarithmic coordinates is good.The relationship between the two can be described by a power function;the tangent mode increases with the increase of confining pressure.Under the same confining pressure,the tangent modulus increases first and then decreases with the increase of P5 content.The modulus K increases first and then decreases with the increase of P5 content.Modulus index n is not obvious with the increase of P5 content.3.In order to study the influence of P5 content on the dynamic characteristics of roadbed fillers under road cyclic loading,a series of large-scale dynamic triaxial test studies were carried out on roadbed fillers with different P5 contents.The research shows that the dynamic elastic modulus of samples with different P5 content decreases with the increase of dynamic strain;when P5=10%-70%,increasing the P5 content can significantly increase the maximum dynamic elastic modulus of the sample.When the P5 content increases from 70%to 90%,the maximum dynamic elastic modulus decreases by 10.3%;the relationship curve between the damping ratio and the dynamic strain is S-shaped,that is,the damping ratio increases slowly with the dynamic strain first,and then rapidly increases and eventually stabilizes;As the content of P5 increases,the damping ratio decreases first and then increases.The inflection point is P5=70%.The axial cumulative strain growth rate gradually decreases with the vibration frequency.After the vibration frequency N=1000,the axial cumulative strain rate is at a low level.The axial cumulative strain of the sample only slightly increases in the late loading stage,and the dynamic response of the sample gradually tend to be elastic.The final axial cumulative strain of the specimen decreases first and then increases with the increase of P5 content.Taking the fourth-level load as an example,when the P5 content increases from 10%to 70%,the cumulative axial strain decreases by 67.8%;when the P5 content increases from 70%to 90%,the cumulative axial strain increases by 111.5%.4.Moving traffic loads will also cause cyclically changing dynamic lateral stresses.In order to study the coupling effect of dynamic confining pressure and P5 content on coarse-grained soil subgrade fillers,a series of large-scale two-way dynamic triaxial tests were carried out on subgrade fillers with different P5 contents.The research shows that the change trend of the dynamic elastic modulus and damping ratio of the specimen with axial strain under bidirectional cyclic loading is similar to the change trend of the dynamic elastic modulus and damping ratio of specimen with uniaxial cyclic loading with axial strain.Obvious nonlinear characteristics;the inflection point of the maximum dynamic elastic modulus and the maximum damping ratio with the content of P5 is at P5=70%.For the samples with the same P5 content,the dynamic elastic modulus attenuation curve of the bidirectionally cyclically loaded sample is always below the dynamic elastic modulus attenuation curve of the unidirectionally cyclically loaded sample,and the damping ratio change curve of the bidirectionally cyclically loaded sample is always in one direction cyclically load the sample above the curve of the damping ratio.The hysteresis curve of bidirectional dynamic loading is arcuate,and the hysteresis curve of unidirectional cyclic dynamic loading is fusiform;the axial cumulative strain development curve of unidirectional cyclic loading and bidirectional cyclic loading are basically similar in shape,both showing rapid growth first and then the growth rate gradually decreases,and the final deformation tends to be stable.Most of the deformation of the sample is basically completed within the first 1000 cycles.In addition,under the same P5 content and the same cyclic stress ratio,the final strain of the sample under bidirectional cyclic loading is greater than the final deformation of the sample under unidirectional cyclic loading.large.5.Based on the axial cumulative strain data of subgrade fillers under different P5 contents,the HCA model?High-cycle Accumulation Model?of the large-scale cyclic cumulative deformation prediction model of subgrade fillers was improved.Introduce the influence factor fp5 of P5 content,get the expression and parameters of fp5 by fitting the test data,put forward the axial cumulative strain prediction model that can consider the influence of P5 content,and finally pass the verification test to prove that the improved HCA model can accurately predicting the long-term cumulative deformation of highway subgrades with different P5 contents under road cyclic loading.The result provides a new method for prediction and control of road settlement during long-term service. |
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