| Geogrid-reinforced and pile-supported(GRPS)embankments,as a new type of foundation treatment method,has been widely used to construct high-speed railway in China due to their good bearing capacit and small differential settlements.The soil arching and reinforced cushion are the main factors affecting the load transfer of GRPS embankments.However,the design of GRPS embankments is mainly based on static achievements at present.Actually,not only bears the static load of the superstructure,but also is subjected to the long-term dynamic load of the train.Thus,the soil arching is inevitably influenced by long-term train dynamic loads and will lost stability and degenerate under certain conditions,meanwhile influencing the bearing capacity of reinforced material in cushion.These will cause stress redistribution and then lead to deformation of embankment as well as track structure and finally influence running safety and comfort.In view of the above problems,based on the existing static research results,through numerical analysis and laboratory model experiments,this paper studies the influence of train dynamic load on the load transfer law of GRPS and the bearing capacity of reinforced cushion.The main conclusions are as follows:(1)Through numerical analysis,considering the influence factors of subgrade height,geogrid stiffness and soil stiffness,the influence of train dynamic load on soil arching of GRPS embankments is studied:(1)When a complete soil arching is formed in the subgrade,the train dynamic load has little effect on the soil arching,but it will cause the degradation and instability of the incomplete soil arching in the low subgrade.(2)The existence of geogrid can significantly reduce the influence of train dynamic load on soil arching,but the effect is not obvious when the grid stiffness is increased;when the soil stiffness between piles is small,the effect of dynamic load on soil arching is more obvious.(2)Through the laboratory model experiments of GRPS embankments,considering the two cases of geogrid or not,100,000 times of dynamic loads were carried out.The changes and distributions of dynamic and static stress on pile and soil,the development of strain of geogrid and the change of load-sharing ratio of pile were mainly studied:(1)Under static load,the soil arching is obvious.The height of soil arching is about1.38 times of the pile net distancean and load transfer is mainly affected by the soil arching.Under dynamic load,the transfer of load in roadbed is mainly affected by geogrid and soil arching.At this time,the pile-soil stress ratio of geogrid test is 5.9,which is larger than 3.5without geogrid.The existence of geogrid obviously improves the pile-soil stress ratio,thus increasing the stability of soil arching under dynamic load.(2)Under dynamic loads,the load transfer mainly occurs in the range of soil arching(h/s < 1.38).With the increase of the number of cycles,the dynamic stress above the soil on piles increases exponentially in the form of ?_d=a*N~b and the increment without grids isobviously greater than that with grids.After the end of cyclic load,the pile efficacy in the two groups of tests decreased by 2% in the test with grille and 7% in the test without grille.Geogrid obviously changed the way of load transmission,and made the pile bear more load.(3)After 100,000 dynamic loads,the bearing capacity of geogrids has changed,which shows that the increment of dynamic strain is larger than that of static load,and the tension of geogrids will degenerate and soften.(3)Considering the dynamic constitutive model of geogrids,the effects of cyclic load,pre-tension and load frequency on the bearing capacity of geogrids are studied by numerical analysis.The results show that before cyclic loading,if the geogrid is subjected to a certain pre-tension,it will have a greater impact on its load-bearing performance;at the same time,the loading frequency also has a greater impact on the load-bearing performance of geogrid. |
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