Research On The Bearing Mechanism Of Geogrid Reinforced Pile Supported Embankment Under Static And Dynamic Loads

As an important infrastructure,railway plays an important role in China’s transportation network.Pile network structure roadbeds are widely used in domestic high-speed railway roadbed projects due to their short construction period and low post-work settlement.However,the force mechanism of pile network structure roadbed is very complex,and the research on its load transfer,distribution law and dynamic response is not sufficient.In this paper,laoratory tests and finite element methods are used to study its load transfer law,and the main work is as follows:(1)The stress-strain of the piles,the pile-soil load sharing ratio,the soil pressure distribution inside the embankment,the development and distribution of the soil arch effect,and the stress distribution characteristics of the grid bedding layer were investigated through large scale laboratory model tests.The test results show that:the pile bearing capacity is mainly expressed as pile lateral friction resistance;the tensile force of the geogrid decreases in the transverse direction from the centre of the embankment to the foot of the slope;the transverse soil pressure of the roadbed is greater than the longitudinal direction;the limit state of the spatial soil arch effect occurs at about 3.8 pile soil stress ratio,and the limit state of the planar soil arch effect occurs at about 2.2 pile soil stress ratio,and the spatial soil arch effect is stronger than the planar soil arch effect.stronger than the planar soil arch effect.(2)By applying dynamic load to the pile network structure,the pile soil stress distribution,embankment soil dynamic stress distribution and the development of soil arch effect under dynamic load were investigated and compared with the static load test,and the results show that:the soil arch effect under dynamic load is definitely attenuated compared with static load,and the stronger the soil arch effect under static load,the greater the degree of weakening under dynamic load;the change trend of soil dynamic stress between piles with vibration is similar to the "N" type,which is the opposite of the change trend of soil dynamic stress at the top of piles;the grating tension under dynamic load is about twice that under static load of the same size.(3)A three-dimensional numerical calculation model of the pile network structure roadbed is established to reveal the load transfer law and dynamic response law of the structure.The influence of the main parameters such as embankment fill height and pile spacing on the mechanical properties of the pile network structure roadbed and the soil arch effect is analysed.The dynamic response of the structure was simulated for a train load at a speed of 300km per hour.The results show that:the load transfer of the geogrid is wavy from the central axis of the embankment to the foot of the slope;the soil arch is waved in the cross section of the embankment;the increase of the pile spacing can increase the height of the soil arch and expand the influence range of the soil arch effect but the strength of the soil arch will be weakened;the influence of the embankment height on the soil arch effect is not obvious;the distribution characteristics of the soil arch effect inside the embankment under dynamic load are the same as that of static load,but it is significantly weaker than that of static load.