Study On Mechanical Behavior Of Baiheqiao Highway Tunnel With Sandy And Pebble Surrounding Rock

Sandy and pebble soil is a kind of granular material consisted of pebble and sand.Its mechanical behavior is different from sand and clay,which leads to differences in engineering characteristics.Barn effect is a common phenomenon of granular matter.This effect is that the pressure at the bottom of the does not increase linearly with the increase of the height of the filling particles,and will gradually reach a fixed value after reaching a certain height.Based on the Baiheqiao Tunnel of Weiwu Road,analyzed the mechanical behavior of the tunnel in sandy and pebble strata by theoretical analysis,DEM numerical simulation and field monitoring according to barn effect and Janssen model.Obtained some systematic rules,which lays a foundation for the study of load structure model of sandy and pebble tunnel.The main tasks were as follows:Firstly,analyzed and sum up the literatures concerned,summarized the existing research results of the sandy and pebble tunnel and status of particle material,which lays the foundation for follow-up work.Secondly,determined the macro and mesoscopic characteristics of sand and pebble stratum by means of combination of field experiment at site of Baiheqiao Tunnel and DEM simulation.Obtained the macroscopic parameters such as particle size distribution,water content and repose angle,and the mesoscopic parameters.Then,carried out the simulation of the barn effect,proved the rationality of the improved Janssen model,determined the important parameter steering ratio J in the formula,and found that the influence of the width of the model on the load is not obvious,verified that the judgment of deep and shallow buried tunnel is not applicable to the Baiheqiao tunnel.Studied the influence of the content of coarse particles on the load,found that when the content of coarse particles is 70%,the bearing capacity is the best,and explored the relationship between the side pressure coefficient,the steering ratio J and the content of coarse particles.Finally,studied the load distribution model of tunnel with different span in sandy and pebble stratum,and gave the correction coefficient of Janssen formula for vertical pressure of tunnel arch roof.Verified the load formula and correction coefficient by the original size model and the results of field earth pressure experiment.