Research On Deformation And Destruction Characteristic Of Sandy Cobble Surrounding Rock Of The Highway Tunnel

The Sandy cobble stratum is the granular packs which composed of pebble and different particle size of sand and soil.With the development of a large number of urban tunnels,the security problems caused by crossing the cobble stratum have attracted more and more attention.In order to further research the deformation and failure regularity of the tunnel after excavation which in the sandy cobble formationIn this paper,the engineering characteristics of sandy pebble soil are studied through the comprehensive research method of The theory analysis and comprehensive research method and discrete element numerical simulation test.Quantitatively analyzed the influence of moisture content and density of the tunnel surrounding rock,some systematic laws are obtained,which lays the foundation for the study of stability analysis of sandy cobble surrounding rock of tunnel.The main results are as follows.(1)Through indoor triaxial test and numerical triaxial test contrast,obtained the mesoscopic parameters under different working condition of different moisture content and compactness,through different radius of stress circle extraction of gravity stress calculated with the actual gravity stress contrast suitable stress circle radius.(2)In natural moisture content(1.5%),moisture content of 4% and moisture content of 6% cases,the judgement of buried depth in sandy cobble stratum is consistent with the experience,but in saturated moisture content(8%)cases,buried depth judgement need according to the actual situation to determine,then simulate the surface subsidence curve equation of the shallow buried tunnel after excavation.(3)In the case of dense and middle dense,the judgement of buried depth in sandy cobble stratum is consistent with the experience,but in the case of loose,buried depth judgement need according to the actual situation to determine,then fitting the surface subsidence curve equation of the shallow buried tunnel after excavation.(4)Sandy pebble formation step method of tunnel excavation,invasion degree of surrounding rock and vaults caving arch height increases with the increase of moisture content of sandy pebble and sandy pebble compactness.And calculated under different working conditions(different moisture content and different compactness)invasion of the size,morphology of surrounding rock arch height and width,then fitting the cave arch curve equation.(5)Sandy pebble formation step method of tunnel excavation,close to the next step excavation of surrounding rock of the tunnel free face when the movement rate slightly larger when compared with the previous step excavation.(6)Primary support C30 modulus of concrete has good supporting effect of sandy pebble tunnel surrounding rock.