Research On Deformation Mechanism Of Open Shield Tunneling In Waterless Sandy-cobble Stratum

In recent years,with the development of infrastructure construction in our country,as a special tunnel construction equipment,shield machine is widely used.more and more shield tunnelling machine are used in construction of tunnel and underground engineering.The first issue in Shield tunnel construction is the selection of shield machine,appropriate shield tunnelling machine choice is the key to success or failure of shield tunnel construction.various shield machine also has a certain scope of application.A correct choice should be considered formation adaptability,safety,economy,and smaller impact on the environment requirements,and determine after economic and technical comparison.Sandy-cobble is a special stratum for tunnel construction.Sandy-cobble has large particles,it’s viscosity is low and rigid contact between particles,etc.Practice has proved that the compacted without water(or less water)sandy-cobble stratum has better stability,choose open shield machine can make full use of the formation of the stability.Then the cutter wear can be avoided,the down time can be reduced and improve efficiency.This thesis used particle discrete element numerical model and the physical scale model,studied the excavation deformation mechanism of sandy-cobble stratum.The following works had been done in this paper:1.No supporting excavation of sand-cobble stratum particles mobile mesoscopic mechanism researchBased on particle discrete element program PFC3 D platform.Establish sandy-cobble stratum numerical model.Carried out no supporting excavation experiment.Comparing and analyzing by changing parameters,The effects of different roughness coefficient,different depths on the unloading characteristics of sand and pebble soil were systematically studied.The quantitative analysis of the loose degree,deformation and soil movement law of sand and gravel strata under excavation unloading is carried out,By track the progressive failure process,the mesoscopic mechanism of the excavation of the sand and gravel strata is explored,which provides areliable mechanical basis for effectively controlling the stability of the excavation surface of the sand and gravel stratum.2.Study on the relationship between open shield tunneling parameters and soil movement law of sandy-cobble stratumBased on the understanding of the mesoscopic mechanism of the excavation of the sandy-cobble stratum,the effects of four different supporting forms on the loosening degree of the sandy-cobble stratum,the deformation of the formation and the law of soil movement are analyzed,which provides a reliable reference for the actual engineering excavation parameters.carry out a similar model test on the four supporting forms of support excavation.The non-contact measurement are used for monitoring soil deformation,and perform digital image processing and analysis.The degree and range of sandy-cobble stratum movement and the possible form of instability.Those results are compared with PFC3 D numerical results.In this paper,the numerical calculation and theoretical analysis of particle discrete elements are used to study the mesoscopic mechanism of contact and occlusal mechanism and excavation unloading deformation in sand and gravel stratum,and analyzes the influence of meso-structure on its strength and excavation stability.Explains the support degree of excavation surface from the meso-mechanism,so as to provide scientific basis and theoretical support for the open-type shield of sandy-cobble stratum.