| In order to improve the mechanization and construction level of subway tunnel in rock layers,several cities of China began to explore the application of TBM during tunnel construction.DS-TBM with the advantages of geological adaptability and fast construction speed has been applied in the subway of Qingdao and Shenzhen subway.There is the gap of 10-20 cm between segment ring and surrounding rock in DS-TBM tunnel,which was filled with pea gravel.The pea gravel was backfilled and grouted to form an interaction system of surrounding rock-backfill layer-segment.The backfilled layer acts as connection layer of surrounding rock and segment ring,which has an important influence on structural behavior of segment and the deformation of surrounding rock.However,there is a lack literature about the backfilled layer and its effect by previous scholars.This leads to ignore the existence of backfilled layer in the design method of segment ring,the ground displacement and longitudinal deformation prediction,which has the difference with the actual engineering.Therefore,the theorical analysis,numerical simulation,scaled model and in-situ measurement were applied in this paper with the aim of the influence of backfilled layer.Firstly,this paper carried out the longitudinal division of DS-TBM,analyzed the spatial distribution of surrounding rock-backfilled-segment composite layer.Secondly,the structural behavior of segment was found out,and the design and deformation control method of segment ring,the prediction of ground displacement were proposed.The research results were concluded as below:(1)Based on the state of lining,4 construction stages of DS-TBM tunnel was divided.Further,the spatial relationship between surrounding rock-backfill layer and segment was found out.Moreover,the stress characteristics,the longitudinal deformation of segment ring and the surface settlement characteristics of tunnel in each phase were concluded.It is emphasis that the backfilled layer has a significant influence on the longitudinal deformation and ground settlement of tunnel.(2)The mechanical mechanism and structural behavior of segment were found out through the scaled model.The results concluded that the backfilled layer should be acted as the generalized layer,rather than the conventional bearing layer.And the calculation of backfilled-surrounding rock coefficient was proposed.Further,the design model of DS-TBM was established,forming the design method of DS-TBM in subway engineering.(3)The mechanical characteristics of pea gravel were proposed with the triaxial shear experiment.The deformation of pea gravel-surrounding rock foundation was found out,and the non-linear calculation of pea gravel-surrounding rock foundation.Therefore,combined with the proposed shear stiffness calculation of longitudinal joints,the longitudinal deformation calculation model considering pea gravel in straight and turning phase was proposed.The influence of pea gravel,joint stiffness,the radius of turning,the jack force on the longitudinal deformation were concluded,and it is highlighted that the ratio of pea gravel is the key point of these facts.So the control measures of longitudinal deformation were proposed.(4)The influence of pea gravel and particle migration on ground settlement were carried out and especially the ratio of pea gravel is the key point for ground settlement.Furthermore,the Peck and mirror image calculation of ground settlement in DS-TBM considering the volume of pea gravel was proposed respectively.And the theorical calculation was validated with the in-situ results.Meanwhile,the control value of the ratio and volume of pea gravel were concluded. |
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