| Recent years,there are more and more long hydraulic tunnels having been built in China with the appearance of regional or inter-regional water transfer projects.Tunnel excavated with TBM and subsequently supported by segmental lining can exactly decrease construction difficulty,improve the efficiency and security,which makes it the main choice for the excavation of long-distance tunnel.For segmental lining,staggered joint assembling can exactly improve the mechanical and impervious property compared to straight joint assembling,moreover,rectangular segment is the main current segment type for it.While parallelogram segment proposed in this study,as a newly kind of segment,can be assembled faster and easier with staggered joint compared to the former,since every specific segment has same position and assembly sequence in different rings by the way of advancing on the whole.However,its corners may suffer dangerous stress states due to the inclined angle between the joint surface and the tunnel axis.Therefore,three-dimensional(3D)strata structure model with lining is built using the commercial finite element software ABAQUS based on a practical project.The 3D model includes surrounding rock,pea gravel,segmental lining and bolts,and the contacts are used to simulate the force transfer between adjacent segments or segments and pea gravel.The model is used to investigate mechanical characteristics of parallelogram segment under typical force conditions to providing support for wide application of the segment.The main contents and conclusions are listed below:(1)Building 3D model with nine rings assembled by parallelogram segment of 15° inclined angle,to investigate the mechanical characteristics of lining segment bearing jack force under single shield mode.Uniform(to advance straight)、right eccentric(to advance with left deviation)and low eccentric(to advance with upward bias)jack force are considered respectively,since typical driving postures of TBM usually include advancing straight,advancing with upward/downward bias or advancing with left/right deviation in practical projects.It can be concluded that: stress concentrations appear in the interaction between circumferential and longitudinal joints of lining rings closed to the jack when advancing straight.Along longitudinal axis,the end regions of joints are mostly open,while the middle regions are closed;segment malpositions are obvious,and compatibility of deformation of the whole lining is good;besides,under right eccentric force and low eccentric force,the stress concentrations in segment corners are further strengthened,segment malpositions are more obvious,and compatibility of deformation is lower.(2)Building 3D model with three rings assembled by parallelogram segment of 15° inclined angle,to analyze the structure characteristics of segment lining under high internal water pressure and the impact of lack of circumferential bolts in different joints.Under internal water pressure,the lining has outward deformation,and the circumferential stress is mainly tensile stress;segment joints are all in open state,the joint opening of one side near the lining outer surface is wider than that near the inner surface;all circumferential bolts are under tensile stress state,while the stresses are various.Besides,under internal water pressure,lacks of circumferential bolts have an effect on the stress and displacement of segments compared to normal condition,the regions with large stress of segments on both sides shift to neighboring joints respectively,and the joint opening increases while the openings of neighboring joints decrease.(3)Building 3D model with three rings assembled by parallelogram segment of 15° inclined angle,to analyze the structure characteristics of segment lining under external water pressure and the impact of lack of circumferential bolts in different joints.Under external water pressure,the lining segments bear the force as a whole,and the lining has inward deformation;the circumferential stress is mainly compressive stress,while inner side is larger than outer side;there appear stress concentrations near the joints.All segment joints are in closed state,the pressure on one side near the lining inner surface is larger than that near the outer surface;all circumferential bolts are under compressive stress state,and the stresses are small.Besides,lacks of bolts under external water pressure have no effect on mechanical properties and joint states compared to normal condition.(4)By changing the segment joint inclined angle,two different models are built: one model with 9 rings under jack force,another model with 3 rings under internal and external water pressure,to investigate the structure characteristic variation of segment lining with different inclined angles.When the jack force applies on the lining,as the segment angle increases,the stress concentrations are strengthened in the joints,the heterogeneity of displacement increases;and the nonuniformity of opening/pressure of joints is larger.When the internal water pressure applies on the lining,the tensile stresses in central parts,joint openings and circumferential bolt stresses are all decreased,while the maximum tensile stress appearing in bottom groove increases.When the external water pressure applies on the lining,the maximum compressive stress becomes larger slightly as the segment angle increases,while the stresses in both ends along circumferential direction and joint pressure are all decreased obviously.Above all,for parallelogram segment,as the increase of joint inclined angle,stress concentrations appearing in joints are strengthened and the variations of joints are larger under jack force,which is unfavorable for joint safety and water seal;joint openings under internal water pressure and joint pressures under external water pressure are smaller,which is more benifical for seepage prevention during operation period and joint safety during overhaul period.Therefore,parallelogram segment should be avoid under single shield mode and used in double shield mode,and filling treatment of the bottom groove should be adopted,which can take full advantage of it in improving construction speed with structure safety. |
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