Study On Effect Of The Active Ground Fissure On Metro Tunnel And Its Hazards Control

Since the 1950s,there has already occurred a large number of ground fissures in urbanarea of Xi'an successively in Northern China because of the natural and artificial factors,etc.,tremendous losses have been caused by ground fissure hazards.Above all,these active groundfissures make a serious threat on Xi'an metro construction.,so it is very great and importantchallenge for Xi'an metro to go through these active ground fissures,and recently becomemore and more attention to scholars and engineers.On the background of Xi'anmetrotransversing the active ground fissure zones,the future active tendency of the groundfissures in Xi'an are analysed and the maximum vertical active displacements of groundfissures in the design life time of metro tunnel as 100 years are estimated.With large-scalemodel test and FEM,the deformation and failure mechanisms of metro tunnel with differentstructural styles are studied under the action of active ground fissure,then the hazards controlmeasures of metro tunnel passing through the active ground fissures are proposed in thedissertation.The major works and results of this dissertation are as follows:(1) From the view of regional tectonic movement and excessive extraction of groundconfined water once again,the future active tendency of the ground fissures in Xi'an isanalyzed.The maximum vertical displacements of active ground fissures in the 100a life timeof metro tunnel are estimated based on the present active speed,historical maximumdisplacement (offset) and active grade of ground fissures,which can be adopted as importantparameters for tunnel structural design of Xi'an metro going through the active ground fissurezones.(2) With large-scale model tests and finite element numerical simulation method,thedeformation and failure mechanisms of metro tunnel with different lining styles includingopen-cut rectangle box,shallow bored horseshoe and shield segment lining are disclosuredunder the condition of metro tunnel intersecting orthogonally and obliquely active groundfissure zones.(3) Based on the results of numerical simulations for metro tunnel going through active ground fissures,the longitudinal deformation equation of metro tunnel under the action ofactive ground fissure is proposed as y=A·x~3+B·x~2+C·x+D,in which A,B,C,D isconstant,the equation can be used to analyze the longitudinal behaviors of metro tunneltheoretically.(4) The variation laws of soil pressure,displacement of surrounding rock of metro tunneland ground surface settlement under the action of active ground fissure are obtained throughthe large-scale model test,which can be provided as the reference to city lay-out and buildingdesign along the metro lines in Xi'an.(5) For the present problem of most Xi'an metro lines passing obliquely through manyactive ground fissure zones,the effect of intersection angle with active ground fissure ofmetro tunnel on metro tunnel lining structure is studied with FEM,and the deformation andfailure characteristics and ranges of influence zones of tunnel are determined.(6) According to lining types of metro tunnel and their spatial intersection with activeground fissure,the deformation and failure modes of metro tunnel under the action of activeground fissure are put forward firstly in this dissertation on the basis of large-scale model testsand numerical stimulations,namely,the failure modes of tunnel with integral lining aredivided into tensile-squeezing failure when intersecting orthogonally with active groundfissure and tensile-torsion shear failure when intersecting obliquely with active ground fissure;the failure modes of shield tunnel are divided into directly-shear failure when intersectingorthogonally with active ground fissure and torsion-shear failure when intersecting obliquelywith active ground fissure.(7) Based on the large-scale model test and FEM,the calculation method of longitudinaltreatment length of metro tunnel passing through active ground fissure is proposed andapplied to determine appropriately the structural longitudinal lengths of Xi'an metro in theactive ground fissure zones.Three dimension moving mode and calculation formula ofsegmented tunnel under the action of active ground fissure is developed,with which thereserved displacements for the anti-crack design of metro tunnel are obtained.(8) With large-scale model tests of open-cut box tunnel and shallow bored horseshoetunnel intersecting orthogonally and obliquely with active ground fissure zone individually, the adaptability of sectionalized tunnel passing through active ground fissure is studied,theresults show that the sectionalized tunnel with flexible joint can bear very large sheardeformation,and the deformation and secondary stress of adjacent sectionalized tunnel underthe action of ground fissure is small,meantime many sectionalized tunnels can eliminatepartly the effect of active ground fissure movement,have a good capability of adapting itselfto the large deformation.(9) According to the particularity and complexity of Xi'an metro going through theactive ground fissure zones,on the basis of analysis of metro engineering hazards induced bythe moving of ground fissure,metro hazards control measures are proposed from thefollowing aspects as structure,waterproof,foundation treatment,and track adjustment etc.,which can be provided as the reference to structure design of metro tunnel passing through theactive ground fissure zones.