Effect Of Tunnel Collapse On Shield Tunnel Structure In Collapsible Loess Area And Its Treatment

In recent years,most of the subway's construction in Xi'an need to go through the collapsible loess area,while the collapsible loess in natural humidity has low compressibility and high strength,with the effect of water the strength reduces significantly,the deformation becomes large and changes fast,which has a great damage to the structure.Therefore,it is necessary to study the influence of the characteristics of the collapsible loess on the subway structure,and to seek the practical treatment method according to the engineering characteristics.Based on the section between Zixia one road and Zixia three road,the project of Lintong line in Xi'an subway,this paper studied the stress and deformation characteristics of collapsible loess foundation of the bottom of tunnel and optimized and verified the treatment technology through the centrifugal model test and numerical simulation,The main contents and conclusions of this paper include the following aspects:1?The results of the centrifugal model test and numerical simulation reaval the characteristics of stress and deformation of the tunnel structure under the conditions of full collapse of the tunnel,the horizontal half collapse of the tunnel,and the longitudinal half collapse of the tunnel,and show that the deformation of the tunnel structure caused by even collapse is larger than that of the half collapse,and the stress of the tunnel structure caused by half collapse is larger than that of the even,especially the influence of the tunnel bottom horizontal half collapse on the circumferential internal force and the tunnel bottom longitudinal half collapse on the longitudinal axial force.2?The results of centrifugal model test and numerical simulation show that the even collapse of the tunnel and the uneven collapse may adversely affect the tunnel structure.Therefore,it is necessary to carry out the foundation treatment of the collapsible loess of the tunnel bottom and do well in the water seepage measures to avoid the negative effect caused by the water.3?Using the numerical simulation the depth,treatment range and pile spacing of the three-axis mixing pile are optimized.The results show that the bearing capacity of the foundation is gradually increased with the increase of the treatment range,the replacement ratio,and the water immersion's effect on collapsible loess of the tunnel structure is gradually enhanced.Through the comparison and selection of the treatment parameters,the two equation of the relationship between the settlement of the characteristic points of the tunnel and the processing parameters is fitted,which can make a reference to the engineering practice.4?The preferred treatment is verified through numerical simulation and centrifugal model test.It is known that the law of the mechanical deformation of the tunnel after the foundation treatment is consistent with the treatment when compared with the pre-treatment.Due to the improvement of the bearing capacity of the foundation,the deformation and stress changes are within the safe range of the control standard.It is proved that the optimized treatment technology can satisfy the safety of the shield tunnel under the condition of even and uneven settlement of tunnel bottom.