Research On The Disturbance Mechanism And Counter Measures Of Shield Tunnel Crossing Upper-soft Lower-hard Stratum

Upper-soft lower-hard ground is often met in shield tunnel construction of special geological conditions.Due to the inhomogeneity of the characteristics of the excavation surface,there are many problems in the process of shield tunneling in the "soft and hard uneven stratum",such as the poor attitude of the shield,the local stress concentration of the segments,and the difficulty of controlling the surface settlement,which is hard to protect construction quality and construction period.It is of great significance to improve the safety and rapid excavation of the shield tunnel in the upper and lower soft strata of the shield tunnel in the process of excavation of the shield in the upper soft and hard strata.Based on the shield tunneling traversing upper-soft lower-hard ground of Shenzhen Subway Line 7,this thesis systematically analyze the mechanism of stratigraphic disturbance caused by shield tunneling in upper-soft lower-hard ground from the macroscopic and miso-level by means of theoretical analysis and discrete element numerical simulation,which also discuss the stratigraphic improvement.And combining influence of different tunneling parameters on formation disturbance with on-site statistical data on tunneling parameters,the 'optimization study on the tunneling parameters of the upper and lower brackets is carried out.The main results are as follows:1?Based on the theoretical analysis of the perturbation mechanism of shield tunneling in the upper-soft lower-hard ground,the numerical simulation model of the three-dimensional particle flow is used to simulate the disturbance caused by shield tunneling in the upper soft and hard strata.The stratospheric disturbances caused by shield tunneling in the upper soft and hard strata are proposed.2?Taking into account the mechanism of hobbing rock breaking,proposes the simulation method of hobbing rock breaking in the hob model with the first and second rotation of the cutter head by calibrating micrometer parameters of the lithologic stratigraphy and establishing the earth pressure balance shield machine(including cutter head,scraper,hob,silo and shield)-three dimensional discrete element model of upper-soft lower-hard ground with particle flow discrete element analysis software PFC.3?By comparing and analyzing the relationship between the soil particles contact state,the particle displacement and the stress of the formation in the stratum related to the formation disturbance caused by the tunneling in upper-soft lower-hard ground under the case of 25%,50%and 75%of the hard rock,And the perturbation law of shield tunneling to surrounding strata under different conditions is proved.4?Using three-dimensional numerical simulation to simulate the formation disturbances caused by shield tunneling under different stratigraphic conditions and tunneling parameters.It is proved that the reinforcement of soft soils can effectively reduce the influence of shield tunneling on formation deformation and internal force of segment;the results show that the parameters of the top thrust,the excavation speed and the cutter speed of the shield are given when the shield passes through the soft and hard strata.