Research On Construction Control Standard Of Shield Tunnel Underpassing Existing Tunnel In Water-rich Compound Stratum

With the rapid development of the national economy,urban rail transit has been gradually networked and scaled in the major cities of our country.Due to the late start of subway construction in most central and western cities in China,the shield tunnel construction technology and the corresponding control standards that are compatible with the city geology have not been formed in each city.Meanwhile,with the new phase of rail transit construction boom in cities in central and western China,it is difficult to avoid that the rail transit lines constructed in the later period will need to cross the rail transit facilities that have been built or even in operation.Therefore,in order to ensure the efficiency and safety of urban subway construction,it is the primary problem for every city to establish perfect shield tunnel construction technology and corresponding control standards that are compatible with its own city geology.Based on the tunnel between the South Station of Dinggong road and the North Station of Dinggong road of Nanchang Metro Line 4,this paper takes the tunneling parameters of shield machine and the existing tunnel as the research object.Four methods,including data collection,field investigation,theoretical analysis and numerical simulation,are used to study the formation adaptability of shield tunneling in water-rich composite stratum,the control standard of tunneling parameters,the risk assessment of the existing tunnel structure and the settlement control standard in the process of underpassing the existing tunnel.The main research contents are as follows:(1)Based on the characteristics of engineering geology and hydrogeology that Nanchang Metro Line 4 passes through water-rich composite stratum,this paper studies the type selection of shield machine in composite stratum from the aspects of stratum permeability,construction technical difficulties,construction period,construction environmental protection and temporary construction land.The type of shield tunneling machine suitable for the geological conditions and the corresponding reconstruction measures are determined.Combined with the field tunneling parameters of shield tunneling machine,the adaptability of shield tunneling machine to composite strata is analyzed statistically.(2)Based on PFC3 D discrete element analysis software,a discrete element numerical model of full hob rock breaking in composite strata was established.By analyzing the correlation between the shield tunneling parameters and the rock breaking force of the hob,the relationship between the maximum tunneling speed based on the rock breaking force of the hob and the rotation speed of the cutter head is proved.According to this,the tunneling parameter control standard of shield tunneling machine in composite formation is established.(3)The risk assessment system of the existing interval tunnel structure is established,and the risk assessment of the interval structure of the existing Line 2 is carried out according to the project of Nanchang Metro Line 4 crossing the existing Line 2,and the risk level of the existing interval structure is determined.(4)The three-dimensional numerical model of shield tunnel under the existing interval tunnel is established,and the relationship between the structural settlement deformation and structural damage failure of the existing tunnel is analyzed.Based on this,the control standard of the interval settlement of the existing rail transit in Nanchang area is established.