Mechanical Characteristics And Settlement Prediction Of Shield Tunnel Under Compound Stratum In Flight Area

The construction of shield tunnel under the airport flight area should ensure the safety of the tunnel construction processandavoid the excessive settlement of the airport road surface caused by the shield constructionwhichwillaffect the normal take-off and landing of the aircraft,besides,it needs to consider the impact of the moving load of the aircraft on the structural safety of the underpass tunnel.However,it is more difficult to construct shield tunnel in the upper-soft and lower-hard composite stratum of the airfield,and the mechanical properties of segments are more complex.Based on the project of Shenzhen Bao’an International Airport under which is the shield tunnel of SHZ-9 bid of Guangzhou-Shenzhen inter-city railway,this paper studies the practical engineering problems by means of data investigation,theoretical analysis,numerical simulation and field monitoring.The response range of the soil under the pavement caused by the load of a large aircraft,the mechanical characteristics of the shield tunnel segment in the composite stratum in the flight zone,the response of the composite stratum tunnel caused by the movement of the aircraft,and the law of surface settlementcaused by the construction of the shield tunnelin the composite stratum of the airfieldhave been analyzed in this paper.The main research contents and results of this article are as follows:(1)Based on the Boussinesq solution and elastic layered theory,the additional stress formula of soil at any depth under aircraft load is derived;based on the derived formula,the law of additional stress value generated by three aircraft loads,Airbus A3 80-800,Boeing B-747-400 and B-777-300ER,is analyzed by Matlab,and the position of the maximum vertical stress acting point of three large aircraft is determined;by analyzing the change law at the maximum additional stress pointof the three types of large aircrafts in different directions,it is obtained the calculation formulas of the influence range of three large aircraft loads on the shield tunnel in the flight zone at different depth.(2)Through the numerical simulation,the mechanical characteristics of the segments atdifferent depth and different composite ratio of the strata in the cross section of the tunnel are studied.It is found that the deformation and axial force of segments are greatly affected by the overburden depth,but less affected by the overburden ratio;the bending moment of segments is less affected by the overburden depth and more affected by the formation composite ratio.(3)Considering the influence of the most unfavorable aircraft load,through numerical simulation,this paper studies the response law of the segment of the shield tunnel in the composite stratum in the flight area under the action of the aircraft moving load.When the aircraft load is directly above the tunnel,it has the greatest influence,and the response of the segment of the tunnel caused by the aircraft load affected by the stratum factor is different at the stratum boundary.(4)This paper presents a monitoring method for ground settlement during shield tunneling of airport flight area.Based on the settlement of the airfield pavement measured data,it got the revised Peck subsidence prediction formula which issuitable for the engineering sectionby introducing revision coefficient and,when the correction coefficient within the range of 0.5～0.9,within the range of 1.0～1.4,the calculated Peck prediction formula can accurately predict the settlement of airport pavement caused by shield tunnel construction in the composite stratum of the flight area in this section,which has important engineering guiding significance.