The Adaptability Of Active Control Technology For Subway Tunnel Passing Through The Existing Structure

With the increasing density of urban subway network in China,new tunnels will inevitably cross under the existing tunnels.In order to meet the increasingly strict deformation control standard of the existing line,a series of active control measures need to be taken,such as grouting lifting and jack lifting.If not properly implemented,it may cause uneven deformation of the existing structure,or even cause local excessive stress concentration and damage.Therefore,it is necessary to study the adaptability of active control technology to achieve the ideal effect of uniform control structure displacement.Based on the engineering background of Suzhou Street Station of Beijing metro line 16 passing through the existing structure of line 10,this paper adopts case statistics,numerical simulation,theoretical analysis and other research methods,introduces the types and application status of active control technology,investigates the crossing engineering cases in Beijing,analyzes the adaptability of active control technology to different working conditions,summarizes the selection and application of active control technology scheme The implementation method has achieved the following main results:(1)Based on the investigation and statistics of the crossing engineering cases in Beijing,the paper summarizes the cross-section form,interlayer soil thickness,construction method,etc.of each case,summarizes and classifies the new tunnel type,cross-section size,existing structure type,construction method,auxiliary construction method,crossing angle,deformation joint and other factors,and summarizes six types of crossing conditions.(2)This paper analyzes the classification of grouting uplift and the four stages of grouting force,and analyzes the adaptability of grouting uplift under different conditions,such as different grouting pressure,different formation elastic modulus,different interlayer soil thickness,etc.The results show that the effect of grouting uplift gradually weakens with the increase of the elastic modulus of the stratum,and the weakening speed is slower and slower,and the smaller the thickness of the interlayer soil is,the more significant the effect of the stratum modulus on the jacking is.When the thickness of the interlayer soil is larger and the stratum modulus is larger,the effect of grouting uplift will be greatly weakened(3)This paper compares and analyzes the stress and deformation of the structure under the action of different arrangement and loading forms of jacks,and puts forward that jack lifting may cause greater stress concentration on the structure,resulting in the negative impact of structural damage.It holds that the jacking scheme can not be used as a conventional construction scheme,but only as an alternative and emergency scheme.If it is necessary to use it,it should be used as a jack arrangement scheme And the loading form is optimized to make the jacking force evenly arranged and multi-step and small amplitude loading to reduce the uneven lifting of the structure.(4)Based on the engineering example,the construction method optimization and comparison are carried out.According to the simulation excavation of construction steps,the construction scheme of excavating the left and right pilot tunnels first and then the middle pilot tunnels is determined.The deformation and stress of the existing structure are analyzed.After adopting the optimized jacking scheme,the settlement of the base plate of the existing line 10 station is reduced by 46.4%.(5)This paper summarizes the scheme selection and implementation points of active control technology,which should control the structure as a whole before,during and after construction,and pay attention to the timely monitoring of the structure in the construction process so as to find out the possible risks.