Effect And Control Of Neighboring Pile With Shallow Tunnel Construction

It is well-known that surrounding environment must be disturbed by the stratum deformation and stress relieving induced by tunnel excavation when underground works are constructing in urban using shallow mining method.Especially constructing shallow depth bored tunnel in Beijing of which the main ground traffic style is based on overpass and circuit,many existing overpasses will be crossed by tunnels and the normal operation of them will be affected inevitably.As new construction climax of the metro lines is coming in Beijing now,the number of this phenomenon is increasing,and the following contradictions will become sharper.So, it's very important to study on the effect and control method for adjacent pile foundation.In this paper,based on domestic and foreign documents,integrated existing project experience,combined theoretical analyse with numerical modeling and taking line 4,5,10 in Beijing and South-to-North water diversion engineering for example,systematic and intensive research on key technique,theoretical basis,control system and so on will be made.And a series of research findings are obtained.(1)In the light of characteristics of crossing existing pile foundations by shallow mining method,the interaction relationship of tunnel-soil-pile-superstructure are given and the key factor of controlling the influence to the pile foundations be controlling the ground deformation;(2)According to the basic theory of bearing capacity of pile foundation and considering the characteristics of stratum deformation caused by shallow mining method in Beijing,the deformation model and stress mechanism of existing pile foundation in different ground deformation mode are studied and the relevant model and control method are established.(3)Concept of bearing capacity loss of pile induced by tunnel construction is put forward,which suggested that the settlement of exiting pile foundation is caused by bearing capacity loss of pile and established the relationship between them by theoretical derivation.It is approved that the bearing capacity loss of pile can be controlled by settlement of pile foundation.(4)Through five cases including"the difference of vertical distance between the tunnel face and pile foundation,""the different vertical and horizontal distance when the tunnel under crossing the pile foundation,"and"the different vertical and horizontal distance when the tunnel side crossing pile foundation",and considering the influence degree of the four indicators,such as pile foundation settlement,horizontal displacement,axial force and bending moment during tunnel construction,classified the influencing degree to pile by construction as grade 1,2,3and4 from weight to light, provided application basis to using fuzzy comprehensive evaluation method to evaluate capacity influnce of pile foundation.(5)According to the research findings mentioned above,a systematic risk control system of existed bridge during the shallow mining field construction is established. The key to this system is movement allocation method base on dynamic mechanical analysis principle.And it is successfully used in practical engineering.