Study On Stability And Environmental Impact Of Jacking Pipe

With the development of underground structure in China,pipe jacking engineering has become a hot topic of research at home and abroad.Most scholars only study it according to a certain working condition or characteristic of pipe jacking engineering.On the basis of previous studies,this paper studies the influence of pipe fitting stability and environment in pipe jacking construction by using finite element software combined with field measurement.The main research contents are as follows: first,foundation pit safety monitoring;Second,structural stability analysis of steel pipe jacking under various loads;Thirdly,stability analysis of prestressed steel tube concrete pipe jacking;Fourth,ground deformation research during pipe jacking construction;Fifth,the influence of pipe jacking construction on adjacent pipelines.The results show that :(1)the accumulative changes of the five times of water level monitoring are all within the range of warning value,and the fourth time of water level change is 222 mm/d,which exceeds the warning value.At the depth of about 18 m,the displacement of the supporting structure is the smallest,and the displacement of the supporting structure increases with the increase of time.The soil movement curve finally presents a folded line,and the overall displacement trend at the measuring point of the supporting structure is to move towards the inside of the foundation pit.(2)Under uniformly distributed confining pressure,the increase of wall thickness will increase the ultimate bearing capacity of steel tubes;Under uniform axial load,the ultimate bearing capacity of steel tube decreases with the increase of its length.When the grouting is good,the friction resistance of pipe and soil is stable at 3-4kpa.Under the loading of confining pressure,head-on resistance and friction resistance,the axial pressure stability of steel pipe jacking is greatly affected by the buried depth.After the pipe reaches the buckling confining pressure,its axial bearing capacity decreases rapidly.The measured results show that the head-on resistance fluctuates around 240 k N,and the jacking velocity fluctuates around 20mm/min.The variation law of head-on resistance and jacking velocity is basically opposite.3)When JPCCP pipe is jacked symmetrically,the displacement variation trend of jacks is the same and the stress is the largest,and the overall force at the back end of the pipe is uniform.The maximum displacement of the pipe when six jacks are jacked is not different from that when four jacks are jacked.The maximum displacement of the pipe is about half of the displacement of the pipe when the two jins are jacked into the top.When the pipe is pushed forward asymmetrically,the radial displacement is formed at the pipe end,the overall force of the pipe is not uniform,and axis deviation is easy to occur,but the structures are in a safe range.In JPCCP jacking monitoring,the relationship between the jacking force and the jacking distance can be approximately fitted as a direct proportional function.(4)During jacking operation,the soil will heave slightly before tunnel excavation.The settlement value at the jacking section and the place nearest to the pipe jacking axis is larger than other positions,and the lateral stress of the pipe is relatively large.(5)When pipe jacking is applied to adjacent single buried pipe under construction,the stress of pipe with different stiffness is obviously different,and the stress near the axis of pipe under construction is the largest;The displacement of different pipes is similar,and the displacement is the largest above the adjacent pipe side.The displacement of pipeline under construction increases gradually with the increase of radius,so the pipe with small diameter should be selected as the priority in design.The stress and displacement of the adjacent buried pipe close to the jacking pipe under construction are larger when the pipe is applied to two adjacent buried pipes.