The Mechanism Of Long Distance & Large Section Concrete Pipe Sticking

With the widespread application of pipe jacking in the fields of municipal infrastructure construction,energy transportation engineering,water conservancy and hydropower engineering,large-section pipe jacking engineering has become increasingly widespread.With the increase of jacking distance,the depth of jacking and the complexity and diversity of geological conditions,different engineering problems appear in jacking construction.This paper is based on Chongqing Technological Innovation and Application Demonstration Project(Key Research and Development Projects of Social and People's Livelihood),relying on Guanjingkou Water Conservancy Project of Dongquan Town,Banan District,Chongqing.According to the pipe jacking problem of concrete pipe jacking joint during the construction of the pipe jacking project,combination of field monitoring,indoor shear friction test and numerical simulation.The transmission law of jacking force during jacking,the influence law of different contact media on the friction coefficient between pipe joint and surrounding rock,the influence law of buried depth of pipe jacking and parameters of surrounding rock on friction resistance of pipe joint and the maximum number of pipe joints that can be jacked between relays are obtained.Finally,the causes and prevention suggestions of pipe jamming are summarized,and the corresponding treatment measures are put forward in view of the pipe jamming problems in the relying projects.The main research results are as follows:(1)Through on-site monitoring:The dissipation of jacking force along jacking direction is relatively uniform,and the transmission distance of jacking force of different sizes in forward jacking is more than three times that in reverse jacking.(2)The results of indoor shear friction test are obtained:The order of friction coefficient between pipe joint and surrounding rock in different contact media:Pure fresh bentonite mud,waste mud and debris mixing > debris and pure fresh bentonite mud mixing > waste mud and pure fresh bentonite mud mixing > waste mud > pure fresh bentonite mud mixing.When the contact surface is a mixture of fine sand,coarse debris and high viscosity mud,the friction resistance is the highest.It is very easy to cause jamming at this time.(3)The results of numerical simulation are obtained:Buried depth is an important factor affecting the friction resistance of pipe joints.When the burial depth is 50m~100m,the maximum number of pipes that can be jacked in the relay is mainly affected by the burial depth,and the deeper the burial depth,the less the number of pipes that can be jacked in.When the depth of pipe jacking is more than 100 m,the maximum number of pipes that can be jacked in the relay is controlled by both the depth of pipe jacking and the parameters of surrounding rock.At the same burial depth,the larger the friction angle and elastic modulus of rock mass,the more the maximum number of pipes that can be jacked up between relays.(4)The main reasons for pipe jam in the project are: slurry pouring into the outer space of the pipe wall on the excavation surface,rock debris being continuously rubbed and stirred during jacking,and water content of lubricating slurry is reduced.Surrounding rock convergent extrusion pipe joints segregate under the increasing confining pressure,which makes the impurities such as lubricating materials and rock debris gradually become a hard shell wrapped tightly around the pipe joints,eventually resulting in pipe jamming.