Mechanical Properties Of Fiber-reinforced Concrete Pipe And Its Application In Crack Control Of Long-distance Rock Pipe Jacking

The technology of pipe jacking is more and more applied in engineering construction because of its fast,economic,safe and environmental protection.It is developing towards long-distance,large section,deep burial and adapting to complex stratum.In the construction of pipe jacking tunnel in the long-distance rock mass,cracking of concrete pipe frequently occurs,which affects the long-term operation and maintenance of the pipe jacking project.The key to solve this problem is to prevent the pipe from cracking,and to take reasonable construction control measures.Based on Chongqing Guanjingkou Water Control Project,the mechanical properties of fiber-reinforced concrete pipe,the pipe-surrounding rock contact mechanical model,and the causes and control measures of pipe cracks under jacking are studied using theoretical analysis,numerical simulation,laboratory test and field test.The main research contents are as follows:(1)To study the mechanical properties of basalt-polypropylene fiber-reinforced concrete with different fiber mass ratio and concrete control specimens under axial tension,axial compression and four-point bending test.Then,the tensile stress and strain curve and compressive stress-strain curve of the basalt-macro polypropylene fiber-reinforced concrete(HBPFRC)are fitted,and the mechanical action mechanism of the fiber in the concrete under the condition of compression,tensile and bending tests are discussed.The results show that at the total content of 6 kg/m~3,HBPFRC achieves the optimal fiber mixing effect when the mass ratio of basalt fiber to polypropylene fiber is1:2.(2)Three-edge bearing test was used to conduct model tests on no,mano basalt fiber,mano polypropylene fiber,and hybrid-reinforced concrete pipe.The influences of fiber on the bearing capacity,crack load,crack propagation and failure mode of the pipe are studied.On this basis,Abaqus was used to establish the mechanical model of pipe under three-edge bearing test,and the load-displacement curve,failure mode and fracture propagation rule of numerical simulation and model test results of pipe were compared.On this basis,according to the crack load and the limit load of different grades of pipe stipulated in the code,the structural design method suitable for the fiber-reinforced concrete pipe is established,and the reinforcement design of pipe under different diameters and wall thickness is given.(3)In the process of jacking,the contact pressure between the fiber-reinforced concrete pipe and rock was investigated.Under the influence of the jacking force,the changing rules of the axial stress of concrete were investigated.Combined with the feature of rock friction resistance in pipe jacking engineering and the pipe-rock contact condition,the pipe-rock contact mechanical model,which comprehensively considered the contact angle of sediment at the bottom of the pipe,mud buoyancy,axis deviation and pipe-rock friction coefficient,is put forward.The model includes the pipe-slurry contact model,top point contact model,bottom fill contact model and top fill contact model.In addition,the applicable conditions of the models are put forward.The results show that the increase of the angle of sediment at the bottom of the pipe will lead to the increase of pipe-rock contact pressure,and the increase of sediment will lead to the increase of pipe-rock friction coefficient.Thus timely removal of sediment at the bottom of the pipe is an effective way to reduce pipe-rock friction resistance effectively.(4)The numerical model of long-distance rock pipe during the jacking construction period,which considered the pipe-rock contact state,is established.Then,the numerical simulation of fracture distribution and site pipe crack distribution of long-distance pipe jacking engineering rock are compared.It was found that pipe cracking was dominated by large deflection angle and high jacking force,pipe deflection angle and the jacking force value are the two important factors that affect pipe cracking.Increase the wall thickness and the hoop reinforcement ratio can effectively improve the crack load and ultimate load of fiber-reinforced concrete pipe,but the increase of wall thickness sharply increased the weight of pipe and material consumption.The increase of reinforcement ratio on the increase amplitude of cracking load is limited,in contrast,the add of fiber into the concrete cause the weight of fiber-reinforced concrete pipe change little,but can largely raise the crack load and 0.3 mm crack load.Thus,the choice of the fiber-reinforced concrete pipe is an effective method to restrain pipe cracking.(5)The crack propagation law of fiber-reinforced concrete pipe and ordinary concrete pipe under the action of different cracking influencing factors is compared,and the control method of pipe cracking is put forward from the aspects of deflection angle control,jacking force control,manufacturing process improvement and application of fiber-reinforced concrete pipe.The chi-square test in mathematical statistics confirmed the conclusion that the addition of fiber can effectively prevent the pipe from cracking.Besides,the allowable jacking force for preventing pipe cracking on-site under the condition of using traditional concrete pipe and the fiber-reinforced concrete pipe is given,and the design process of the allowable jacking force for preventing pipe cracking in long-distance pipe jacking engineering with universality is further proposed.