Experimental Study On Deformation Characteristics Of Buried Polyethylene Pressure Pipe Under Complicated Load

In municipal buried pipeline applications,PE pipe is widely used at home and abroad because of its advantages of light weight,corrosion resistance,smooth pipe wall,large overcurrent capacity and large deformation capacity to adapt to site settlement.It is a trend to replace traditional pipe in some areas of application,such as urban drainage.With the increasing use of PE pipe,the use of the gradual expansion of the PE pipe in the use of the mechanical environment to deal with more and more complex.However,the current research on PE pipe mainly focuses on the relevant failure modes and life prediction under the effect of hydrostatic pressure.The research under complex load has just started,and the research mainly focuses on the polyethylene material itself,without considering the situation of buried pipe and soil interaction.The domestic and international research on the buried pipeline reaction under typical complex loads is mostly steel pipe,which is not suitable for the PE pipe.The study also did not consider the influence of pipeline pressure on the pipe deformation.In order to improve the safety of buried PE pipe,it is urgent to carry out the research on the strength of buried PE pipe under complicated load condition and provide the technical support for the corresponding safety assessment method.In this paper,the effects of burial conditions,pipe-soil interaction and working pressure on the deformation of buried polyethylene pipes are also considered.A test model of the buried polyethylene pipe reaction under various load conditions and the experimental model of the buried polyethylene pipe reaction under the site subsidence were established.By injecting compressed air into the pipe and changing the thickness of the cover soil above the top of the pipe,the deformation characteristics of the buried polyethylene pressure pipe under the condition of casing load were studied.The influence of different influencing factors(working pressure,cover soil thickness and tube soil strength)on the deformation of buried polyethylene pipes was analyzed.In the center of the bottom of the model,a settling plate with a length of 1.2m and a width of 1.0m that can be moved downwards is set.By changing the vertical displacement of the settlementplate,the effect of site subsidence on the deformation of the buried polyethylene pipe is simulated.The effect of buried polyethylene pipe on the contents of vertical displacement,strain distribution,location of dangerous point and the sensitive factors of dangerous point strain under different working pressure and soil settlement was studied.The experiments shows:(1)Under the combined action of casing load and working pressure,the maximum strain point of buried polyethylene pipe is located at the top of the pipe,the strain on the left and right sides of the pipe is second,and the strain at the pipe bottom is the smallest,all of them are circumferential strain.(2)The working mechanism of flexible pipe and rigid pipe is different.The tube soil is not only the acting load,but also a medium to enhance the strength and rigidity of the pipe.The strength of the filled soil within a certain pipe circumference is a sensitive factor that affects the deformation of the buried polyethylene pipe.(3)Under the combined action of casing load and working pressure,the maximum strain of buried polyethylene pipe did not change obviously with the thickness of cover soil when the thickness of cover soil changed from 50 cm to100cm.(4)Under the joint action of casing load and working pressure,the maximum strain value of buried PE pipe increased with the increase of working pressure,and there was a clear linear relationship between working pressure and maximum strain value.(5)Under the action of site subsidence,when the subsidence volume changes within the range of 0-200 mm,the dangerous point of the polyethylene pressureless pipe is located at the bottom of the central section of the pipe in the subsidence area,and the strain is longitudinal tensile strain.Under the action of site subsidence,when the subsidence volume changes within the range of250-500 mm,the dangerous point of the polyethylene pressureless pipe is located at the top of the central section of the pipe in the subsidence area,and the strain is longitudinal compressive strain.(6)The dangerous point of polyethylene pressure pipe is located at the top of the central section of the pipe in the subsidence area under the action of site subsidence,and the strain is ring pull strain.Moreover,the strain at the dangerous point of buried polyethylene pipe increases with the increase of working pressure.However,when the subsidence is large,the working pressure is the secondary influential factor on the deformation of the polyethylene pipe.Whether the buried polyethylene pipe is damaged or not is mainly controlled by the longitudinal compressive stress caused by longitudinal bending of the pipe.The dangerous point of the polyethylene pressure pipe is located at the top of the central section of the pipe in the subsidence area when the subsidence is large,and the strain is longitudinal compressive strain.(8)The maximum strain value of buried polyethylene pipe increases with the increase of settlement under the action of site subsidence.(9)The soil arching formed during the site subsidence reduces the load on the overburden of the buried polyethylene pipe and plays a protective role in the safe operation of the buried polyethylene pipe.(10)The maximum vertical displacement of buried polyethylene pipe increases with the increase of settlement under the action of site subsidence,but the displacement value is much smaller than the amount of soil subsidence.This is because the sand in the non-subsidence area loses the lateral restraint effect,while the sand has strong flow characteristics and will move to the subsidence area,which will slow down the downward subsidence of the buried polyethylene pipe.It protects the buried polyethylene pipe under the action of site subsidence.