Numerical Simulation On The Mechanical Properties Of Buried GRP Pipe

Glass fiber reinforced plastic pipe is a new kind of flexible composite pipe with theadvantages of light, high-strength, durable, good hydraulic characteristics, easyinstallation and low comprehensive cost and so on. Due to these outstanding advantages,the GRP pipe is widely applied in heating, water supply, construction, chemical industry,petroleum, energy and other fields. However, for the reasons of the design, the pipeaging and construction quality, the buried GRP pipe may deform excessively in service,damage prematurely and affect the normal operation of the pipeline seriously. On thebackground of the pipe buried under West Outlets in Northern New District, Chongqing,owing to the quality defects of backfill soil and poor construction which engendered theburied GRP pipe’s structure damaged after using one year, this paper has explored thepossible reasons for pipe’s damage and studied the stress and deformation performanceof buried GRP pipe under the action of main influence factors, and put forward amodified calculation formula of soil pressure according to the analysis and calculationresults.This paper has reviewed the existing design theories of pipeline, pointed out theproblems existing in the design theories of flexible pipe and analyzed the mechanicsperformance in cross-section of buried GRP pipe adopting the elastic theory. The majorfactors which generate buried GRP pipes to damage prematurely has been ascertained,involving modulus of backfill soil, pipe stiffness, the construction quality defects ofpipe’s foundation.Since the buried GRP pipe belongs to flexible pipe in general, pipe-soil interactionshould be taken into account in the course of buried flexible pipe design. Therefore,both related contact theory and parameter-friction coefficient on the contact surface areintroduced in this paper. As is known to all, contact force embodies the normal forceand tangential force. However, the tangential force of sliding surfaces is modeled with aCoulomb friction law. The value of friction coefficient affects that of contact forcedirectly, so it is indispensable to investigate the influence of friction coefficient exertingon the pipe stress performance.Finite element method has been applied to analyze the impact of pipe-soil relativerigidity, friction coefficients, rigidity defects of pipe foundation on the pipe stressperformance. The results reveal that with the modulus of backfill soil increasing, vertical earth pressure on the top and horizontal earth pressure at horizontal diameter ofthe pipe would decrease. The deformation of pipe under load is inversely proportional tomodulus of soil. With the increase of friction coefficient on contact surfaces, thedistribution pattern of the total earth pressure becomes double peak from single peakand meanwhile the peak stress of pipe raises. The weak area of pipe foundation stiffnessboth in plane and along the pipe length direction can result in stress concentration on thepipe. The weaker the stiffness is, the more obvious the stress concentration changes.This paper proposes the modified calculation formula of earth pressure, by themeans of the effect of the modulus of backfill soil, friction coefficient, The weakness ofpipe foundation stiffness casting on the stress peak of the pipe, based on analysis andcalculation results.