Study On Mechanical Behaviors Of Buried Pipelines Under Traffic Loads

The traffic load is one of the important live loads carried by buried pipelines under pavement surface. With the rapid development of economy and transportation industry in China, various problems of buried pipelines, such as damage and failure caused by vehicle loads, should be paid more attentions. The most of existing researches on mechanical behavior of buried pipelines was mainly focused on aspects such as soil pressure (static) and seismic responses (dynamic) of pipelines, etc., but the effects of vehicle loads have rarely been investigated. In this thesis, a literature review is first carried out on the state-of-the-art of the simplified models of traffic loads, and the static and dynamic analyses of buried pipelines. Based on the literature review, a systematic method, integrating theoretical analysis, numerical simulation, verification by case studies, and current standards, is then developed for studying the characteristics of dynamic vehicle loads on rough pavement, soil pressure on the pipelines and the pipeline-soil interaction, the static and dynamic responses under vehicle loads, and the measures to reduce loads on the pipelines. Finally, a field test is carried out and used to validate the developed finite element analysis (FEA) models. The main research findings are summarized as follows,A quarter-vehicle vibration model with two degrees of freedom and four vehicle parameters was built and the pavement surface roughness (PSR) was taken as the excitation in this model. The stochastic vibration theory was used to analyze the dynamic vehicle loads on rough pavement. The probability distribution of dynamic vehicle loads, dynamic load coefficient, peak dynamic load coefficient and the effects of velocity, suspension mass and the four parameters of the vehicle and the PSR on dynamic load coefficient were then obtained. The expression of equivalent dynamic load coefficient (EDLC) of vehicle on concrete pavement was deduced, based on the Palmgren-Miner linear cumulative damage theory and the relationship between random and certain vehicle dynamic loads was established.Soil is the medium transferring loads from the vehicle to the buried pipelines. The effects of vehicle loads on buried pipelines are expressed by pipeline-soil interaction. Therefore, the evaluation of soil pressure and pipeline-soil interaction is the basis for the mechanical analysis of buried pipelines. Aiming at the problems of assumption of slip surface adopted by most of pipelines soil pressures models, elastic analytical solution was developed, based on displacement compatibility on pipe wall. In this way, the relationship between stress around pipe-wall and section stiffness was built and the methods for calculating soil pressure on rigid and flexible pipelines were unified.