Numerical modelling of soil-pipeline interaction

• Main Author: Cheong, T. P.
• Published: University of Cambridge 2007
• Subjects: 624.15
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597580

This thesis investigates the interaction between soil and pipeline in sand subjected to lateral ground loading. The purpose of this study is to improve the structural modelling of buried pipelines; and also aims to produce design guidelines and construct normalised charts which will be of direct benefit to practising pipeline engineers. The research was performed entirely using the finite element (FE) method, and utilised the user subroutine of an advanced constitutive soil model that was implemented in this thesis. The problems examined in this research can be categorised into four main topics. First, 2-D FE analyses were conducted concerning with the effects of loading rate on a laterally-loaded pipeline buried in saturated sand. All indications support the conclusion that both the sand dilatancy and hydraulic conductivity of the soil in relation to the loading rate are important factors for mobilisation of the lateral resistance of a pipeline in a saturated soil medium. Second, soil loading on a pipeline under global soil shearing conditions was investigated by performing different types of relative ground and pipeline movement modes, with the aim of generating both <i>passive </i>and <i>active </i>failure states. Overall, it can be concluded that the effect of global soil shearing on the interaction of soil and pipeline is relatively small in terms of <i>N_q</i>_,implying that local soil deformation and soil dilation characteristics are most important and influential factors contributing to the magnitude of the lateral pressure on pipelines. Third, investigations of the behaviour of an elbow-bend pipe, under lateral soil loading were performed using a 3-D FE modelling method. It was found that deeper burial pipeline, denser soil and elbow-bend pipe with larger bending angle accounted higher <i>N_q</i>. Also <i>N_q</i> at the elbow-bend pipe was about 2.7 times higher than a straight pipe. The results confirmed that the ‘3-D elbow effect’ can be ignored in the closing mode case, but in the opening mode case, the effect was computed at about 17% when compared to a 2-D bilinear soil-spring model case. Additionally, a larger effective plastic strain region was observed when 3-D soil-spring models were adopted in the design. Fourth, in order to achieve a reliable design procedure against permanent ground deformation (PGD), a full-scale 3-D FE numerical analysis and a full-scale 3-D spring model analysis were both carried out on a 90° elbow pipeline. Encouraging and good results were achieved from both of the numerical models when compared with the data from experiments carried out at Cornell University. Thus, it is shown that the adopted 3-D FE method was able to simulate the observed pipeline performance under PGD ground failure in a reliable way.