The pipelines buried in soil may become spanned under the scouring action of wave and current. Based on the project in which the pipelines laid among the artificial island No.1, No.3 and the platform No.1, Nan Pu oil field, the study of the displacements and the inner force of spanned pipelines is performed, in which the interaction between pipe and soil is taken into consideration. The buried pipeline is regarded as Winkler beam. The load on spanned pipeline includes two types: the uniform load and the concentrated load, induced by pipe gravity, transported medium gravity, wave, current and so on. Hence, in this paper the responses of the spanned and the buried pipeline, including the displacement and inner force, are studied and the analytic solution of them is obtained. At last, the method is validated and used to calculate the displacements and the inner force of spanned pipeline in Nan Pu oil field under a working condition.
With the exploration of oil field in the sea, a large member of pipelines is laid all over the world. The pipelines buried in soil may become spanned when they are scoured by wave and current (Sumer, Whitehouse and Torum, 2001). It is of important interest to study the displacement and the inner force of spanned pipelines for it can be used to guide the safety maintenance of pipelines. If the boundary of spanned pipeline is considered to be fixed or hinged, the calculation is easy to deal with. However the results based on them are of little accuracy. If the complicated mechanics property of soil is considered (Ose, Yong, Nystrom and Damsleth, 1999), it is difficult to calculate the responses of spanned pipeline. According to the Winkler model (Hetenyi, 1946; ShuHeng, 2005; Wang, 2008), the beam-supporting soil is modeled as a series of closely spaced, mutually independent, linear elastic vertical springs, which provide resistance in direct proportion to the deflection of the beam.
