The cast-iron line of DN400 mm to DN500 mm under the Ziyang Road in the downtown area of Wuhan City was serviced by HDPE pipe steining process.

Taking the typical section of river-crossing pipeline as the study subject,the experimental study and theoretical analysis are made on the relationship between the safety of the crossing section and the related river regime,flood characteristics and the protection coverage;in which the key problems to be solved in the experiment and engineering design concerned are discussed and analyzed.

Based on several typical sections of river bends,the effects from both the evolution of river regime and the bend-flow on river-crossing pipeline,such as the erosions from longitudinal and transverse flows,the uplift and pressure drag caused by the flow around pipe and the momentum and angular momentum caused by the induced velocity between transverse circle flows,etc.

The paper puts forward the FAHP method to determine the pipeline crossing program instead of AHP method,and considers the FAHP method as simpler than the latter.

The pipeline crossing project has the features of long distance,steep slope and complicated circumstances.

s By taking the pipeline crossing as a practice example,the writer expounded the principle &method of earthless cofferdam technique and introduced the determination method of cofferdam location,skeleton structure of cofferdam,lay down of support board &waterproofing measure etc.