Deflection behavior of the steel pipe-jacking in soft soil seabed

摘要

The pipe-jacking method is a kind of efficient trenchless technology to install pipelines, especiallyrnfor the pipeline going through the downtown of the city or the rivers. As the important part of the waterrnsupply project in Xiamen, two steel pipes with 2.2m diameter would be installed to cross the strait betweenrnXiamen Island and the mainland. Considering the navigation channel in the strait, complicated stratums in site,rnand construction techniques and costs, the pipe-jacking method is adopted. Since the longitudinal stiffness of thernsteel jacking pipes is relatively lower than that of the reinforced concrete jacking pipes, the upheaval deflectionrnis more likely to occur on the steel pipes with small buried depth. In this study, the upheaval deflection of thernsteel jacking pipes in the soft soil seabed is analyzed and controlled. The total jacking distance from #2 workingrnwell to #5 working well in this project is 816 m. During the jacking stage, obvious upheaval deflection occursrnin the part under channel area, in where the buried depth of pipes is only 2.96m (i.e. 1.3D). Such upheavalrnmovement also affects the adjacent pipe sections, which causes that the total upheaval length of pipe is aboutrn260 m. Considering the geological condition and influence of the wave, the qualitative and semi-quantitativernanalysis is carried out to investigate the major factors causing the upheaval deflection. Result shows that thernresistance of soil is too small to offset resultant upward forces. Furthermore, the jacking force will contributernto the increase of upheaval after the upward deflection occurs. Therefore, surcharging method is proposed tornreduce the upward deflection of the steel jacking pipes. The field measurement shows that the deflection of steelrnpipes decreased after loading in pipes. This study will provide the beneficial reference for the design and thernconstruction of the steel jacking pipes in soft soil seabed.