Research On Jacking Force And Stability Of Large Diameter Pipe Jacking In Sand Formation

In the long-diameter pipe jacking projects, resistances must be overcome by jacking force from the jacking machine in order to move the pipes successfully. And The thixotropic slurry is usually injected between the soil and structure to reduce the friction on the outside surface of the structure. Therefore, knowing the jacking force during the jacking procedure and pre-evaluating stability of the jacking pipes in sand formation are deemed very important.For the background of pipe jacking engineering in sand and gravel formations in Shenyang which is encountered large diameter in this study. The experience of pipe jacking in sand and gravel formations in Shenyang is very limited, especially for pipes with large diameter. A numerical method of estimation on the jacking force during construction was given based on the initial jacking force monitored in situ. The jacking forces during jacking procedure were calculated by numerical method and compared with in-situ monitored values. Meanwhile, the effect of resistance relieving by using different proportion of thixotropic fluids was numerically analyzed and the jacking forces when using seven kinds of fluids were compared. Finally, the construction stability in grouting and rectification was numerically analyzed and the safety factor of excavation face was obtained by strength reduction method.Results indicate that the numerical method used in this work is feasible in forecasting the jacking force, thus being helpful in reasonably arranging the intermediate jacking stations. The water content in thixotopic fluids has significant influence on the resistance relieving effect of pipe jacking. An optimized propotion of bentonite and water was proposed as 1:9. It is also shown that the maximum pressure stress of pipes has been enlarged by the rectification load, which should be under 1MPa. In order to ensure the stability of the ground surface during pipe jacking, it is suggested that the supporting pressure of the excavation surface should be exerted against more than 20 kPa to the excavation surface, under which the safety coefficient of the excavation surface is 1.39.