The Calculation of The Thrust Force for Pipeline Installation Using The Direct Pipe Method
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The Direct Pipe method enables to lay a prefabricated pipeline in one single, continuous working operation into the ground with the aid of the thrust unit “Pipe Thruster”. As with Pipe Jacking, earth excavation is executed by means of a navigable microtunnelling machine, which is directly coupled with the pipeline The tunnel face is slurry supported and often uses a bentonite suspension for controlled excavation of the soil. Due to the success of the new method several other projects have been carried out. The magnitude of the thrust force generated by the Pipe Thruster is an important topic of the design of a Direct Pipe project. The thrust force is required to push the pipeline into the borehole and was investigated by means of Finite element calculations using the ABAQUS software package. The analysis of the Finite element calculation results shows several mechanisms, which contribute to the thrust force. The mechanisms have a strong interaction with each other. Formulas for the calculation of the Thrust Force were deduced per mechanism and per section of the drilling line. The measurement results of the thrust force from several projects, which have been carried out recently, were compared with the calculated thrust forces using the new set of formulas. The results are quite promising. The effect of a higher friction after a standstill period is currently still a research topic. Soon a decision will be made whether the time dependent standstill effect can be calculated based on physical processes in the bore hole, or whether a practical approach should be applied to estimate the time dependent standstill effects.
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