THREE DIMENSIONAL FINITE ELEMENT ANALYSIS OF SHALLOW SOIL TUNNELING

One of the most innovative improvements in tunneling technology in the past decade has been the introduction of advanced soil tunneling shield machines. Examples of these new machines are the Slurry and Earth Pressure Balanced shield machines. The most important feature of these machines is that they allow the application of continuous support to the face of the tunnel.;Due to the lack of proper analytical or field data, it is not exactly clear how much greater a degree of ground control is achieved with the advanced shield machines over conventional ones. This dissertation presents a true three dimensional finite element model which can be used to compare different soil tunneling procedures, especially the deformation patterns associated with these procedures. Parametric studies of various factors affecting shield performance are described.;The results demonstrate the benefits of continuous face support. Generally, settlements are reduced if the advance shield machines are operated in such a way that they initially cause a slight movement away from the face of the shield. Subsequently, settlement occurs due to the closure of the tail void as is the case with the conventional shield. For both the advanced and conventional shield machines, soil movement in the tail void has a major influence on the final ground movement. Also, for both shield types, the deformation patterns predicted by the analytical model are consistent with those observed in the field.;Future studies are necessary to optimize the amount of beneficial initial heave at the face of the advanced shield machines. Such studies should also include the application of some of the concepts of the advanced shield machine to tail void support.