A system for direct and continuous measurement of the void around the shield of a TBM during excavation

摘要

The normal excavation of the ground using a shield TBM creates an annular space, the "tail void" or gap, around the extrados of the shield. The gap thus produced is of variable dimension around the body of the Shield. In weak ground, this gap will induce convergence or collapse to fill it to provide support. Knowing the "real" dimensions of the void around the shield of a TBM during its advancement would provide important information about the stability conditions of the ground being excavated, the conditions of wear of the peripheral cutting tools, and the presence or not of any excessive deformation phenomenon above the shield which could migrate to the ground surface. The conclusion from our literature search and field experience is that "today there still does not exist a satisfactory method (direct or indirect) for measuring the void between the shield and the excavated profile". The solution is to realize a device for measuring void (DMV), that does not require any significant modification of the shield itself and permits to measure the void, directly and precisely, during construction of a tunnel using shielded TBM, solving with just one system the problem described previously. The device can eventually be proposed as a prototype to the TBM manufacturers in order to be adapted and implemented as an integral and indispensable part of a shielded TBM. Besides, the proposed device does not interfere with the routine excavation activities inside the shield and thus will not at all penalize the production. A fundamental objective of the in-house research effort initiated by Geodata to seek for, through the stages of feasibility study and design of the prototype DMV, a direct method for measuring-monitoring systematically and with high reliability the void space at the extrados of the shield during tunnel excavation. Such an innovative solution shall then be adopted by constructors of shielded TBMs. The scope of the research and development study shall be fulfilled when every aspect of the innovation is defined, and the prototype is designed, developed, and experimented (also in field scale) to demonstrate its benefits, solving all problems or removing weaknesses related to the indirect methods based on geophysical principles.