Grouting the tail void

Abstract

To fight increasing traffic in city centres, tunnelling can be used to move traffic under the surface of the busy city. However, to prevent damage to the surrounding buildings, the settlements induced by the tunnelling should be kept to a minimum. This thesis researches the influence of the TBM tail void and its grouting process on the settlements. To do so, the monitoring and TBM data from the North/South line in Amsterdam is used. The data of the settlements, grout pressures and grout volumes is searched for locations with sudden changes. For these locations, the development of the settlements as a function of the TBM movement is compared to find out if the changes in settlements are caused by the tail void. This turns out to be the case for half of the researched locations. Furthermore, the changes of the grout pressuresmeasured in the tail void, and the volume injected grout volume are compared for these locations. An increase in injected grout volume shows to decrease the settlements induced by the tail void, while the pressure does not show a correlation with the settlements. Because only one sensor was used for the pressuremeasurements, the grout pressures are then compared for all sensors in the tail void. Again, no correlation is found between the grout pressures and the settlements. A side step in the research shows the development of the grout pressures in the tail void. During the boring process the grout pressures fluctuate. During the boring and forward movement of the TBM the tail void is injected with grout and the grout pressures in the tail void increase. During the ring building phase, this grouting stops and the grout pressures start to dissipate. The amount of dissipation is influenced by the permeability of the surrounding soil. With the help of DIANA FEM software, the influence of the tail void on the total settlements is investigated. The calculations show that a different grouting behaviour caused a change of only 4mmin total settlements. Concluding, as long as the pressures in the tail void stay above the soil pressure the tail void can be filled with grout. The injected grout volume will fill the tail void, preventing the soil from moving into the tail void and with that minimising the settlements at the surface.