Scale Laboratory Model for Studying the Behavior of Pipe Umbrella in Sandy Soil

Steel pipe umbrellas have been used to tunnel in difficult conditions or in weak rock masses and/or soils. Despite the large number of applications around the world, there are still some doubts concerning how pipe umbrellas behave under loading when the tunnel face advances. For this reason, a scale laboratory model of pipe umbrella reinforced tunnel heading in a sandy soil was set up with the aim of understanding tunnel boundary deformation mechanisms in order to understand and define which is the best pipe umbrella design. The laboratory tests were performed using a box (1.5 m x 2.0mx 1.8 m) in which the excavation of a 50 cmdiameter tunnel at a low depth was simulated. The behavior of the ground and of some pipes of the umbrella was monitored during the test and the results were compared with FLAC 3D program modeling results. The paper reports the preliminary results of the first set of tests which, however, demonstrated the great efficiency of the pipe umbrella system, even for heading of half of the tunnel diameter, that the behavior of the tunnel face is a key parameter in the deformation scheme and that this support technique can be modeled using a three dimensional code.