Efficiency of embedded barriers to mitigate tunnelling effects

Ground displacements caused by underground excavations in densely urbanised areas often requires the adoption of protective techniques to prevent damage to existing buildings. When the tunnel passes to the side of a potentially affected building, tunnelling-induced settlements can be reduced pre-installing a protective barrier between the tunnel and the building. Usually, this mitigation technique is implemented in practice based on empirical knowledge rather than as a result of a rational design process. This paper presents a numerical study to evaluate the efficiency of different schemes of embedded barriers, using numerical analyses as a tool to understand the main mechanisms of soil-barrier interaction. Two- and three-dimensional FE analyses were carried out assuming a continuous embedded diaphragm wall or a discontinuous piled wall. The barrier was assumed of either infinite or finite horizontal extension, to evaluate the minimum extension needed to obtain in a given section a settlement reduction similar to that attained under plane strain conditions. The effects induced by wall installation and those associated to the presence of a pre-existing building were also accounted for. The results of the analyses permitted to recognise the main factors affecting the efficiency of a protective barrier, providing some guidance for a rational design of the intervention.