ACOUSTIC INSULATION PROVIDED BY A SINGLE WALL SEPARATING TWO CONTIGUOUS TUNNELS VIA BEM

This paper describes the computation of the acoustic insulation provided by a single simple wall separating two contiguous tunnels when a steady state, spatially sinusoidal, harmonic line load pressure excites one of the tunnels. The Boundary Element Method (BEM), formulated in the frequency domain, is used to compute the acoustic pressure in the two tunnels. The insulation conferred by the wall is characterized, identifying the location of insulation dips in the frequency domain with those dips related to its own natural dynamic vibration modes and those related to the natural vibration modes of the tunnels. This model is also used to assess how the dimension of the rooms, and the rigidity and thickness of the wall affect acoustic insulation. The transmission loss results obtained via the BEM are then compared with those provided by simplified analytical models such as the mass law.